**Hearing Loss and the Voice**

#### **Chapter 6**

### **Hearing Loss and the Voice**

Ana Cristina Coelho, Daniela Malta Medved and Alcione Ghedini Brasolotto

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/61217

#### **Abstract**

The voice varies according to the context of speech and to the physical and psycholog‐ ical conditions of the human being, and there is always a normal standard for the vo‐ cal output. Hearing loss can impair voce production, causing social, educational, and speech limitations, with specific deviation of the communication related to speech and voice. Usually, the voice is not the main focus of the speech-language pathology ther‐ apy with individuals with hearing loss, but its deviations can represent such a nega‐ tive impact on this population that it can interfere on speech intelligibility and crucially compromise the social integration of the individual. The literature vastly ex‐ plores acoustic and perceptual characteristics of children and adults with hearing loss. Voice problems in individuals with this impairment are directly related to its type and severity, age, gender, and type of hearing device used. While individuals with mild and moderate hearing loss can only present problems with resonance, severely im‐ paired individuals may lack intensity and frequency control, among other alterations. The commonly found vocal deviations include strain, breathiness, roughness, mono‐ tone, absence of rhythm, unpleasant quality, hoarseness, vocal fatigue, high pitch, re‐ duced volume, loudness with excessive variation, unbalanced resonance, altered breathing pattern, brusque vocal attack, and imprecise articulation. These characteris‐ tics are justified by the incapability of the deaf to control their vocal performance due to the lack of auditory monitoring of their own voice, caused by the hearing loss. Hence, the development of an intelligible speech with a good quality of voice on the hearing impaired is a challenge, despite the sophisticated technological advances of hearing aids, cochlear implants and other implantable devices. The purpose of this chapter is therefore to present an extensive review of the literature and describe our experience regarding the evaluation, diagnosis, and treatment of voice disorders in in‐ dividuals with hearing loss.

**Keywords:** Hearing loss, voice, voice quality

© 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **1. Introduction**

Didactically, the voice is described as the resulting sound of the vibration of the vocal folds, which is amplified by the vocal tract resonators. The vocal tract articulators modify this sound producing recognizable vowels and consonants. A pleasant and socially acceptable voice production is highly dependent on emotional, social, and physical conditions, the latter including auditory monitoring of the voice.

Hearing loss can impair oral communication, causing social, educational, and speech limitations, with specific deviation of the communication related to speech and voice. Usually, the rehabilitation process prioritizes auditory abilities, and therefore, the voice is not the main focus of the speech-language therapy with individuals with hearing loss. Its deviations, however, can represent such a negative impact on this population that it can interfere on speech intelligibility, cause a negative impact on the listener, and crucially compromise the social integration of the individual.

The challenges of voice production in individuals with hearing loss involve alterations in respiration, phonation, and articulation [1]. Also, voice problems in individuals with this impairment are directly related to its type and severity, age, gender, and type of hearing device used [2]. While individuals with mild and moderate hearing loss can only present problems with resonance, severely impaired individuals may lack intensity and frequen‐ cy control, among other alterations [3]. Hence, the development of an intelligible speech with a good quality of voice in individuals with hearing loss is a challenge, despite the sophisticated technological advances of hearing aids, cochlear implants and other implant‐ able devices.

#### **2. The auditory system and voice production**

Voice production (Figures 1A–1H) occurs by the integration of the respiratory, phonatory and articulatory systems, and also involves highly complex mechanisms of structures related to the central and peripheral nervous systems (Figure 1A) [4]. The airflow that is moved out of the lungs during expiration by the coordinated action of the diaphragm, abdomi‐ nal muscles, chest muscles, and rib cage is directed toward the vocal folds (Figure 1B). Then to produce sound, the vocal folds are moved to midline by the action intrinsic muscles, nerves, and cartilages (Figures 1B–1D). The column of air from the lungs creates subglot‐ tic pleasure, causing the opening of the vocal folds. This is the beginning of a vibratory cycle that occurs repeatedly. In one vibratory cycle, the column of air pressure opens the bottom of the vocal folds. Then the air continues to move upward, now toward the top of the vocal folds, opening them entirely. The low pressure created behind the fast-moving air column produces the "Bernoulli effect", which causes the bottom to close, followed by the top. The closure of the vocal folds cuts off the air column and releases a pulse of air, and the cycle recommences (Figure 1E). The rapid pulses of air created in the repeated vibratory cycles produce "voiced sounds", which is then amplified and modified by the vocal tract resonators. The nose, pharynx, and mouth amplify and modify sound, allow‐ ing it to take on the distinctive qualities of voice. Finally, the articulators produce recogniz‐ able words [5] (Figures 1F–1G).

**1. Introduction**

104 Update On Hearing Loss

able devices.

latter including auditory monitoring of the voice.

compromise the social integration of the individual.

**2. The auditory system and voice production**

Didactically, the voice is described as the resulting sound of the vibration of the vocal folds, which is amplified by the vocal tract resonators. The vocal tract articulators modify this sound producing recognizable vowels and consonants. A pleasant and socially acceptable voice production is highly dependent on emotional, social, and physical conditions, the

Hearing loss can impair oral communication, causing social, educational, and speech limitations, with specific deviation of the communication related to speech and voice. Usually, the rehabilitation process prioritizes auditory abilities, and therefore, the voice is not the main focus of the speech-language therapy with individuals with hearing loss. Its deviations, however, can represent such a negative impact on this population that it can interfere on speech intelligibility, cause a negative impact on the listener, and crucially

The challenges of voice production in individuals with hearing loss involve alterations in respiration, phonation, and articulation [1]. Also, voice problems in individuals with this impairment are directly related to its type and severity, age, gender, and type of hearing device used [2]. While individuals with mild and moderate hearing loss can only present problems with resonance, severely impaired individuals may lack intensity and frequen‐ cy control, among other alterations [3]. Hence, the development of an intelligible speech with a good quality of voice in individuals with hearing loss is a challenge, despite the sophisticated technological advances of hearing aids, cochlear implants and other implant‐

Voice production (Figures 1A–1H) occurs by the integration of the respiratory, phonatory and articulatory systems, and also involves highly complex mechanisms of structures related to the central and peripheral nervous systems (Figure 1A) [4]. The airflow that is moved out of the lungs during expiration by the coordinated action of the diaphragm, abdomi‐ nal muscles, chest muscles, and rib cage is directed toward the vocal folds (Figure 1B). Then to produce sound, the vocal folds are moved to midline by the action intrinsic muscles, nerves, and cartilages (Figures 1B–1D). The column of air from the lungs creates subglot‐ tic pleasure, causing the opening of the vocal folds. This is the beginning of a vibratory cycle that occurs repeatedly. In one vibratory cycle, the column of air pressure opens the bottom of the vocal folds. Then the air continues to move upward, now toward the top of the vocal folds, opening them entirely. The low pressure created behind the fast-moving air column produces the "Bernoulli effect", which causes the bottom to close, followed by the top. The closure of the vocal folds cuts off the air column and releases a pulse of air, and the cycle recommences (Figure 1E). The rapid pulses of air created in the repeated The neural component of the voice production generates two components for the voice: a propositional and an emotional one. The propositional vocalization is the expression of any idea that can be an abstract thought, an action, or an appreciation. Its content is not important if it has a communication proposal by means of the voice. The emotional vocalization expresses the emotional components of phonation. Both systems converge or integrate in the brainstem region where the retroambiguus nuclei are located. There, a new recording and a new result occur. This information goes to the nucleus ambiguus and retrofacial nucleus, which originate the vagal fibers of superior and inferior (recurrent) laryngeal nerves [6]. The peripheral nerves directly related the voice, providing sensory and motor innervation of the vocal tract include the glossopharyngeal nerve (IX cranial nerve), the trigeminal nerve (V cranial nerve), the facial nerve (VII cranial nerve), the vagus nerve (X cranial nerve), and the hypoglossal nerve (XII cranial nerve) [6].

Voice and speech production is therefore a complex process and involves numerous regulatory mechanisms [7]. In addition, during the whole process of maturation of the voice, people develop phonatory control and abilities to regulate and vary the voice use in different situations, which is directly related to a key component, which is the auditory feedback of the voice [8].

The auditory system is essential to regulate voice production by monitoring different voice parameters [9]. It provides two types of control over speech production: feedback control and feedforward control [10]. The feedback control monitors task performance during execution and also deviations from the desired performance, which are corrected according to sensory information. In the feedforward control, task performance is executed from previously learned commands, without reliance on incoming task-related sensory information. Speech and voice production involve both feedforward and feedback control, and auditory feedback impacts both control processes [11] (Figure 2).

Also, the auditory system has three roles: providing information regarding voice targets, which is important for corrections in pitch, volume, and other attributes that may affect intelligibility of speech; providing feedback about environmental conditions, which is important in noisy situations, for example, so that the speaker knows to enunciate more clearly, to increase amplitude, and to reduce speaking rate to increase intelligibility; and contributing to the generation of internal models for the motor plans for voice production, which is essential to the maintenance of a rapid speech rate through development of internal models, allowing for the vocal tract and related structures to be prepared before vocalization and for speech to continue without constant auditory feedback [10, 12]. These roles are responsible, therefore, for modeling voice quality, pitch, loudness, resonance, articulation, and speech rate.

Figure 1. Voice production. (A) Peripheral innervation of the vocal tract; (B) respiration; (C) larynx; (D) intrinsic muscles of the larynx; (E) vibratory cycle; (F) vocal fold adduction; (G) extrinsic muscles of the larynx; (H) resonators and articulators. Source: Virtual Man Project [4]. **Figure 1.** Voice production. (A) Peripheral innervation of the vocal tract; (B) respiration; (C) larynx; (D) intrinsic mus‐ cles of the larynx; (E) vibratory cycle; (F) vocal fold adduction; (G) extrinsic muscles of the larynx; (H) resonators and articulators. Source: Virtual Man Project [4].

**Figure 2.** Auditory monitoring of voice production.

A B

C D

E F

G H

**Figure 1.** Voice production. (A) Peripheral innervation of the vocal tract; (B) respiration; (C) larynx; (D) intrinsic mus‐ cles of the larynx; (E) vibratory cycle; (F) vocal fold adduction; (G) extrinsic muscles of the larynx; (H) resonators and

larynx; (H) resonators and articulators. Source: Virtual Man Project [4].

articulators. Source: Virtual Man Project [4].

106 Update On Hearing Loss

Figure 1. Voice production. (A) Peripheral innervation of the vocal tract; (B) respiration; (C) larynx; (D) intrinsic muscles of the larynx; (E) vibratory cycle; (F) vocal fold adduction; (G) extrinsic muscles of the

#### **3. The voice of individuals with hearing loss**

The overall product of a deaf speaker's vocal apparatus depends on the respiratory conditions, laryngeal state, resonators, articulators and prosodic aspects such as intensity, intonation, rhythm, and frequency.

Respiration aspects related to phonation can also be altered in this population. Laryngeal aerodynamics between children with bilateral profound sensorineural hearing loss using hearing aids and normal hearing children were compared by measuring vital capacity, peak flow, maximum sustained phonation, and fast abduction-adduction rate [13]. The authors found significant differences between vital capacity, maximum sustained phonation, and abduction-adduction rate, but not air flow, suggesting the presence of physiologically healthy and functional lungs for the airflow supply that will be required for speech production, but a limited use of the lung volume, poor management of the air supply, and poor laryngeal control during phonation.

Another potential factor that affects voice and speech intelligibility in individuals with hearing loss is the articulation accuracy of consonants and vowels. It is important to consider that voice and articulation are closely related since the sound that comes from the larynx is transformed into words by its combination with the dynamic and static structures of the upper vocal tract.

The phonetic inventory of the consonants in individuals with hearing loss can be compromised by distortions, substitutions, and omissions. Some phonological processes such as deletion of final consonants, cluster reduction, stopping, and devoicing may also occur [14], especially with voiced sounds and high frequency fricative consonants. The articulation of individuals with hearing loss has been reported to be characterized by the absence of some fricatives, the presence of distortions, and phonological disorders [15]. An adequate vowel production depends on the shape of the lips and position of the tongue and is also affected by the lack of auditory monitoring of the voice [16].

Regarding all aspects of voice production, the voice of individuals with hearing loss has been widely described. Specifically, acoustic and perceptual findings (Tables 1 and 2) indicate alterations that go from minor loudness deviation to significant respiratory, phonatory, and articulatory disorders. However, these characteristics are inconsistent and not unanimous among authors. They are reported to depend on age of hearing loss onset, its type and severity, and on the treatment of choice (Table 1) and have been compared among groups of patients in different conditions: prelingually deafened and postlingually deafened, aided and unaided, pre and post cochlear implantation, and patients treated with either hearing aids or cochlear implants (Table 2).

Such a variety of vocal features and results (Tables 1 and 2) are possibly due different meth‐ odological approaches with different assessment conditions, such as different speech materi‐ als, different assessment techniques, different software, different perceptual protocols, number of participants, different age range, different hearing devices, different age at the activation of the hearing device, and presence or absence of a control group to establish normative data [17]. Therefore, the understanding of speech and voice production of individuals with hearing loss is still a challenge and is missing a standardized approach.



presence of distortions, and phonological disorders [15]. An adequate vowel production depends on the shape of the lips and position of the tongue and is also affected by the lack of

Regarding all aspects of voice production, the voice of individuals with hearing loss has been widely described. Specifically, acoustic and perceptual findings (Tables 1 and 2) indicate alterations that go from minor loudness deviation to significant respiratory, phonatory, and articulatory disorders. However, these characteristics are inconsistent and not unanimous among authors. They are reported to depend on age of hearing loss onset, its type and severity, and on the treatment of choice (Table 1) and have been compared among groups of patients in different conditions: prelingually deafened and postlingually deafened, aided and unaided, pre and post cochlear implantation, and patients treated with either hearing aids or cochlear

Such a variety of vocal features and results (Tables 1 and 2) are possibly due different meth‐ odological approaches with different assessment conditions, such as different speech materi‐ als, different assessment techniques, different software, different perceptual protocols, number of participants, different age range, different hearing devices, different age at the activation of the hearing device, and presence or absence of a control group to establish normative data [17]. Therefore, the understanding of speech and voice production of individuals with hearing loss

Sensorineural High fundamental frequency (f0) [18–21], f0 within normal standards

amplitude, and f0 [22] instability [23,24]

irregularity [17,21,30], instability [24,26] Postlingual Abnormal intonation [21,28], high pitch/f0 [21,31], altered speech rate

[15], normal jitter [15], normal shimmer [15], high variation of

variability in f0 [21,26], excessive intonation [21], monotone [20], excessive pitch variation [21], altered speech rate [21], increased loudness [21,29], loudness either to soft or too loud [20], resonance

[21,28], nasality [2,21], loudness deviation [2,21,28,31], roughness [1], strain [1], instability [1], high jitter [31], high shimmer [31] high noise to

jitter [22], normal shimmer [22], high jitter [32], high shimmer [32], high variation of amplitude and f0 [22], strain [17], instability [17, 30]

is still a challenge and is missing a standardized approach.

Mixed Not reported Severity Mild to moderate Resonance disorder [3]

Severe to profound High f0 [18,25,26], instability [23,24,26,27]

Hearing loss onsetPrelingual Hoarseness [28], breathiness [28], strain [26,28], high f0 [20,25,26], high

harmonic ratio [31] Treatment Hearing aid High f0 [19,32], high pitch [10], f0 within normal standards [22], normal

Type Conductive Reduced loudness [3]

**HL characteristics Voice characteristics**

auditory monitoring of the voice [16].

implants (Table 2).

108 Update On Hearing Loss

**Table 1.** Voice characteristic of individuals with hearing loss according to type and severity of hearing loss, hearing loss onset, and treatment of choice.




**Table 2.** Overview of findings of voice characteristics when comparing hearing loss onset, treatment, and normal hearing.

#### **3.1. Perceptual ratings of the voice of individuals with hearing loss**

**Comparison Title Results**

prosthesis type on deaf children's voice

Acoustic, aerodynamic, and perceptual analyses of the voice of cochlearimplanted children [35]

Voice and pronunciation of cochlear

voice parameters within normal

An initial study of voice characteristics of children using two different sound coding strategies in comparison to normal hearing children [26]

Nasalance and nasality in children with cochlear implants and children

Normal-like motor speech parameters measured in children with long-term cochlear implant experience using a novel objective analytic technique [39]

with hearing impairment versus ageand height-matched normal hearing

Variability in voice fundamental frequency of sustained vowels in

with hearing aids [30]

implant speakers [38]

standards [24]

The influence of the auditory

quality [32]

Cochlear implant × normal hearing Cochlear implanted children present

110 Update On Hearing Loss

Hearing aid × normal hearing Laryngeal aerodynamics in children

peers [13]

hearing aided children; no significant differences in acoustic measures were

Better results for the participants with

Better voice quality for children with

Better results for the participants with

Higher instability and frequency variation for cochlear implant users.

Higher fundamental frequency, fundamental frequency variability, amplitude variability, overall severity, strain, loudness, instability, high pitch, and resonance deviation for the cochlear implanted participants

Children with hearing aids and cochlear implants showed altered nasalance. Cul-de-sac resonance was observed on a significantly larger scale than in the normal hearing group, and children with were significantly more hypernasal in than normal hearing

Cochlear implant users had poorer than normal intonation stimulability, particularly frequency variability

Significant difference in the vital capacity, maximum sustained phonation, and fast adduction

Significantly higher low frequency modulation for the individuals with

children

abduction rate

hearing loss

observed

hearing aids

cochlear implants

cochlear implants

The auditory-perceptual evaluation of the voice is a key element to understand the voice production of individuals with hearing loss. When associated with acoustics, aerodynamics, laryngeal imaging, and quality of life, it gives a complete background to define the best treatment approach. Although it is subjective and depends on listener's experience, the auditory perception is the main upholder of voice therapy, and it can be correlated to all of the assessments cited.

The voice of the individuals with hearing loss has been perceptively characterized using several scales: the Voice Profile Analysis [42], the GRBAS scale [43], the GRBASI scale [44], the Prosody-Voice Screening Profile (PVSP) [45], the Consensus Auditory-Perceptual Evaluation of Voice (CAPE-V) [46], and visual analog scales of specific parameters [47]. Theses scales 14 can be used to characterize voice quality and quantify the vocal alteration.

Reported characteristics in the last 10 years include significant overall severity of dysphonia [17, 26, 35, 48], roughness [17], strain [17, 16, 48], resonance deviations [26, 48], high pitch [1, 26], and instability [24, 26].

One particular study [21], described the voice characteristics of 40 profoundly hearingimpaired young adults using the Voice Profile Analysis (VPA), which includes articulatory (supralaryngeal) settings, laryngeal settings, strain, and prosodic settings of the voice tract. The comparison with a control group showed some interesting data for the individuals with hearing loss:


Considering these findings, the positioning, movement, and strain of the articulatory organs seem worthy of further study as they shape the voice tract and determine some aspects of voice quality.

In terms of resonance, the most reported characteristic in individuals with hearing loss is nasality. The abnormal nasalization of vowels and nasal consonants significantly contributes to the abnormal voicing of children and adults with hearing loss, which is related to poor control of the velopharyngeal valve due to the lack of auditory feedback–oral/nasal distinctions [28] and is related to the duration if the hearing impairment [2] and speech rate [27]. The velopharyngeal valve lack rhythm and strength in this population, despite normal structure and muscle activity [49].

A mixed resonance, however, is not an uncommon feature. A pharyngeal resonance also known as cul-de-sac [30, 50] can also be found and is associated with elevation of the hyoid and retraction of the tongue [51]. Hyponasality is also reported [52]. Thirty profoundly deaf children [42] had significantly higher nasalance values compared with a normal hearing control group when nasal consonants were absent (reflecting hypernasality) and significantly lower when an utterance was loaded heavily with nasal consonants (reflecting hyponasality).

The suprasegmental features of speech that are conveyed by the parameters of fundamen‐ tal frequency, intensity, and duration can directly affect the voice production and speech intelligibility. These features constitute prosody, which is considered the "melody and rhythm of spoken language" [53]. During the development of oral communication, how children acquire target appropriate prosodic structure is important because it plays a role in many aspects of linguistic function, from lexical stress to grammatical structure to emotional effect. It is therefore important for the transmission of meaning and thus for intelligibility. These aspects of the oral communication can be problematic for individuals with hearing loss since auditory monitoring is critical for listeners' recognition of proso‐ dic contrasts of speech [54]. An investigation of the production of speech intonation in cochlear implanted children in comparison with their age-matched peers with normal hearing [54] found inappropriate intonation contours for the implanted participants. Another study found that cochlear implanted children present restriction of intonation, particularly in interrogative sentences [55].

#### **3.2. Acoustic characteristics**

The acoustic analysis is an instrumental assessment that complements the auditory perceptive evaluation and provides quantitative and qualitative information about voice behavior from the analysis of the sound signal. By using computerized software, it is possible to obtain measures of fundamental frequency, perturbation and noise indexes, temporal changes in speech, and also visual graphic interpretation. This assessment magnifies the understanding of voice behavior and allows the documentation of treatment outcome.

The voice characteristics of the individual with hearing loss can be visually measured or numerically evidenced in the acoustic analysis and depend on the anatomy and physiology of the entire vocal tract. For example, the fundamental frequency can be influenced by the length, elongation, mass, and tension of the vocal folds and is integrated with the subglottic pressure. The higher fundamental frequency observed in individuals with hearing loss is related to greater tension during voice production as a result of the search for kinesthetic monitoring [41]. Also, individuals with hearing loss have difficulties in maintaining the stability of the funda‐ mental frequency [56], during the extension of a vowel and during connected speech. with the subglottic pressure. The higher fundamental frequency observed in individuals with hearing loss is related to greater tension during voice production as a result of the search for kinesthetic monitoring [41]. Also, individuals with hearing loss have difficulties in maintaining

In terms of resonance, the most reported characteristic in individuals with hearing loss is nasality. The abnormal nasalization of vowels and nasal consonants significantly contributes to the abnormal voicing of children and adults with hearing loss, which is related to poor control of the velopharyngeal valve due to the lack of auditory feedback–oral/nasal distinctions [28] and is related to the duration if the hearing impairment [2] and speech rate [27]. The velopharyngeal valve lack rhythm and strength in this population, despite normal structure

A mixed resonance, however, is not an uncommon feature. A pharyngeal resonance also known as cul-de-sac [30, 50] can also be found and is associated with elevation of the hyoid and retraction of the tongue [51]. Hyponasality is also reported [52]. Thirty profoundly deaf children [42] had significantly higher nasalance values compared with a normal hearing control group when nasal consonants were absent (reflecting hypernasality) and significantly lower when an utterance was loaded heavily with nasal consonants (reflecting hyponasality).

The suprasegmental features of speech that are conveyed by the parameters of fundamen‐ tal frequency, intensity, and duration can directly affect the voice production and speech intelligibility. These features constitute prosody, which is considered the "melody and rhythm of spoken language" [53]. During the development of oral communication, how children acquire target appropriate prosodic structure is important because it plays a role in many aspects of linguistic function, from lexical stress to grammatical structure to emotional effect. It is therefore important for the transmission of meaning and thus for intelligibility. These aspects of the oral communication can be problematic for individuals with hearing loss since auditory monitoring is critical for listeners' recognition of proso‐ dic contrasts of speech [54]. An investigation of the production of speech intonation in cochlear implanted children in comparison with their age-matched peers with normal hearing [54] found inappropriate intonation contours for the implanted participants. Another study found that cochlear implanted children present restriction of intonation,

The acoustic analysis is an instrumental assessment that complements the auditory perceptive evaluation and provides quantitative and qualitative information about voice behavior from the analysis of the sound signal. By using computerized software, it is possible to obtain measures of fundamental frequency, perturbation and noise indexes, temporal changes in speech, and also visual graphic interpretation. This assessment magnifies the understanding

The voice characteristics of the individual with hearing loss can be visually measured or numerically evidenced in the acoustic analysis and depend on the anatomy and physiology of the entire vocal tract. For example, the fundamental frequency can be influenced by the length, elongation, mass, and tension of the vocal folds and is integrated with the subglottic pressure. The higher fundamental frequency observed in individuals with hearing loss is related to greater tension during voice production as a result of the search for kinesthetic monitoring [41].

of voice behavior and allows the documentation of treatment outcome.

and muscle activity [49].

112 Update On Hearing Loss

particularly in interrogative sentences [55].

**3.2. Acoustic characteristics**

In Figure 3, the emissions of the sustained /a/ vowel by two men with 27 years of age, one with hearing loss and one with normal hearing, are presented. It is possible to visualize the greater instability in frequency (blue) and intensity (gray) and also higher fundamental frequency (203 Hz) produced by the individual with hearing loss in comparison to the individual with normal hearing (87Hz). the stability of the fundamental frequency [56], during the extension of a vowel and during connected speech. In Figure 3, the emissions of the sustained /a/ vowel by two men with 27 years of age, one with hearing loss and one with normal hearing, are presented. It is possible to visualize the greater instability in frequency (blue) and intensity (gray) and also higher fundamental frequency (203 Hz) produced by the individual with hearing loss in comparison

to the individual with normal hearing (87Hz).

counting numbers.

Figure 3. Graphs with fundamental frequency (blue) and intensity (gray) of the voices of an individual with hearing loss (A) and an individual with normal hearing (B) during the emission of a sustained vowel, obtained with the program Real Time Pitch from KayPentax. **Figure 3.** Graphs with fundamental frequency (blue) and intensity (gray) of the voices of an individual with hearing loss (A) and an individual with normal hearing (B) during the emission of a sustained vowel, obtained with the pro‐ gram Real Time Pitch from KayPentax.

Figure 3. Graphs with fundamental frequency (blue) and intensity (gray) of the voices of an individual

Figure 4 shows the excessive variation of frequency of a child with 4 years of age with hearing loss in comparison to a child with the same age and with normal hearing while counting numbers. Figure 4 shows the excessive variation of frequency of a child with 4 years of age with hearing loss in comparison to a child with the same age and with normal hearing while counting numbers. with hearing loss (A) and an individual with normal hearing (B) during the emission of a sustained vowel, obtained with the program Real Time Pitch from KayPentax. Figure 4 shows the excessive variation of frequency of a child with 4 years of age with hearing loss in comparison to a child with the same age and with normal hearing while

tridimensional graph the present the following information obtained by the Fourier transformation: the frequency in the ordinate axis, measured in Hertz; the time in the abscissa axis, measured in seconds; and the intensity, according to the degree of darkening Figure 4. Graphs with spectrograms of the sequential speech of a child with hearing loss and a child with normal hearing, obtained with the Multi Speech software from KayPentax. **Figure 4.** Graphs with spectrograms of the sequential speech of a child with hearing loss and a child with normal hear‐ ing, obtained with the Multi Speech software from KayPentax.

or coloration of the spectrum, measured in decibel [57]. tridimensional graph the present the following information obtained by the Fourier transformation: the frequency in the ordinate axis, measured in Hertz; the time in the abscissa axis, measured in seconds; and the intensity, according to the degree of darkening The acoustic evaluation can be performed visually by describing the spectrogram, a tridimen‐ sional graph the present the following information obtained by the Fourier transformation:

loss and of another with the same age and normal hearing evidence, the irregularity of the sustentation of the emission, greater presence of noise, greater spacing between the

harmonics, intensity, and effort in the voice of the woman with hearing loss.

or coloration of the spectrum, measured in decibel [57].

The acoustic evaluation can be performed visually by describing the spectrogram, a

Figure 5 shows the spectrograms of a woman with 32 years of age with hearing

connected speech.

to the individual with normal hearing (87Hz).

obtained with the program Real Time Pitch from KayPentax.

the frequency in the ordinate axis, measured in Hertz; the time in the abscissa axis, measured in seconds; and the intensity, according to the degree of darkening or coloration of the spectrum, measured in decibel [57]. Figure 4. Graphs with spectrograms of the sequential speech of a child with hearing loss and a child with normal hearing, obtained with the Multi Speech software from KayPentax. The acoustic evaluation can be performed visually by describing the spectrogram, a

with the subglottic pressure. The higher fundamental frequency observed in individuals with hearing loss is related to greater tension during voice production as a result of the search for kinesthetic monitoring [41]. Also, individuals with hearing loss have difficulties in maintaining the stability of the fundamental frequency [56], during the extension of a vowel and during

age, one with hearing loss and one with normal hearing, are presented. It is possible to visualize the greater instability in frequency (blue) and intensity (gray) and also higher fundamental frequency (203 Hz) produced by the individual with hearing loss in comparison

Figure 3. Graphs with fundamental frequency (blue) and intensity (gray) of the voices of an individual with hearing loss (A) and an individual with normal hearing (B) during the emission of a sustained vowel,

with hearing loss in comparison to a child with the same age and with normal hearing while

Figure 4 shows the excessive variation of frequency of a child with 4 years of age

In Figure 3, the emissions of the sustained /a/ vowel by two men with 27 years of

Figure 5 shows the spectrograms of a woman with 32 years of age with hearing loss and of another with the same age and normal hearing, evidencing greater irregularity of the susten‐ tation of the emission, greater presence of noise, greater spacing between the harmonics, intensity, and effort in the voice of the woman with hearing loss. tridimensional graph the present the following information obtained by the Fourier transformation: the frequency in the ordinate axis, measured in Hertz; the time in the abscissa axis, measured in seconds; and the intensity, according to the degree of darkening or coloration of the spectrum, measured in decibel [57]. Figure 5 shows the spectrograms of a woman with 32 years of age with hearing loss and of another with the same age and normal hearing evidence, the irregularity of the

harmonics, intensity, and effort in the voice of the woman with hearing loss.

sustentation of the emission, greater presence of noise, greater spacing between the

**Figure 5.** Graphs with spectrograms of the sustained vowel of a woman with hearing loss (A) and a woman with nor‐ mal hearing (B) obtained with the Multi Speech program from KayPentax.

Some perturbations of the sound wave and of the ratio of noise in relation to the harmonics were used by some authors to characterize the voice of individuals with hearing loss. These characteristics can be related to the perception of roughness and strain in the voice. Generally, the voices of individuals with hearing loss show more perturbation of the sound wave and greater quantity of noise in relation to individuals with normal hearing [58]. Among the measures of perturbation, the jitter indicates short-term variability of the fundamental frequency. These values can represent a small variation in mass or tension of the vocal folds, on the distribution of mucus on them, on the symmetry of the structures, or even in the muscular or neural activity involved; the shimmer indicates short-term variability of the amplitude of the sound wave, and it is a measure of phonatory stability. Its values increase as the amount of noise in the emission increases [59]. The noise-to-harmonic ratio measures the relative quantity of additional noise in the voice signal, which can be generated by the turbulence of the airflow in the glottis in cases of incomplete closure during phonation or also result from aperiodic vibration of the vocal folds [60], being associated with the presence of roughness. One of the limitations of this form of acoustic analysis is that, to perform a reliable analysis of jitter, shimmer, and noise measures, the sound signal cannot be too altered. This analysis is only reliable in normal or slightly altered voices, which prevents the evaluation of voices with more severe alterations.

#### **3.3. Laryngeal features**

the frequency in the ordinate axis, measured in Hertz; the time in the abscissa axis, measured in seconds; and the intensity, according to the degree of darkening or coloration of the

a child with normal hearing, obtained with the Multi Speech software from KayPentax.

harmonics, intensity, and effort in the voice of the woman with hearing loss.

with the subglottic pressure. The higher fundamental frequency observed in individuals with hearing loss is related to greater tension during voice production as a result of the search for kinesthetic monitoring [41]. Also, individuals with hearing loss have difficulties in maintaining the stability of the fundamental frequency [56], during the extension of a vowel and during

age, one with hearing loss and one with normal hearing, are presented. It is possible to visualize the greater instability in frequency (blue) and intensity (gray) and also higher fundamental frequency (203 Hz) produced by the individual with hearing loss in comparison

Figure 3. Graphs with fundamental frequency (blue) and intensity (gray) of the voices of an individual with hearing loss (A) and an individual with normal hearing (B) during the emission of a sustained vowel,

with hearing loss in comparison to a child with the same age and with normal hearing while

Figure 4 shows the excessive variation of frequency of a child with 4 years of age

Figure 4. Graphs with spectrograms of the sequential speech of a child with hearing loss and

The acoustic evaluation can be performed visually by describing the spectrogram, a

Figure 5 shows the spectrograms of a woman with 32 years of age with hearing

In Figure 3, the emissions of the sustained /a/ vowel by two men with 27 years of

Figure 5 shows the spectrograms of a woman with 32 years of age with hearing loss and of another with the same age and normal hearing, evidencing greater irregularity of the susten‐ tation of the emission, greater presence of noise, greater spacing between the harmonics,

A B

**Figure 5.** Graphs with spectrograms of the sustained vowel of a woman with hearing loss (A) and a woman with nor‐

Some perturbations of the sound wave and of the ratio of noise in relation to the harmonics were used by some authors to characterize the voice of individuals with hearing loss. These characteristics can be related to the perception of roughness and strain in the voice. Generally, the voices of individuals with hearing loss show more perturbation of the sound wave and greater quantity of noise in relation to individuals with normal hearing [58]. Among the measures of perturbation, the jitter indicates short-term variability of the fundamental frequency. These values can represent a small variation in mass or tension of the vocal folds, on the distribution of mucus on them, on the symmetry of the structures, or even in the muscular or neural activity involved; the shimmer indicates short-term variability of the amplitude of the sound wave, and it is a measure of phonatory stability. Its values increase as the amount of noise in the emission increases [59]. The noise-to-harmonic ratio measures the relative quantity of additional noise in the voice signal, which can be generated by the turbulence of the airflow in the glottis in cases of incomplete closure during phonation or also result from aperiodic vibration of the vocal folds [60], being associated with the presence of roughness. One of the limitations of this form of acoustic analysis is that, to perform a reliable analysis of jitter, shimmer, and noise measures, the sound signal cannot be too altered. This analysis is only reliable in normal or slightly altered voices, which prevents the evaluation of

tridimensional graph the present the following information obtained by the Fourier transformation: the frequency in the ordinate axis, measured in Hertz; the time in the abscissa axis, measured in seconds; and the intensity, according to the degree of darkening

loss and of another with the same age and normal hearing evidence, the irregularity of the sustentation of the emission, greater presence of noise, greater spacing between the

intensity, and effort in the voice of the woman with hearing loss.

or coloration of the spectrum, measured in decibel [57].

mal hearing (B) obtained with the Multi Speech program from KayPentax.

voices with more severe alterations.

spectrum, measured in decibel [57].

connected speech.

counting numbers.

114 Update On Hearing Loss

to the individual with normal hearing (87Hz).

obtained with the program Real Time Pitch from KayPentax.

Based on perceptual and acoustic data, many authors [3, 17, 33, 35, 61] state that individuals with hearing loss have difficulties in controlling the laryngeal function. To this date, however, laryngeal characteristics of individuals with hearing loss have not been thoroughly studied.

It has been stated that the larynx of a hearing-impaired child usually shows no anatomic or physiological abnormalities in the first years of life, but lack of auditory feedback can result in discoordination of intrinsic and extrinsic laryngeal muscles and disturbed contraction and relaxation of antagonistic muscles [13].

Inadequate laryngeal activity of four normally hearing and four hearing-impaired persons was found during productions of word-initial voiced and voiceless consonants with a flexible fiberoptic laryngoscope [62]. Three of the hearing-impaired subjects exhibited greater variability than their normally hearing peers in terms of the degree and duration of vocal fold abduction during voiceless consonant productions, but only one exhibited excessively wide glottal openings, suggesting that deaf persons waste air during speech production.

A study [63] was conducted with two normal hearing adults and four adults with profound hearing loss using high speed laryngeal film and acoustic data. The authors used the vowelconsonant-vowel segment "aha." The study found that two of the hearing-impaired subjects did not exhibit glottal waveforms in vowel production, which differed substantially from those of the normally hearing subjects. However, one subject with hearing loss exhibited maximal glottal openings approximately double those of the other subjects and large cycle-to-cycle variability. The most dramatic differences observed between the normally hearing and hearing-impaired subjects were the duration and the magnitude of the abductory gestures associated with devoicing. The vocal fold abductory-adductory movements associated with the devoiced segments appeared to be discontinuous in nature, which was characterized by abrupt abductory movement following the first vowel, which frequently reached a plateau before adductory movement associated with the second vowel. Such laryngeal features can result in abnormal voice production; however, these laryngeal findings were not correlated to voice quality.

#### **3.4. Voice-related quality of life**

The instruments used to measure quality of life in health sciences allow the understanding of the impact of a condition through patient perception. These materials have been used to obtain a multidimensional assessment of the human being. Patient-based assessment can be used to compose the evaluation process, helps clinicians to select strategies for rehabilitation based on specifics indentified, and monitors treatment outcomes [64].

With the inclusion of quality of life analysis in the health sciences, voice-related quality of life protocols were created since protocols about general health are not ideal to assess patients with voice disorders. Due to the importance of human communication in the several domains that contribute to quality of life, these instruments investigate if there are physical, emotional, and social limitations related to voice disorders, including the use of professional voice [65].

These instruments, therefore, contribute to the knowledge of the impact of the communication disorders manifested by the voice alteration. The extensive list of voice problems the individ‐ uals with hearing loss can affect their quality of life. However, the protocols of voice-related quality of life already developed are not entirely adequate to the voice problems frequently presented by individuals with hearing loss, and voice-related quality of life in individuals with hearing loss has not yet been thoroughly studied.

A single study [4] investigated voice-related quality of life in this population by comparing the scores of the Voice Handicap Index [66] between adults with moderate to profound hearing loss and their normal peers. There were significant differences in the total score and in the score of all three domains: functional, physical, and emotional. However, there was a major variability of responses obtained in the group of patients with hearing loss (a variation of 94 points) so the authors were not able to define a VHI score range.

Also, the several protocols of quality of life related to the presence of hearing loss or use of hearing aids [67–69] approach communication aspects regarding sound reception and not regarding the difficulties of voice and speech production, even though it is common knowl‐ edge that hearing interferes also in the emission stage of the communicative process.

### **4. Voice training in individuals with hearing loss**

The auditory rehabilitation aims to allow deaf individuals using devices such as heading aids and cochlear implants to develop auditory abilities and oral communication. However, since voice characteristics commonly found in individuals with hearing loss can greatly compromise oral communication, voice training in addition to hearing, language, and speech rehabilitation is essential to restore normal physiology. For both prelingually deafened children and postlingually deafened adults, intervention can improve voice quality and prevent the development of abnormal voice production. Depending on the findings of the voice assess‐ ment, the treatment can include techniques for respiration, posture, movement of the articu‐ lators, vertical laryngeal excursion, loudness, and resonance [70].

The speech and language rehabilitation program of the Brasilia Teaching Hospital (Hospital Universitário de Brasília [HUB]) provides treatment for children, adolescents, and adults with moderate to profound hearing loss who are users of hearing aids and/or cochlear implants. The purpose of the therapy goes beyond speech perception. In the therapeutic plan, voice training is considered an element just as important as auditory training, being considered therefore a part of the extensive process of rehabilitation of individuals with hearing loss.

Voice training comprises many approaches: the universal methods that change voice quality as a whole and the specific techniques that rely on laryngeal imaging and aim to work with specific groups of muscles. With the use of different techniques and exercises, it is possible to modify the voice by acting on the muscle activity of the vocal tract, to enhance the relationship of the three subsystems of voice production (respiration, phonation, and resonance), and to demonstrate to the patient the many possibilities of motor adjustments of voice production [57]. Based on the findings of the voice assessment and on laryngeal imaging whenever possible, the clinician can select a number of voice exercises that are thoroughly described in the literature [50, 71] to improve the abnormalities found. Some of the exercises suggested for hearing-impaired individuals are the prolonged /b/ exercise, manual circumlaryngeal massage associated with the emission of vowels and words, emissions of the closed vowels /o/ and /u/ while flexing the head to fix the larynx in a lower position, chewing, and lip vibration [72, 73]. In Table 3, some exercises for voice treatment [50, 71] are suggested based on findings of voice characteristics of individuals with hearing loss reported in the literature.

These instruments, therefore, contribute to the knowledge of the impact of the communication disorders manifested by the voice alteration. The extensive list of voice problems the individ‐ uals with hearing loss can affect their quality of life. However, the protocols of voice-related quality of life already developed are not entirely adequate to the voice problems frequently presented by individuals with hearing loss, and voice-related quality of life in individuals with

A single study [4] investigated voice-related quality of life in this population by comparing the scores of the Voice Handicap Index [66] between adults with moderate to profound hearing loss and their normal peers. There were significant differences in the total score and in the score of all three domains: functional, physical, and emotional. However, there was a major variability of responses obtained in the group of patients with hearing loss (a variation of 94

Also, the several protocols of quality of life related to the presence of hearing loss or use of hearing aids [67–69] approach communication aspects regarding sound reception and not regarding the difficulties of voice and speech production, even though it is common knowl‐

The auditory rehabilitation aims to allow deaf individuals using devices such as heading aids and cochlear implants to develop auditory abilities and oral communication. However, since voice characteristics commonly found in individuals with hearing loss can greatly compromise oral communication, voice training in addition to hearing, language, and speech rehabilitation is essential to restore normal physiology. For both prelingually deafened children and postlingually deafened adults, intervention can improve voice quality and prevent the development of abnormal voice production. Depending on the findings of the voice assess‐ ment, the treatment can include techniques for respiration, posture, movement of the articu‐

The speech and language rehabilitation program of the Brasilia Teaching Hospital (Hospital Universitário de Brasília [HUB]) provides treatment for children, adolescents, and adults with moderate to profound hearing loss who are users of hearing aids and/or cochlear implants. The purpose of the therapy goes beyond speech perception. In the therapeutic plan, voice training is considered an element just as important as auditory training, being considered therefore a part of the extensive process of rehabilitation of individuals with hearing loss.

Voice training comprises many approaches: the universal methods that change voice quality as a whole and the specific techniques that rely on laryngeal imaging and aim to work with specific groups of muscles. With the use of different techniques and exercises, it is possible to modify the voice by acting on the muscle activity of the vocal tract, to enhance the relationship of the three subsystems of voice production (respiration, phonation, and resonance), and to demonstrate to the patient the many possibilities of motor adjustments of voice production

edge that hearing interferes also in the emission stage of the communicative process.

hearing loss has not yet been thoroughly studied.

116 Update On Hearing Loss

points) so the authors were not able to define a VHI score range.

**4. Voice training in individuals with hearing loss**

lators, vertical laryngeal excursion, loudness, and resonance [70].


**Table 3.** Common voice alterations in individuals with hearing loss and the respective techniques and exercises suggested in the voice rehabilitation.

Naturally, adapting the conventional voice therapy is very helpful, especially for people with severe to profound hearing loss since the training should not rely exclusively in auditory monitoring. Among the methods used for hearing rehabilitation is the multisensory method that uses the auditory channel, the visual channel, and tactile/kinesthetic cues [74, 75]. In the voice clinic, the use of visual, kinesthetic, and proprioceptive cues is extremely useful to develop parameters such as frequency and intensity [71], which is due to the fact that visual and tactile/kinetic feedbacks of the vocal apparatus are preserved in this population and should be explored in addition to the auditory training [70]. Abilities such as lip reading exemplify the use of visual cues for the development of speech and voice [72].

**Figure 6.** Examples of visual feedback in voice training. (A) Real-time spectrogram (GRAM 5.1.6). (B) Real-time moni‐ toring of voice signal following a model provided in the upper window (Real Time Pitch, KayPentax). (C) Real-time monitoring of frequency and intensity. (D) Nasal mirror and for monitoring nasal airflow. (E) Scape-scope for monitor‐ ing nasal airflow. (F) Visual monitoring of intensity (Voice Games, KayPentax).

Using visual cues, it is possible to monitor adequate frequency and intensity with established thresholds, noise, voice attacks, strain, instability, formants, and voicing. Such methods are considered effective in the voice rehabilitation of deaf individuals [76, 77]. Studies found improved frequency control, respiratory support, intelligibility, jitter and shimmer after voice therapy with computerized visual feedback [72, 78], and reduced nasality using visual cues to monitor nasal airflow [79, 80]. These cues include spectrograms, diagrams, nasal mirror, scapescope, and even computerized software for children to promote a playful environment while training voice production (Figures 6A–6F).

develop parameters such as frequency and intensity [71], which is due to the fact that visual and tactile/kinetic feedbacks of the vocal apparatus are preserved in this population and should be explored in addition to the auditory training [70]. Abilities such as lip reading

A B

C D

E F

**Figure 6.** Examples of visual feedback in voice training. (A) Real-time spectrogram (GRAM 5.1.6). (B) Real-time moni‐ toring of voice signal following a model provided in the upper window (Real Time Pitch, KayPentax). (C) Real-time monitoring of frequency and intensity. (D) Nasal mirror and for monitoring nasal airflow. (E) Scape-scope for monitor‐

Using visual cues, it is possible to monitor adequate frequency and intensity with established thresholds, noise, voice attacks, strain, instability, formants, and voicing. Such methods are

ing nasal airflow. (F) Visual monitoring of intensity (Voice Games, KayPentax).

exemplify the use of visual cues for the development of speech and voice [72].

118 Update On Hearing Loss

The tactile/kinesthetic monitoring is harder to develop. Patients must identify proprioceptive symptoms and sensations that indicate abnormal voice production such as tightness, presence of secretion, pain, dryness, discomfort, etc. The procedure for using these cues include emission while touching the head, forehead, face, and resonance cavities, including the nose, neck, and thorax [71] (Figures 7A–7B).

**Figure 7.** Examples of kinesthetic feedback in voice training. (A) Hands feeling resonators for resonance control. (B) Monitoring larynx decent for normalizing pitch.

A structured voice therapy program for individual with hearing loss was described [78] and consisted of 16 therapy sessions, conducted twice a week with the duration of 1h. In the first half of the therapy session, the participants performed specific vocal exercises, which consisted of tongue snapping, tongue or lip vibration, humming, fricative sounds, prolonged /b/ exercise, vocal fry, overarticulation, chewing exercise, chanting, and visual/proprioceptive monitoring. In the second half, computerized games were used to provide visual feedback for monitoring frequency and intensity during speech tasks. The program showed promising results in speech and voice using these techniques and exercises. A similar approach was later suggested [72] using mainly visual feedback with computerized games and also finding improvement in speech and voice production.

A case study is presented to illustrate the immediate results of voice training during a therapy session of a young adult with profound hearing loss that use a unilateral cochlear implant. The patient is a 26-year-old male, with bilateral profound hearing loss due to bacterial meningitis at the age of 23 years.

To compare the results of the voice exercises, the prolonged /a/ vowel and a sample of sequential speech (counting from 1 to 10) were recorded pre- and post-therapy session. The perceptive analysis of the /a/ vowel pre-therapy evidenced brusque vocal attack, roughness, nasality, and instability. The sequential speech evidenced roughness, nasality, and imprecise articulation. The purpose of the voice exercises was to reduce laryngeal strain, to reduce nasality and cul-de-sac resonance improving relationship between glottal source and reso‐ nance, and to enhance articulation.

The selected exercises were as follows:


After the therapy session, there was a significant reduction of the brusque voice attack, roughness, and nasality in both emissions. In Table 4, some acoustics parameters of the /a/ vowel are presented pre- and post-therapy session using the Multi Dimensional Voice Program (MDVP, KayPentax). There was a slight reduction in fundamental frequency, although it is within normal standards for men at this age. There was also reduction of short- term variation (jitter) and long-term variation of frequency (jitter), short-term (shimmer) and long-term variation of amplitude (vAm), and reduction of the noise to harmonic ratio (NHR).


**Table 4.** Acoustic parameters of the /a/ vowel pre- and post-therapy session.

In Figure 8, the narrowband spectrogram of the pre-therapy /a/ vowel shows brusque voice attack, presence of subharmonics, low high-frequency harmonics, and instability. In the posttherapy spectrogram, increase in high-frequency harmonics, reduction of brusque voice attack, reduction of subharmonics, and reduction of instability are observed.

Figure 9 shows the narrowband spectrogram of the sequential speech using the Multi Speech Main Program (KayPentax), on which a significant increase of harmonics can be observed, although there is presence of subharmonics in both emissions.

observed.

perceptive analysis of the /a/ vowel pre-therapy evidenced brusque vocal attack, roughness, nasality, and instability. The sequential speech evidenced roughness, nasality, and imprecise articulation. The purpose of the voice exercises was to reduce laryngeal strain, to reduce nasality and cul-de-sac resonance improving relationship between glottal source and reso‐

**•** Chewing exercise associated with sequential speech (numbers from 1 to 10, months of the

After the therapy session, there was a significant reduction of the brusque voice attack, roughness, and nasality in both emissions. In Table 4, some acoustics parameters of the /a/ vowel are presented pre- and post-therapy session using the Multi Dimensional Voice Program (MDVP, KayPentax). There was a slight reduction in fundamental frequency, although it is within normal standards for men at this age. There was also reduction of short- term variation (jitter) and long-term variation of frequency (jitter), short-term (shimmer) and long-term

**Parameter Pre-therapy Post-therapy**

variation of amplitude (vAm), and reduction of the noise to harmonic ratio (NHR).

Average fundamental frequency (f0) 127.052 123.322 Jitter (%) 3.966 3.337 Fundamental frequency variation (vF0) 3.652 3.247 Shimmer (%) 5.590 4.176 Peak to peak amplitude variation (vAm) 14.535 9.725 Noise to harmonic ratio (NHR) 0.214 0.147

In Figure 8, the narrowband spectrogram of the pre-therapy /a/ vowel shows brusque voice attack, presence of subharmonics, low high-frequency harmonics, and instability. In the posttherapy spectrogram, increase in high-frequency harmonics, reduction of brusque voice attack,

Figure 9 shows the narrowband spectrogram of the sequential speech using the Multi Speech Main Program (KayPentax), on which a significant increase of harmonics can be observed,

**Table 4.** Acoustic parameters of the /a/ vowel pre- and post-therapy session.

reduction of subharmonics, and reduction of instability are observed.

although there is presence of subharmonics in both emissions.

**•** Chanting the sequence "mananha, menenhe, mininhi, mononho, mununhu"

nance, and to enhance articulation.

**•** Humming

120 Update On Hearing Loss

**•** Chewing exercise

year, days of the week)

The selected exercises were as follows:

**•** Humming associated with vowels

#### Fundamental frequency variation (vF0) 3.652 3.247

In Figure 8, the narrowband spectrogram of the pre-therapy /a/ vowel shows

brusque voice attack, presence of subharmonics, low high-frequency harmonics, and instability. In the post-therapy spectrogram, increase in high-frequency harmonics, reduction

Parameter Pre-therapy Post-therapy

Figure 9 shows the narrowband spectrogram of the sequential speech using the

Multi Speech Main Program (KayPentax), on which a significant increase of harmonics can

the /a/ vowel are presented pre- and post-therapy session using the Multi Dimensional Voice Program (MDVP, KayPentax). There was a slight reduction in fundamental frequency, although it is within normal standards for men at this age. There was also reduction of shortterm variation (jitter) and long-term variation of frequency (jitter), short-term (shimmer) and long-term variation of amplitude (vAm), and reduction of the noise to harmonic ratio (NHR).

Table 4. Acoustic parameters of the /a/ vowel pre- and post-therapy session.

the /a/ vowel are presented pre- and post-therapy session using the Multi Dimensional Voice Program (MDVP, KayPentax). There was a slight reduction in fundamental frequency, although it is within normal standards for men at this age. There was also reduction of shortterm variation (jitter) and long-term variation of frequency (jitter), short-term (shimmer) and long-term variation of amplitude (vAm), and reduction of the noise to harmonic ratio (NHR).

Average fundamental frequency (f0) 127.052 123.322 Jitter (%) 3.966 3.337 Fundamental frequency variation (vF0) 3.652 3.247 Shimmer (%) 5.590 4.176 Peak to peak amplitude variation (vAm) 14.535 9.725 Noise to harmonic ratio (NHR) 0.214 0.147

Average fundamental frequency (f0) 127.052 123.322 Jitter (%) 3.966 3.337

Multi Speech Main Program (KayPentax), on which a significant increase of harmonics can be observed, although there is presence of subharmonics in both emissions. Figure 9 shows the narrowband spectrogram of the sequential speech using the **Figure 8.** Spectrogram of the /a/ vowel pre- and post-therapy session.

 This particulate case study showed that voice training was helpful to improve voice **Figure 9.** Spectrogram of the sequential speech pre- and post-therapy session.

Figure 9. Spectrogram of the sequential speech pre- and post-therapy session.

Figure 8. Spectrogram of the /a/ vowel pre- and post-therapy session.

characteristics of this individual improved significantly, and the most prominent features were improvement of resonance and instability. **Conclusions** The primary difficulties of children and adults with hearing loss are related to auditory abilities and language development, and with reason, they become the primary This particulate case study showed that voice training was helpful to improve voice production and consequently oral communication. The acoustic and perceptual characteristics of this individual improved significantly, and the most prominent features were improvement of resonance and instability. Figure 9. Spectrogram of the sequential speech pre- and post-therapy session.

center of attention in the rehabilitation process. However, voice abnormalities should not be overlooked since they can greatly compromise voice quality and speech intelligibility. There

production and consequently oral communication. The acoustic and perceptual

#### is still much to be done in this area of expertise. The understanding of laryngeal behavior, **5. Conclusions**

The primary difficulties of children and adults with hearing loss are related to auditory abilities and language development, and with reason, they become the primary center of attention in the rehabilitation process. However, voice abnormalities should not be overlooked since they can greatly compromise voice quality and speech intelligibility. There is still much to be done in this area of expertise. The understanding of laryngeal behavior, acoustic and perceptual characteristics, voice-related quality of life, and an effective implementation of voice training in the process of rehabilitation is crucial. In adequate proportions, vocal rehabilitation should take place along with the auditory training and oral language development since the very beginning of treatment so that individuals with hearing loss can achieve intelligible, pleasant, and socially acceptable oral communication, maintaining correct function of respiration, phonation, articulation, and resonance.

#### **Author details**

Ana Cristina Coelho1\*, Daniela Malta Medved1 and Alcione Ghedini Brasolotto2

\*Address all correspondence to: anacrisccoelho@yahoo.com.br

1 Brasília Teaching Hospital, University of Brasília, Brasília-DF, Brazil

2 Department of Speech-Language and Audiology, Bauru School of Dentistry, University of São Paulo, Bauru-SP, Brazil

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2 Department of Speech-Language and Audiology, Bauru School of Dentistry, University of

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1 Brasília Teaching Hospital, University of Brasília, Brasília-DF, Brazil

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128 Update On Hearing Loss

**Hearing Impairment in Professional Musicians and Industrial Workers — Profession-Specific Auditory Stimuli Used to Evoke Event-Related Brain Potentials and to Show Different Auditory Perception and Processing**

Edeltraut Emmerich, Marcus Engelmann, Melanie Rohmann and Frank Richter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/61137

#### **Abstract**

Hearing impaired professional musicians or industrial workers often report that they were able to identify mistuned chords in a music piece or even slight changes in the noise of their machines (usually > 100 dB SPL) though they were handicapped in listening tasks in daily routine.

In order to assess central processing of acoustic stimuli, we analyzed auditory evoked potentials (AEP) and EEG spectra after stimulation with work-related auditory stimuli in healthy controls, in hearing impaired musicians or hearing impaired workers from the beverage industry. Stimuli were series of in-tune or mistuned synthetic piano chords or the original machine noise the workers heard in daily routine and the same noise with disturbing signals.

Professional musicians identified the mistuned stimuli and the AEP differed significantly. The workers recognized the disturb signals. In both groups the spectral analysis confirmed a frequency shift towards higher alpha frequencies and an altered spatial distribution of the EEG frequencies during presentation of the disturb signals.

We assume that professionalism causes learning of typical auditory stimuli that is important for auditory processing after hearing impairment. AEP component analysis

© 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

and spectral analysis of the EEG are important tools to objectify this processing, in particular in hearing impaired employees.

**Keywords:** Auditory evoked potential, Mismatch negativity (MMN), Hearing impair‐ ment, Permanent threshold shift (PTS), Occupational disease

#### **1. Introduction**

The mismatch negativity component (MMN) of auditory evoked event-related potential can be elicited by deviant stimuli inserted into a follow-up of identical sounds [1]. See for review [2]. In the past, numerous studies had been performed in which changed attributes of the stimuli, such as decrement in duration [3], changes in frequency [4], or changed stimulus intensity [5], were used to differentiate between standard and deviant stimuli. MMN to musical stimuli has been investigated for a long time. It was shown that MMN was caused by a timbre change [6,7]. In a later study, it was shown [8] that comparison of MMN to omitted tones in a series of sine-wave tone pips could be used to differentiate between musicians and nonmusicians. Violation of harmony rules elicited large MMN in the fronto-central cortex areas [9]. Slightly mistuned chords produced MMN in professional violinists, but not in nonmusicians [10]. Similarly, larger and earlier MMN to rhythm variations were observed in jazz musicians than in non-musicians [11].

An earlier study of our group raised the issue that hearing-impaired professional musicians were able to play their instruments in the orchestras and to perform without problems when they were trained for years, regardless of their permanent threshold shift (PTS) [12]. Interest‐ ingly, those musicians reported on hearing problems when watching TV or if they wanted to have conversation in a noisy environment (party-noise effect). To our knowledge, there are only few studies about musicians dealing with the effects of occupational noise and central compensation after hearing damage. Therefore, we want to test whether differences exist in auditory event-related potentials (AEP) (amplitudes and latencies) and/or in MMN reflecting the sound processing while comparing normal hearing people and musicians (normal hearing and hearing impaired). The new aspect in our study is the use of typical musical stimuli, i.e., in-tune and mistuned chords. We assumed that professional musicians should be trained to these stimuli regardless whether they have normal hearing or not.

There is some evidence for the assumption that ongoing training of professional musicians would produce changes in the central processing of musical auditory signals since an earlier study did not find different neural generators for MMN while comparing musicians and nonmusicians, but found typical differences in MMN between both groups after omitted tone pips [8]. From other data, it was supposed that ongoing professional training could result in a more accurate tuning of frequency-specific neurons in musicians [10]. Professional musicians are considered to be a model for cortical plasticity caused by ongoing musical training [13-17]. In a review [18], it was summarized that top-down and bottom-up plasticity exists in the auditory cortex, as well as in other somatosensory areas of the brain. This was supported by a recent study [19] that showed that the posterior medial cortex is involved in processing of melodic and harmonic information. If ongoing musical training participates in this process, it would be interesting to see whether a hearing deficit in trained professional musicians would interfere with, e.g., an improved tuning function or with the recognition of wrongly tuned sounds.

The present experiments investigated whether MMN could be detected in professional musicians, non-musicians, or industrial workers without formal musical training when typical musical stimuli (C-chords) were presented in the oddball-design. To get better information over the whole range of audibility, we applied the stimuli both in the mid-frequency and in the high-frequency range. We analyzed the amplitudes and latencies of the first positive and negative components of the AEP. We looked further for differences in the MMN between the three investigated groups. In another series of experiments, we tested with the same paradigm, whether MMN to mistuned high-frequency stimuli could still be observed in hearing-impaired professional musicians with a PTS in the high-frequency range between 3.000 Hz and 8.000 Hz. To evaluate to what extent the subjects were annoyed by the mistuned chords, we analyzed the EEG frequency activity in the interstimulus intervals and additionally looked for changes in heart frequency. To check, whether a long-lasting professional training might have induced a learning process for specific sounds, we repeated the EEG and heart frequency analysis in the group of hearing-impaired workers and presented them slightly disturbed machine noise they usually had heard in their daily working routine.

#### Hypotheses:

and spectral analysis of the EEG are important tools to objectify this processing, in

**Keywords:** Auditory evoked potential, Mismatch negativity (MMN), Hearing impair‐

The mismatch negativity component (MMN) of auditory evoked event-related potential can be elicited by deviant stimuli inserted into a follow-up of identical sounds [1]. See for review [2]. In the past, numerous studies had been performed in which changed attributes of the stimuli, such as decrement in duration [3], changes in frequency [4], or changed stimulus intensity [5], were used to differentiate between standard and deviant stimuli. MMN to musical stimuli has been investigated for a long time. It was shown that MMN was caused by a timbre change [6,7]. In a later study, it was shown [8] that comparison of MMN to omitted tones in a series of sine-wave tone pips could be used to differentiate between musicians and nonmusicians. Violation of harmony rules elicited large MMN in the fronto-central cortex areas [9]. Slightly mistuned chords produced MMN in professional violinists, but not in nonmusicians [10]. Similarly, larger and earlier MMN to rhythm variations were observed in jazz

An earlier study of our group raised the issue that hearing-impaired professional musicians were able to play their instruments in the orchestras and to perform without problems when they were trained for years, regardless of their permanent threshold shift (PTS) [12]. Interest‐ ingly, those musicians reported on hearing problems when watching TV or if they wanted to have conversation in a noisy environment (party-noise effect). To our knowledge, there are only few studies about musicians dealing with the effects of occupational noise and central compensation after hearing damage. Therefore, we want to test whether differences exist in auditory event-related potentials (AEP) (amplitudes and latencies) and/or in MMN reflecting the sound processing while comparing normal hearing people and musicians (normal hearing and hearing impaired). The new aspect in our study is the use of typical musical stimuli, i.e., in-tune and mistuned chords. We assumed that professional musicians should be trained to

There is some evidence for the assumption that ongoing training of professional musicians would produce changes in the central processing of musical auditory signals since an earlier study did not find different neural generators for MMN while comparing musicians and nonmusicians, but found typical differences in MMN between both groups after omitted tone pips [8]. From other data, it was supposed that ongoing professional training could result in a more accurate tuning of frequency-specific neurons in musicians [10]. Professional musicians are considered to be a model for cortical plasticity caused by ongoing musical training [13-17]. In a review [18], it was summarized that top-down and bottom-up plasticity exists in the auditory cortex, as well as in other somatosensory areas of the brain. This was supported by a recent

particular in hearing impaired employees.

**1. Introduction**

132 Update On Hearing Loss

musicians than in non-musicians [11].

ment, Permanent threshold shift (PTS), Occupational disease

these stimuli regardless whether they have normal hearing or not.


### **2. Materials and methods**

#### **2.1. Proband groups**

#### **Normal hearing and hearing-impaired non-musicians, aged 16 to 30 years**

A group consisting of 16 members of the Medical Faculty of Jena (mean age 21.3 years) who had no hearing deficits, and who did not perform music regularly and never had formal training in music was categorized as non-musicians. The participants were all right-handed. The hearing-impaired group (10 age-matched participants) had a hearing deficit (PTS) of about 20 dB SPL in the frequency range from 3.000 Hz to 8.000 Hz.

#### **Normal hearing and hearing-impaired professional musicians, aged 28 to 68 years**

In this part of the study participated 15 professional normal hearing musicians (mean age 41.4 years) who were employed at three German orchestras. The instrument groups were violins, trombones, oboes, bassoons, cellos, violas, and contrabasses. A second group of 10 professional musicians from the same three orchestras (mean age 48.1 years) had a hearing deficit (PTS) of more than 30 dB in frequencies larger 3 kHz. These 10 musicians played violins, contrabasses, bassoon, cello, trombones, and oboe.

#### **Hearing-impaired industrial workers, aged 38 to 63 years**

In this part of the study participated 20 industrial workers from a brewery who worked on bottle washing or bottle filling machines. Their hearing loss (PTS) of more than 20 dB SPL in the frequency range from 3.000 Hz to 8.000 Hz was officially recognized as an occupational disease. The workers were aged 38 to 63 years and had never had formal musical training or played any kind of music. All experiments were performed without hearing aids.

#### **2.2. Study design**

The study was approved by the local ethics committee of the University of Jena. All participants gave informed consent to this study and received monetary compensation for their participa‐ tion. In a questionnaire, the participants were asked for their age; musical experiences, i.e., duration of employment in the orchestra or attending music school, instruments that are or were played, duration of training time per week, and the use of hearing protectors; occurrence of tinnitus; occurrence of ear, nose, and throat diseases; and hereditary ear diseases in the family. We also asked for noisy leisure time activities. The workers were asked similar questions with special respect for noise exposition per working shift. The hearing ability of the right and left ears in each participant was tested by means of a high frequency audiometer (Grahnert Präcitronic MA 22; Dresden, Germany, combined with a headphone HDA-200; Sennheiser, Hannover, Germany) and by measuring the otoacoustic emissions (DPOAE/ TEOAE) (Madsen, Denmark). Details were given by our group in the literature [12].

To study the perception of auditory stimuli, we recorded MMN using the classical ac-EEG technique. Participants were seated comfortably with closed eyes. They listened to the stimuli that were presented via loudspeakers in the free field mode and were instructed only to listen relaxed and to avoid attention or any reaction to the stimuli to minimize artifacts caused by movements.

The ac-EEG was recorded from 32 electrodes (Figure 1) positioned according to the interna‐ tional 10/20 system over frontal, central, temporal and parietal brain areas of both hemispheres using the standardized Easy-Cap device (Easy Cap GmbH, Herrsching-Breitbrunn, Germany). A linked-mastoid electrode served as a reference. Impedance was maintained below 5 kOhm. An electrode at the forehead was used as a ground. The electrooculogram was recorded for rejection of artifacts (two electrodes above and below the eye, one electrode lateral to the eye). The EEG was recorded with the Brain Products recording system (Brain Products GmbH, Gilching, Germany). The bandpass ranged from 0.1 Hz to 250 Hz. The amplified signals were digitized at a 5.000 Hz sample rate and analyzed off-line. The electrocardiogram was recorded for a beat-to-beat frequency analysis.

**Figure 1.** The left panel shows the typical electrode positions at the cap that were used in this study. Two additional reference electrodes were placed at the mastoids and as a ground electrode, the FPC position was used. To extract arti‐ facts by eye movements, the VEOG was recorded with two electrodes. For analyzing the heart rate, the electrocardio‐ gram in the Einthoven triangle was recorded (symbolized by the ECG marking). The right panel shows the Easy Cap device on the head while fixing the electrodes.

#### **2.3. Auditory stimuli**

The hearing-impaired group (10 age-matched participants) had a hearing deficit (PTS) of about

In this part of the study participated 15 professional normal hearing musicians (mean age 41.4 years) who were employed at three German orchestras. The instrument groups were violins, trombones, oboes, bassoons, cellos, violas, and contrabasses. A second group of 10 professional musicians from the same three orchestras (mean age 48.1 years) had a hearing deficit (PTS) of more than 30 dB in frequencies larger 3 kHz. These 10 musicians played violins, contrabasses,

In this part of the study participated 20 industrial workers from a brewery who worked on bottle washing or bottle filling machines. Their hearing loss (PTS) of more than 20 dB SPL in the frequency range from 3.000 Hz to 8.000 Hz was officially recognized as an occupational disease. The workers were aged 38 to 63 years and had never had formal musical training or

The study was approved by the local ethics committee of the University of Jena. All participants gave informed consent to this study and received monetary compensation for their participa‐ tion. In a questionnaire, the participants were asked for their age; musical experiences, i.e., duration of employment in the orchestra or attending music school, instruments that are or were played, duration of training time per week, and the use of hearing protectors; occurrence of tinnitus; occurrence of ear, nose, and throat diseases; and hereditary ear diseases in the family. We also asked for noisy leisure time activities. The workers were asked similar questions with special respect for noise exposition per working shift. The hearing ability of the right and left ears in each participant was tested by means of a high frequency audiometer (Grahnert Präcitronic MA 22; Dresden, Germany, combined with a headphone HDA-200; Sennheiser, Hannover, Germany) and by measuring the otoacoustic emissions (DPOAE/

played any kind of music. All experiments were performed without hearing aids.

TEOAE) (Madsen, Denmark). Details were given by our group in the literature [12].

To study the perception of auditory stimuli, we recorded MMN using the classical ac-EEG technique. Participants were seated comfortably with closed eyes. They listened to the stimuli that were presented via loudspeakers in the free field mode and were instructed only to listen relaxed and to avoid attention or any reaction to the stimuli to minimize artifacts caused by

The ac-EEG was recorded from 32 electrodes (Figure 1) positioned according to the interna‐ tional 10/20 system over frontal, central, temporal and parietal brain areas of both hemispheres using the standardized Easy-Cap device (Easy Cap GmbH, Herrsching-Breitbrunn, Germany). A linked-mastoid electrode served as a reference. Impedance was maintained below 5 kOhm. An electrode at the forehead was used as a ground. The electrooculogram was recorded for rejection of artifacts (two electrodes above and below the eye, one electrode lateral to the eye).

**Normal hearing and hearing-impaired professional musicians, aged 28 to 68 years**

20 dB SPL in the frequency range from 3.000 Hz to 8.000 Hz.

**Hearing-impaired industrial workers, aged 38 to 63 years**

bassoon, cello, trombones, and oboe.

**2.2. Study design**

134 Update On Hearing Loss

movements.

Stimuli were pure C1-major chords, C3 chords, and respective mistuned chords in a classical oddball paradigm. The mistuned chords were generated by a synthesizer (variation +50 cent of the middle tone for the C-major chord, and variation +12 cent for the C3 chord) (Figure 2). A frequency and spectrogram analysis was performed to assure that the mistuned chords were in the same frequency range and had a similar intensity (integrating-averaging Sound Level Meter, type 118, class 1; Norsonic, Lierskog, Norway). Whereas the +50 cent variation was easy to differentiate from correct tunes, the +12 cent variation was difficult to discern for all nontrained listeners.

Stimuli were stored on a PC and presented in a free-field mode via the Presentation software (Presentation V9.12, NBS, Berkeley, CA) via two active loudspeakers as shown in Figure 3.

A recording session consisted of four trains per 200 single stimuli each. The participants listened with closed eyes to two trains of C1-major chords and to two trains of C3 chords. Parent and deviant stimuli were presented randomly in a 4:1 order and at randomized interstimulus intervals lasting from 2 to 6 seconds. We defined three different paradigms of stimulus occurrence: paradigm 1 had 150 normal and 50 mistuned C1-major chords, paradigm

**Figure 2.** Design of the musical chords produced with a computer synthesizer. The C1 major (ca. 400 Hz) were the low frequency stimuli and the C3 major (ca. 1300 Hz) the high frequency stimuli. For mistuning, the middle tone E was modified (marked with red in the lower panels on the left side). The diagram on the right shows a screenshot with the intensities of both stimuli in a frequency spectrum. Note that there is no significant difference in intensity between the normal and mistuned stimuli.

**Figure 3.** Schematic diagram of sound presentation and data recording setup in this study.

2 150 mistuned and 50 normal C1-major chords, and paradigm 3 150 normal and 50 mistuned C3-major chords. Non-musicians and professional musicians listened to all three paradigms. The stimulus intensity was set at 65 dB SPL.

The industrial workers listened only to musical stimuli in the paradigms 1 and 2 with the same number of stimuli. For testing the industrial workers with specific sounds they were trained to listen to we recorded samples of the machine noise as parent stimuli and interrupted this machine noise with short high-pitched whistles or with very short intervals of random white noise (deviant stimulus). Both types of stimuli were presented in an oddball paradigm with similar time intervals at an intensity of 65 dB SPL.

#### **2.4. Data analysis**

2 150 mistuned and 50 normal C1-major chords, and paradigm 3 150 normal and 50 mistuned C3-major chords. Non-musicians and professional musicians listened to all three paradigms.

**Figure 3.** Schematic diagram of sound presentation and data recording setup in this study.

**Figure 2.** Design of the musical chords produced with a computer synthesizer. The C1 major (ca. 400 Hz) were the low frequency stimuli and the C3 major (ca. 1300 Hz) the high frequency stimuli. For mistuning, the middle tone E was modified (marked with red in the lower panels on the left side). The diagram on the right shows a screenshot with the intensities of both stimuli in a frequency spectrum. Note that there is no significant difference in intensity between the

The stimulus intensity was set at 65 dB SPL.

normal and mistuned stimuli.

136 Update On Hearing Loss

Trials contaminated with artifacts (e.g., contractions of mimic muscles or eye movements) were excluded from further analysis. The AEP in the EEG were evaluated using the BrainVision Analyzer 2 (Brain Products, Munich, Germany). We observed a 512 ms time range with a 50 ms pre-stimulus interval. A set of raw EEG data from all electrodes is presented in Figure 4.

**Figure 4.** Specimen of an EEG recording, the recordings of EOG and of electrocardiogram with presentation of an audi‐ tory stimulus marked by the red dot and red line. The thin green lines indicate time intervals of 1 second. Note the desynchronization in the EEG beginning from the arrow for the next 1-2 seconds together with a longer lasting de‐ crease in momentarily heart frequency.

According to widely accepted procedures [20-22], we analyzed the maximal amplitudes and latencies of the first negative component (N1), of the second positive component (P2), and we analyzed the area under the curve for the second negative component (N2) in the time range from 250-340 ms. The latter was done since not in all cases we could discern a typical or even a single peak for the component of the AEP. The MMN was measured as the difference curve between the AEP to deviant and parent chords in that time interval (Figure 5). Amplitudes and latencies were compared between parent and deviant stimuli by t-tests (student) and between the groups by one-way ANOVA as well. Separate tests were performed to determine whether the MMN-amplitudes differed for non-musicians and professional musicians as well as for normal hearing musicians and hearing-impaired musicians.

**Figure 5.** Specimen of a mean auditory evoked potential with labeling of the N1 and P2 components (amplitudes and latencies accentuated with dotted lines). The time interval in which we looked for the MMN is marked in grey, and the MMN is marked in green. The blue curve depicts the mean value to the frequently presented (parent) stimuli, the red one to the infrequently presented (deviant) stimuli.

To assess whether listening to mistuned chords had influence on momentary EEG-activity, we performed a Fast Fourier-Transformation (FFT) with the BrainVision Analyzer 2 in the interstimulus interval to see whether EEG-activity shifted to higher frequencies after mistuned chords. In addition, we analyzed the changes in mean heart rate (average of the heart rate during listening to in-tune music vs. mistuned tones) within the same time interval. A statistical comparison was made by means of the Wilcoxon matched pairs signed-ranks test. Statistical significance was set at 5%. Though we performed the analysis for all EEG electrodes, for better clarity we present here only data from the Cz electrodes.

#### **3. Results**

#### **3.1. Amplitudes and latencies of N1 and P2 components of the AEP in normal hearing probands**

As can be seen in Figure 6, our presented chords evoked stable and replicable AEP both in non-musicians and in professional musicians that differed only slightly between both groups. In both groups the presentation of mistuned chords induced larger P2 components than the presentation of normal chords.

According to widely accepted procedures [20-22], we analyzed the maximal amplitudes and latencies of the first negative component (N1), of the second positive component (P2), and we analyzed the area under the curve for the second negative component (N2) in the time range from 250-340 ms. The latter was done since not in all cases we could discern a typical or even a single peak for the component of the AEP. The MMN was measured as the difference curve between the AEP to deviant and parent chords in that time interval (Figure 5). Amplitudes and latencies were compared between parent and deviant stimuli by t-tests (student) and between the groups by one-way ANOVA as well. Separate tests were performed to determine whether the MMN-amplitudes differed for non-musicians and professional musicians as well

**Figure 5.** Specimen of a mean auditory evoked potential with labeling of the N1 and P2 components (amplitudes and latencies accentuated with dotted lines). The time interval in which we looked for the MMN is marked in grey, and the MMN is marked in green. The blue curve depicts the mean value to the frequently presented (parent) stimuli, the red

To assess whether listening to mistuned chords had influence on momentary EEG-activity, we performed a Fast Fourier-Transformation (FFT) with the BrainVision Analyzer 2 in the interstimulus interval to see whether EEG-activity shifted to higher frequencies after mistuned chords. In addition, we analyzed the changes in mean heart rate (average of the heart rate during listening to in-tune music vs. mistuned tones) within the same time interval. A statistical comparison was made by means of the Wilcoxon matched pairs signed-ranks test. Statistical significance was set at 5%. Though we performed the analysis for all EEG electrodes,

**3.1. Amplitudes and latencies of N1 and P2 components of the AEP in normal hearing**

As can be seen in Figure 6, our presented chords evoked stable and replicable AEP both in non-musicians and in professional musicians that differed only slightly between both groups.

as for normal hearing musicians and hearing-impaired musicians.

for better clarity we present here only data from the Cz electrodes.

one to the infrequently presented (deviant) stimuli.

**3. Results**

138 Update On Hearing Loss

**probands**

**Figure 6.** Mean values of AEP evoked by normal or mistuned stimuli in musicians (left diagrams) and in non-musi‐ cians (right diagrams). The bluish areas mark the time range in which we analyzed the differences between the AEP. The difference curves are shown in black. The blue lines represent AEP to frequently presented chords, the red lines AEP to the infrequently presented ones. For a better visibility the standard deviations of the curves are omitted. A and B show that normal chords occurred frequently (paradigm 1). C and D show that mistuned chords occurred frequently (paradigm 2). Note the small differences between normal tuned and mistuned chords in non-musicians in diagrams B and D.

The peak of the N1 component was seen at about 128 ms after the stimulus, the peak of the P2 component at about 224 ms after the stimulus. Mean N1 amplitudes amounted to about 7 μV, mean P2 amplitudes to 5 μV. A detailed comparison between the groups of musicians and non-musicians and the three paradigms is given in Figure 7. It should be noted that both C3 major chords resulted in markedly larger areas under the curve both for the N1 and for the P2 components in non-musicians and in musicians. However, the area under the curve of the P2 component was larger when C3-major chords were presented than when C1-major chords were presented.

**Figure 7.** AEP components from normal hearing non-musicians and musicians. The bars give the mean values ± std. dev. The asterisks mark statistically significant differences (p<0.05). A) Latency times of the N1 component. B) Ampli‐ tudes of the P2 component. C) Areas under the curves of the N1 component. D) Areas under the curve of the P2 com‐ ponent.

Interestingly, the EEG activity differed markedly between both groups when the late compo‐ nents of the AEP were compared that were recorded from the Cz electrode and an activity map was computed by the brain vision software. Though the general pattern was alike, a general higher activity rate was seen in musicians over the temporo-occipital cortex and a lower activity in the vertex area of the brain (Figure 8).

#### **3.2. Amplitudes and latencies of N1 and P2 components of the AEP in hearing-impaired probands**

All professional musicians in this group had a hearing loss in the mid- and/or high-frequency range with a mean PTS up to 35 dB SPL. No significant differences were obtained when left and right ears were tested so a preferential side of hearing loss could be excluded. All hearingimpaired industrial workers suffered from hearing loss that was recognized as an occupational disease. The hearing deficit had a similar magnitude as in the hearing-impaired professional musicians and was also found at both ears with a slight but insignificant preference to the left ears (Figure 9).

Hearing Impairment in Professional Musicians and Industrial Workers — Profession-Specific Auditory Stimuli... http://dx.doi.org/10.5772/61137 141

**Figure 8.** Comparison of cortical EEG activity after stimulation with normal C1-major chords. The AEP curves show the grand mean value from all participants and the activity maps the distribution of cortical activity at different mo‐ ments after the stimulus in the time range marked in blue. A) Data from normal hearing non-musicians. B) Data from normal hearing musicians.

**Figure 9.** Mean values ± std. dev. of hearing loss in the left and right ears of the 10 hearing-impaired professional musi‐ cians (left) and of the 20 hearing-impaired industrial workers (right).

**Figure 7.** AEP components from normal hearing non-musicians and musicians. The bars give the mean values ± std. dev. The asterisks mark statistically significant differences (p<0.05). A) Latency times of the N1 component. B) Ampli‐ tudes of the P2 component. C) Areas under the curves of the N1 component. D) Areas under the curve of the P2 com‐

Interestingly, the EEG activity differed markedly between both groups when the late compo‐ nents of the AEP were compared that were recorded from the Cz electrode and an activity map was computed by the brain vision software. Though the general pattern was alike, a general higher activity rate was seen in musicians over the temporo-occipital cortex and a lower

**3.2. Amplitudes and latencies of N1 and P2 components of the AEP in hearing-impaired**

All professional musicians in this group had a hearing loss in the mid- and/or high-frequency range with a mean PTS up to 35 dB SPL. No significant differences were obtained when left and right ears were tested so a preferential side of hearing loss could be excluded. All hearingimpaired industrial workers suffered from hearing loss that was recognized as an occupational disease. The hearing deficit had a similar magnitude as in the hearing-impaired professional musicians and was also found at both ears with a slight but insignificant preference to the left

activity in the vertex area of the brain (Figure 8).

ponent.

140 Update On Hearing Loss

**probands**

ears (Figure 9).

When tested with the auditory stimuli, the parameters of the AEP components differed from the data obtained in normal hearing musicians. The N1 peaks were found earlier (C1 chord 121 ms, C3 chord 109 ms after stimulus) and had larger amplitudes (C1 chord 11 μV, C3 chord 11 μV). The same was seen for the P2 peaks (latency for C1 chords 213 ms, for C3 chords 202 ms; amplitude for C1 chords 5 μV, for C3 chords 8 μV). The latter difference was even significant between C1 chords and C3 chords in this group.

For both stimulus types (normal or mistuned), neither amplitudes nor latencies of the N1 component showed significant differences between non-musicians, normal hearing or hearing-impaired musicians. Responses to parent or deviant stimuli did not differ, regardless whether in-tune or mistuned chords were given as parent stimuli. Similarly, no significant difference existed when comparing the N1 components to the mid-frequency (C1; paradigm 1) or to high-frequency (C3; paradigm 3) stimulation when the chords were mistuned by either 50 cent or by 12 cent.

The workers were first presented the same auditory stimuli as the other participants in this study, i.e., C1-major chords. When analyzing the AEP, we found later N1 amplitudes (peak 134 ms after stimulus) when the paradigm 1 was used, and same latencies as in non-musicians, when the paradigm 2 was used (N1 peak 128 ms after stimulus). The N1 amplitudes ranged from 10 to 12 μV and differed only slightly from those we obtained in non-musicians (Figure 10A and 10B). A similar result was seen when we analyzed the P2 components of the AEP. In this group, the latencies ranged from 228 to 237 ms after stimulus in paradigm 1 and from 218 to 226 ms in paradigm 2 that was later than in musicians, but in the same range as in nonmusicians. The P2 amplitudes ranged from 7 to 11 μV and did not differ significantly to the other participants. Both musicians and industrial workers had larger P2 areas under the curve either when the mistuned stimuli were presented rarely in the paradigms 1 (Figure 10C) or often in the paradigms 2 (Figure 10D).

**Figure 10.** Comparison of amplitudes of the N1 components and of the areas under the curve for the P2 components of the AEP in hearing-impaired musicians and in hearing-impaired industrial workers. Data are presented as mean val‐ ues ± std. dev. The asterisk marks statistically significant differences (p<0.05). A) N1 latencies in paradigm 1. B) N1 latencies in paradigm 2. C) P2 areas under the curve in paradigm 1. D) P2 areas under the curve in paradigm 2.

In a second part of the study, the workers had to listen to machine noise that was either unchanged (parent stimulus) or interrupted/disturbed by short high-pitched whistles. This type of stimulation did not evoke typical AEP, but was used to look for activity changes in the EEG (see below).

#### **3.3. Comparison of the MMN**

134 ms after stimulus) when the paradigm 1 was used, and same latencies as in non-musicians, when the paradigm 2 was used (N1 peak 128 ms after stimulus). The N1 amplitudes ranged from 10 to 12 μV and differed only slightly from those we obtained in non-musicians (Figure 10A and 10B). A similar result was seen when we analyzed the P2 components of the AEP. In this group, the latencies ranged from 228 to 237 ms after stimulus in paradigm 1 and from 218 to 226 ms in paradigm 2 that was later than in musicians, but in the same range as in nonmusicians. The P2 amplitudes ranged from 7 to 11 μV and did not differ significantly to the other participants. Both musicians and industrial workers had larger P2 areas under the curve either when the mistuned stimuli were presented rarely in the paradigms 1 (Figure 10C) or

**Figure 10.** Comparison of amplitudes of the N1 components and of the areas under the curve for the P2 components of the AEP in hearing-impaired musicians and in hearing-impaired industrial workers. Data are presented as mean val‐ ues ± std. dev. The asterisk marks statistically significant differences (p<0.05). A) N1 latencies in paradigm 1. B) N1 latencies in paradigm 2. C) P2 areas under the curve in paradigm 1. D) P2 areas under the curve in paradigm 2.

In a second part of the study, the workers had to listen to machine noise that was either unchanged (parent stimulus) or interrupted/disturbed by short high-pitched whistles. This type of stimulation did not evoke typical AEP, but was used to look for activity changes in the

often in the paradigms 2 (Figure 10D).

142 Update On Hearing Loss

EEG (see below).

When interviewed after the series both normal hearing and hearing-impaired musicians complained about the mistuned chords. They told us that they were annoyed at the mistuned chords, but hearing-impaired non-musicians and hearing-impaired industrial workers had not perceived the small differences between the stimuli.

Hearing-impaired musicians were still able to distinguish between in-tune and mistuned chords in both the C1 and in the C3 chords regardless of the degree of mistuning. Their areas under the curve for the MMN were significantly larger when the C1 chords were presented and mistuned stimuli occurred rarely (paradigm 1), which is shown in Figure 11.

**Figure 11.** Comparison of areas under the curve for the stimulation with C1 chords in paradigm 1 (black bar) and in paradigm 2 (red bar). Data are presented as mean values ± std. dev. The asterisk marks a significant difference (p<0.05).

Independent from hearing impairment, rarely occurring chords (either normal or mistuned) in the musicians group evoked larger areas under the curve for the P2 components (Figure 12).

Interestingly, in hearing-impaired industrial workers, a similar but statistically insignificant difference was seen between the areas under the curve for the P2 component, though the workers told in the interview that they did not observe any differences between the presented chords. This difference was seen both when the mistuned stimulus was presented rarely or often (Figure 13).

The investigation of the MMN curves (AEP to deviant minus AEP to standard stimuli) confirmed differences between non-musicians and both groups of musicians. In normal hearing musicians, the MMN was found in the time range from 180-250 ms after stimulus and a similar, but even longer lasting MMN (up to 300 ms after stimulus), was seen in hearingimpaired musicians. The MMN curves after high-frequency stimulation (C3 chords), however, allowed a clear differentiation between professional musicians and non-musicians. Non-

**Figure 12.** Comparison of the areas under the curve for the P2 components of the AEP in hearing-impaired professio‐ nal musicians. Data are presented as mean values ± std. dev. The asterisks mark significant differences (p<0.05). Black bars show responses to the parent stimuli, the brown bars show the responses to the deviant stimuli. A) C1 chord, paradigm 1. B) C1chord, paradigm 2. C) C3 chord, paradigm 3.

**Figure 13.** Areas under the curve for the P2 component recorded in hearing-impaired workers. Data are presented as mean values ± std. dev. The red bars show responses to parent stimuli, the green ones to deviant stimuli. A) Presenta‐ tion in paradigm 1 (mistuned stimuli occur rarely). B) Presentation in paradigm 2 (normal stimuli occur rarely).

musicians had no typical MMN in the observed time range. In normal hearing musicians, this MMN occurred in the range of 250-340 ms after stimulus and a small, but clearly discernable MMN was also found in hearing-impaired musicians. In the latter group, however, the MMN started earlier (220-230 ms after stimulus).

#### **3.4. FFT analysis of the EEG and heart rate analysis**

Due to the instructions to the participants (closed eyes, relaxed sitting position, no directed attention to the stimuli), highest spectral power was found in the alpha band, thus confirming that the participants followed the instructions. In both groups of musicians, we found a shift in power density towards higher alpha EEG activity in the interstimulus intervals after presentation of mistuned chords. Such a large shift failed to occur in non-musicians, when the same stimuli were presented. In this group EEG power spectra density was the same, regard‐ less whether in-tune or mistuned chords were presented (Figure 14).

**Figure 14.** FFT-analysis of the EEG shown as diagrams of regional spectral EEG power and as frequency split maps for musicians (top) and non-musicians (bottom). The light blue bar in the power spectra marks the frequency range that is further analyzed in the frequency split maps. Note the activity shifts towards higher alpha frequencies in musicians when mistuned stimuli were presented. Such a shift failed to occur in non-musicians.

In the same groups we analyzed the heart rates and found a significant increase in mean heart rate in musicians after listening to mistuned chords compared to the resting situation, but no significant differences when comparing resting situation vs. hearing of in-tune chords (resting situation 69.6±12.4 beats per minute, 70.2±12.4 beats per minute after in-tune chords, 71.4±11.5

musicians had no typical MMN in the observed time range. In normal hearing musicians, this MMN occurred in the range of 250-340 ms after stimulus and a small, but clearly discernable MMN was also found in hearing-impaired musicians. In the latter group, however, the MMN

**Figure 13.** Areas under the curve for the P2 component recorded in hearing-impaired workers. Data are presented as mean values ± std. dev. The red bars show responses to parent stimuli, the green ones to deviant stimuli. A) Presenta‐ tion in paradigm 1 (mistuned stimuli occur rarely). B) Presentation in paradigm 2 (normal stimuli occur rarely).

**Figure 12.** Comparison of the areas under the curve for the P2 components of the AEP in hearing-impaired professio‐ nal musicians. Data are presented as mean values ± std. dev. The asterisks mark significant differences (p<0.05). Black bars show responses to the parent stimuli, the brown bars show the responses to the deviant stimuli. A) C1 chord,

started earlier (220-230 ms after stimulus).

paradigm 1. B) C1chord, paradigm 2. C) C3 chord, paradigm 3.

144 Update On Hearing Loss

beats per minute after mistuned chords; n=15; Wilcoxon matched pairs signed-ranks test, p=0.0353). The mean heart frequency, however, did not change in non-musicians (resting situation 60,7±8.1 beats per minute, 60.5±7.5 beats per minute after in-tune chords, 60.8±8.7 beats per minute after mistuned chords; n=10).

Hearing-impaired industrial workers always negated to have noticed the mistuned stimuli, though we had recorded typical MMN to the rare stimulus. In order to present a professionspecific sound to this group, we had used short sequences of the unchanged machine noise and the same noise with high-pitched whistles that sounded like very short pips.

As expected from the pre-trial interviews where the hearing-impaired workers claimed that they easily could discern even one broken bottle in the machine sound, the workers con‐ firmed after the trials that they had heard the rarely occurring disturbed noise samples. In the EEG, the occurrence of these rare stimuli caused a desynchronization lasting for 5-6 seconds (Figure 15).

**Figure 15.** Sample EEG recording from one hearing-impaired industrial worker. The black dot at the bottom marks the presentation of the disturbed machine noise; the onset of the desynchronization in the EEG is marked by an arrow.

beats per minute after mistuned chords; n=15; Wilcoxon matched pairs signed-ranks test, p=0.0353). The mean heart frequency, however, did not change in non-musicians (resting situation 60,7±8.1 beats per minute, 60.5±7.5 beats per minute after in-tune chords, 60.8±8.7

Hearing-impaired industrial workers always negated to have noticed the mistuned stimuli, though we had recorded typical MMN to the rare stimulus. In order to present a professionspecific sound to this group, we had used short sequences of the unchanged machine noise

As expected from the pre-trial interviews where the hearing-impaired workers claimed that they easily could discern even one broken bottle in the machine sound, the workers con‐ firmed after the trials that they had heard the rarely occurring disturbed noise samples. In the EEG, the occurrence of these rare stimuli caused a desynchronization lasting for 5-6 seconds

**Figure 15.** Sample EEG recording from one hearing-impaired industrial worker. The black dot at the bottom marks the presentation of the disturbed machine noise; the onset of the desynchronization in the EEG is marked by an arrow.

and the same noise with high-pitched whistles that sounded like very short pips.

beats per minute after mistuned chords; n=10).

(Figure 15).

146 Update On Hearing Loss

**Figure 16.** FFT-analysis of the EEG shown as diagrams of regional spectral EEG power and as frequency split maps for normal undisturbed machine noise was presented (left panel), and when the machine noise was disturbed by short pips (right panel). The light blue bar in the power spectra marks the frequency range that is further analyzed in the frequency split maps.

We performed the same FFT-analysis of the EEG in the workers and revealed a shift in the frequency towards higher alpha bands when the disturbed noise was presented (Figure 16). During undisturbed noise the EEG activity had its maximum at 9.7 Hz and was preferentially distributed in the right hemisphere, and only a small area of this hemisphere showed a 10.0 Hz EEG. When we presented the disturbed noise, in a larger area of the brain at both hemi‐ spheres a 10.0 Hz EEG and in the frontal parts of the cortex even a 10.7 Hz EEG were observed. The mean EEG frequency increased from 9.2±0.6 Hz during undisturbed noise to 9.4±0.6 Hz during disturbed noise.

**Figure 17.** Mean values of EEG power spectra ± std. dev. in hearing-impaired industrial workers when typical machine noise was presented. The red bar shows the data during undisturbed noise; the green one shows the data during dis‐ turbed noise.

In addition, we analyzed the power spectra in the frequency range from 12 to 14 Hz at the Cz electrode and found significantly higher regional EEG spectral power in hearing-impaired industrial workers when disturbed machine noise was presented (Figure 17).

#### **4. Discussion**

For the first time in this study, profession-specific stimuli were used to assess the effects of hearing deficits in professional musicians and in industrial workers. Here we have shown that parameters of AEP and MMN to mistuned chords differ between musicians and non-musi‐ cians, as well as between normal hearing and hearing-impaired musicians, and that compo‐ nents of the AEP and the MMN can be used to differentiate between the three investigated groups. FFT analysis of the EEG in the interstimulus intervals confirmed that mistuned chords caused a state of higher EEG activity only in musicians, regardless of their hearing loss. Another evidence was the occurrence of heart rate changes only in musicians. Therefore we conclude that both perception and processing of musical signals differ between musicians and non-musicians. In hearing-impaired workers, the disturbed machine noise caused a state of higher EEG activity as well.

It is known that complex stimuli such as complex derived words can produce MMN [23]. The stimuli we used were chosen from the typical occupational environment of the professional musician, i.e., musical chords. Complex musical sounds are used to produce MMN, e.g., to compare timbre processing in harmonically rich sounds versus single sinusoidal tones [24]. We had expected that musicians with ongoing musical training over several years have learned to hear and to evaluate these stimuli with their professional memory. Marked differences between tuned and mistuned chords should be recognized easily by musicians, but also by non-musicians. Smaller differences, however, when stimuli were presented in the highfrequency range should be recognized only by musicians. To our knowledge, such a study had not been done before in hearing-impaired musicians.

Intense musical training resulted in an increase in area of primary and secondary audito‐ ry cortices [25-27]. In line with this finding, fMRI investigations in musicians revealed a coactivation of both auditory and sensomotor areas in the cortex, thus showing that musical training changes the connectivity and probably also the processing strategies in the brain of musicians [28-30]. Long-term musical training enhances the short-term memory for auditory stimuli and eased behavioral tasks, e.g., detection of deviant tones in a series of auditory stimuli [31].

Our results confirmed the efficacy of comparison of event-related potentials to differentiate between trained musicians and non-musicians [32,33]. The effect of training to induce neural plasticity in the auditory system has been shown in musical conductors compared to nonmusicians in a spatial detection task [34], in a pitch detection task [35] or in MMN evoked by variations of complex tone patterns, where long-term musical training modulated the encod‐ ing of wrong tones in the right hemisphere of musicians [36]. This is an ongoing process starting in pre-adolescence, since musically trained children had larger MMN to slightly mistuned tones compared to age-matched, non-trained children already at the age of 11, thus confirming that musical training indeed could be responsible for the larger negativity [37]. The cortical plasticity can even be improved, if not only auditory but also somatosensory tasks should be solved, e.g., learning to judge whether music was correctly played versus learning to play an instrument [38]. Interestingly, in hearing-impaired musicians we found clearly distinguishable MMNs, as well as changes in EEG power spectra after presentation of mistuned chords. Even when the stimulus was in the frequency range that was affected by the hearing disability (C3 paradigm), the professional musicians were able to differentiate between in-tune and mistuned chords. However, the normal hearing untrained non-musicians were only able to differentiate to heavily mistuned (50 cent) stimuli, but the hearing impaired did not. The results of inter‐ views confirmed that the mistuned stimuli were recognized both by normal hearing and by hearing-impaired musicians and caused a state of unhappiness.

In addition, we analyzed the power spectra in the frequency range from 12 to 14 Hz at the Cz electrode and found significantly higher regional EEG spectral power in hearing-impaired

For the first time in this study, profession-specific stimuli were used to assess the effects of hearing deficits in professional musicians and in industrial workers. Here we have shown that parameters of AEP and MMN to mistuned chords differ between musicians and non-musi‐ cians, as well as between normal hearing and hearing-impaired musicians, and that compo‐ nents of the AEP and the MMN can be used to differentiate between the three investigated groups. FFT analysis of the EEG in the interstimulus intervals confirmed that mistuned chords caused a state of higher EEG activity only in musicians, regardless of their hearing loss. Another evidence was the occurrence of heart rate changes only in musicians. Therefore we conclude that both perception and processing of musical signals differ between musicians and non-musicians. In hearing-impaired workers, the disturbed machine noise caused a state of

It is known that complex stimuli such as complex derived words can produce MMN [23]. The stimuli we used were chosen from the typical occupational environment of the professional musician, i.e., musical chords. Complex musical sounds are used to produce MMN, e.g., to compare timbre processing in harmonically rich sounds versus single sinusoidal tones [24]. We had expected that musicians with ongoing musical training over several years have learned to hear and to evaluate these stimuli with their professional memory. Marked differences between tuned and mistuned chords should be recognized easily by musicians, but also by non-musicians. Smaller differences, however, when stimuli were presented in the highfrequency range should be recognized only by musicians. To our knowledge, such a study had

Intense musical training resulted in an increase in area of primary and secondary audito‐ ry cortices [25-27]. In line with this finding, fMRI investigations in musicians revealed a coactivation of both auditory and sensomotor areas in the cortex, thus showing that musical training changes the connectivity and probably also the processing strategies in the brain of musicians [28-30]. Long-term musical training enhances the short-term memory for auditory stimuli and eased behavioral tasks, e.g., detection of deviant tones in a series of

Our results confirmed the efficacy of comparison of event-related potentials to differentiate between trained musicians and non-musicians [32,33]. The effect of training to induce neural plasticity in the auditory system has been shown in musical conductors compared to nonmusicians in a spatial detection task [34], in a pitch detection task [35] or in MMN evoked by variations of complex tone patterns, where long-term musical training modulated the encod‐ ing of wrong tones in the right hemisphere of musicians [36]. This is an ongoing process starting in pre-adolescence, since musically trained children had larger MMN to slightly mistuned

industrial workers when disturbed machine noise was presented (Figure 17).

**4. Discussion**

148 Update On Hearing Loss

higher EEG activity as well.

auditory stimuli [31].

not been done before in hearing-impaired musicians.

We could prove this when we tested the hearing-impaired workers with chord stimuli. The workers had similar hearing deficits in a similar frequency range as the hearing professional musicians. The musicians easily recognized the mistuned stimuli and commented on their occurrence in the interviews after the trials, but the workers who never before had heard those stimuli did not. The early AEP components (N1 amplitudes and latencies) did not indicate different processing of the mistuned chords by the workers. The late AEP components (P2 area under the curve and MMN), however, indicated that the mistuned stimuli were sensed and processed differently, even if the person was not aware of this stimulus [39]. Unfortunately, we could not test this phenomenon reversely with the professional musicians, since they refused stimulation with machine noise. We suppose that such unfamiliar stimuli would be difficult to discern by the musicians.

To explain the ability of hearing-impaired musicians to differentiate between "right" and "wrong" tunes several considerations are necessary. We can exclude a significantly varied loudness of the tuned versus the mistuned stimuli. In the group of hearing-impaired musi‐ cians, audiological investigations provided evidence for a diminished peripheral input. This impairment might explain the delayed and smaller amplitude of the P2 component as well as the smaller areas under the curve for the N2 component and the smaller resulting MMNs than in normal hearing musicians. Interestingly, the AEP had a similar amplitude and time shape both after stimulation with the high-frequent C3 paradigm and with the mid-frequent C1 major chords, thus confirming that the hearing damage should have affected a larger part of the cochlea. In agreement with a previous study [8], we had instructed the participants to sit relaxed and not to pay attention to the chords. Therefore, we conclude that we were able to record a non-attentional, automatic processing of musical signals. Musicians that were trained to those signals should process this information more effectively [8]. In line with this, musicians were less dependent on the salience of an acoustical environment, but in non-musicians salience had a stronger impact on the processing of complex tone patterns [36]. Assuming that musical training had already caused this effect before hearing impairment started, it is likely that the diminished input could be processed in professional musicians with still higher efficacy than in untrained non-musicians. Another statement in the literature [10] gives support to our interpretation: musical training should result in a more accurate tuning of the frequency-specific neurons in musicians compared to non-musicians. There is indication for a better top-down modulation of auditory processing in trained musicians for both musical sounds and speech [40]. We suppose, therefore, that a better tuning function of the neurons would result in more accurate processing of the rest of a signal when the input is diminished by cochlear damage. In line with this, we found in hearing-impaired musicians significant earlier N1 and P2 components than in hearing-impaired industrial workers when musicianspecific chords were used as stimuli.

We conclude that our observed smaller MMNs to mistuned chords in hearing-impaired professional musicians reflect central compensation mechanisms that are able to improve the processing of profession-specific signals, i.e., musical chords. This compensation does not take place in situations of normal life (i.e., without ongoing formal training), e.g., watching TV, using a headphone or cellular phone, or in situations with a loud background that disturbs the incoming signals. In these situations, hearing-impaired musicians complain about the hearing deficit though they are able to play their instruments correctly.

The musicians investigated in our study were interested in learning about hearing damage and the proper use of hearing protectors. Nevertheless, the acceptance of hearing protectors (custom-built ear plugs for specific instruments) among musicians in classical orchestras is very small; more than 90% dislike such devices. Another number has been observed among rock musicians - there is a rate of nearly 50% who accept such hearing protectors [41,42]. Hearing loss among professional musicians in Germany has so far not been accepted as an occupational disease though sound intensities exceed the limits allowed for a working shift in many orchestras [12,43]. The lack of rules to prevent hearing loss in professional classical musicians and the ongoing dispute whether sound exposure during rehearsals or performan‐ ces is high enough to induce hearing loss hinders the discussion to foster the use of hearing protection in that profession [44-48].

In conclusion, our data indicate that a differentiation between non-musicians and musicians is possible by analyzing AEP components or the MMN when profession-specific stimuli are used. The MMN was still present in hearing-impaired professional musicians, although they had a hearing deficit in the frequency range of the musical stimuli. Probably, the intense musical training has enhanced the processing structures and/or efficacy to evaluate the musical stimulus. A similar result was seen in the workers: ongoing professional training enabled the detection of disturbed machine noise though this group was unable to detect differences in non-trained musical sounds.

To answer the hypotheses postulated at the beginning:

**1.** Musical chords are a suitable stimulus to evoke stable and replicable AEP both in musicians and in people who are not trained to musical stimuli. AEP evoked by those stimuli can be used to differentiate between trained and untrained persons. Especially the late components of the AEP differ and depend on the learned stimulus. Ongoing profes‐ sional training to specific sounds is a learning process that is reflected in different sound processing and in the late components of the AEP.


### **Nomenclature and Abbreviations**

frequency-specific neurons in musicians compared to non-musicians. There is indication for a better top-down modulation of auditory processing in trained musicians for both musical sounds and speech [40]. We suppose, therefore, that a better tuning function of the neurons would result in more accurate processing of the rest of a signal when the input is diminished by cochlear damage. In line with this, we found in hearing-impaired musicians significant earlier N1 and P2 components than in hearing-impaired industrial workers when musician-

We conclude that our observed smaller MMNs to mistuned chords in hearing-impaired professional musicians reflect central compensation mechanisms that are able to improve the processing of profession-specific signals, i.e., musical chords. This compensation does not take place in situations of normal life (i.e., without ongoing formal training), e.g., watching TV, using a headphone or cellular phone, or in situations with a loud background that disturbs the incoming signals. In these situations, hearing-impaired musicians complain about the hearing

The musicians investigated in our study were interested in learning about hearing damage and the proper use of hearing protectors. Nevertheless, the acceptance of hearing protectors (custom-built ear plugs for specific instruments) among musicians in classical orchestras is very small; more than 90% dislike such devices. Another number has been observed among rock musicians - there is a rate of nearly 50% who accept such hearing protectors [41,42]. Hearing loss among professional musicians in Germany has so far not been accepted as an occupational disease though sound intensities exceed the limits allowed for a working shift in many orchestras [12,43]. The lack of rules to prevent hearing loss in professional classical musicians and the ongoing dispute whether sound exposure during rehearsals or performan‐ ces is high enough to induce hearing loss hinders the discussion to foster the use of hearing

In conclusion, our data indicate that a differentiation between non-musicians and musicians is possible by analyzing AEP components or the MMN when profession-specific stimuli are used. The MMN was still present in hearing-impaired professional musicians, although they had a hearing deficit in the frequency range of the musical stimuli. Probably, the intense musical training has enhanced the processing structures and/or efficacy to evaluate the musical stimulus. A similar result was seen in the workers: ongoing professional training enabled the detection of disturbed machine noise though this group was unable to detect differences in

**1.** Musical chords are a suitable stimulus to evoke stable and replicable AEP both in musicians and in people who are not trained to musical stimuli. AEP evoked by those stimuli can be used to differentiate between trained and untrained persons. Especially the late components of the AEP differ and depend on the learned stimulus. Ongoing profes‐ sional training to specific sounds is a learning process that is reflected in different sound

specific chords were used as stimuli.

150 Update On Hearing Loss

protection in that profession [44-48].

non-trained musical sounds.

To answer the hypotheses postulated at the beginning:

processing and in the late components of the AEP.

deficit though they are able to play their instruments correctly.

AEP; Auditory evoked potential ANOVA; Analysis of variance DPOAE; Distortion product otoacoustic emissions EEG; Electroencephalogram FFT; Fast Fourier transformation MMN; Mismatch Negativity PTS; Permanent threshold shift TEOAE; Transient-evoked otoacoustic emissions VEOG; Vertical electrooculogram

### **Acknowledgements**

The study has been supported by a grant of the Berufsgenossenschaft Nahrungsmittel und Gaststätten (Employer's Liability Insurance Association) and by the Kompetenzzentrum für Interdisziplinäre Prävention (KIP) of the Friedrich Schiller University Jena.

#### **Author details**

Edeltraut Emmerich, Marcus Engelmann, Melanie Rohmann and Frank Richter\*

Institute of Physiology I/Neurophysiology, University Hospital Jena - Friedrich Schiller University, Jena, Germany

### **References**


Bundesanstalt für Arbeitsschutz und Arbeitsmedizin - Fb 1041. Dortmund: Wirtschaftsverlag NW; 2005.

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[35] Münte TF, Nager W, Rosenthal O, Johannes S, Altenmüller E. Attention to pitch in musicians and non-musicians: An event-related brain potential study. In: Nakada T. (ed.) Integrated Human Brain Science. Amsterdam: Elsevier; 2000. p. 389-398. [36] Kuchenbuch A, Paraskevopoulos E, Herholz SC, Pantev C. Effects of musical training and event probabilities on encoding of complex tone patterns. BMC Neuroscience.

[37] Putkinen V, Tervaniemi M, Saarkivi K, de Vent N, Huotilainen M. Investigating the effects of musical training on functional brain development with a novel Melodic

[38] Pantev C, Lappe C, Herholz SC, Trainor L. Auditory-somatosensory integration and cortical plasticity in musical training. Annals of the New York Academy of Sciences.

[39] Engelmann M. Untersuchungen von Komponenten akustisch evozierter Potentiale an schwerhörigen Industriearbeitern. MD thesis. University Hospital Jena - Friedrich

[40] Tervaniemi M, Kruck S, De Baene W, Schroger E, Alter K.Friederici AD. Top-down modulation of auditory processing: Effects of sound context, musical expertise and

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## **Hearing Loss and Tinnitus**

## **A Combination of EGb 761 and Soft Laser Therapy in Chronic Tinnitus**

Klára Procházková, Ivan Šejna, Petr Schalek, Jozef Rosina and Aleš Hahn

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/61740

#### **Abstract**

**Objective**: We aimed to verify the therapeutic effect of soft laser in a combination with Ginkgo biloba extract EGb 761 in patients suffering from chronic tinnitus.

**Background data**: Tinnitus is described as an illusory sound perceived by the patient when there is no corresponding source of this sound outside. Tinnitus may signify a disturbance of peripheral or central part of hearing system. Beside the hearing system, there might be an utterly different etiology of tinnitus. Cardiovascular, musculoske‐ letal, mental, and other disorders can contribute to tinnitus formation as well. Due to these multiple etiologic factors the treatment is very difficult.

Studies analyzing biological effects of EGb 761 and laser suggest their use in tinnitus treatment. However, clinical study results are very variable, which makes their general use more controversial.

**Methods**: We conducted a simple prospective study including 420 patients suffering from chronic tinnitus (duration 3 months to 40 years; 7.7 years mean value; SD 7.8). A soft laser BTL-10 type was used with an 830 nm / 200 mV probe, at an energy density of 50 J/cm2 , applied with transmastoidal and transmeatal approach in a continuous and pulse beam, after 3 weeks of oral use of EGb 761. The therapeutic effect was evaluated by tinnitus intensity and frequency determination (tinnitus masking) and by the subjective rating on visual analogue scale (VAS) with 0 - 10 points.

**Results**: Among the 420 patients, 238 (56, 7%) achieved improvement in the tinnitus masking, the average improvement in terms of intensity was found to be 30dB. Hundred and ninety-six patients (46, 7%) recorded improvement on VAS. The objective and subjective evaluation coincided in 79% of cases.

© 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**Conclusion**: Compared to the outcomes of other studies, our findings reveal a relatively higher percentage of positive changes regarding the tinnitus status and greater congruence of objective (audiometric) and subjective (VAS) results.

**Keywords:** Tinnitus, EGb 761, laser

#### **1. Introduction**

Tinnitus is described as an illusory sound perceived by the patient when there is no corre‐ sponding source of this sound outside. Tinnitus is present in 5 - 15% of the population and in 70% of patients with hearing disturbances. Tinnitus may signify a disturbance of the peripheral or central part of the hearing system. Beside the hearing system, there are more possible causes of tinnitus - cardiovascular, musculoskeletal, metabolic, and endocrine dysfunctions (dyslipi‐ demia, thyroid dysfunction, diabetes mellitus), and stress and mental disorders might contribute to tinnitus formation as well. Despite the diagnostic tools we have (audiometry, tinnitus masking), the exact cause often remains unrevealed. Various origins of tinnitus make the treatment very difficult and challenging as well, knowing that tinnitus itself can cause another mental and social troubles.

There are numerous chronic tinnitus treatment methods such as pharmacotherapy, physio‐ therapy, psychotherapy, surgery, etc., which concentrate on the tinnitus intensity reduction and patient's life quality enhancement. Unfortunately, the therapy effect is quite poor in the majority of cases, so alternative modalities of treatment are often introduced. [1] In chronic tinnitus patients, complete disparition of tinnitus arrives very rarely. The number of com‐ pletely cured patients is not statistically significant.

The therapy is targeted to reducing the tinnitus sensation. We evaluate subjective feelings concerning annoyance and loudness of tinnitus described by means of visual analogue scale (VAS 0-10) and objective measurements of the frequency and intensity of tinnitus.

For better tinnitus control, a combination of treatment methods were inducted. The dual approach of Ginkgo biloba extract (EGb 761) and soft laser therapy belongs to various combined methods.

EGb 761 is a standardized extract containing 24% flavonoids, 7% proanthocyanidins, and 6% terpenoids. [2] It has a polymodal effect on the cell and tissue metabolism. The flavonoids are mainly responsible for antioxidant actions while diminishing the free radical damage. [3, 4, 5, 6] The terpenoid fraction contains Ginkolide B which is a potent platelet-activating factor (PAF) receptor antagonist. [7] EGb 761 is also a vasodilator. For hundreds of years the Ginkgo biloba extract was used for the treatment of respiratory disorders. [8] Some studies deny the thera‐ peutic effect of Egb 761 in tinnitus, [2] while others encourage its use. [9]

Laser devices generate electromagnetic radiation with only one wave length. In the biological tissue, the laser light beams exert analgesic, anti-inflammatory, stimulation, thermal, and photochemical effect. The concentrated radiation reduces the irritability of the peripheral nervous system, activates polymorphous cells, monocytes, granulocytes, and fibroblasts, activates respiration chain enzymes, and amplifies anti-oxidative effects in the mitochondria. The laser radiation intensifies metabolism in targeted tissues and cells. They gain additional energy, they can regenerate faster, and their mechanisms of protection are amplified. [10]

In the field of otoneurology, the red light spectrum lasers are the optimal. Thus, the effect we expect is mainly founded on the support of cellular oxidative processes and cell metabolism stimulation.

For the treatment of tinnitus, low level laser therapy (soft laser therapy) has been used since the early 1990s'. Studies concerning the evaluation of its therapeutic possibilities and achieve‐ ments followed soon after. For both single therapy by the soft laser [11, 12, 13] and combined therapy by the soft laser with EGb 761, the results have been discouraging. [14] However, recent researches show more promising results. [15, 16, 17, 18, 19, 20] This mismatch of findings can be clarified by different researchers' approaches, which concern the design of the study, physical parameters of the laser beam, topography of the radiated region, and duration and schedule of the laser therapy. Results from more recent surveys [16, 17] are validated and confirmed by functional magnetic resonance and dosimetric studies.

This study follows our former publication, [21] whereas now involving more patients.

#### **2. Materials and methods**

**Conclusion**: Compared to the outcomes of other studies, our findings reveal a relatively higher percentage of positive changes regarding the tinnitus status and

Tinnitus is described as an illusory sound perceived by the patient when there is no corre‐ sponding source of this sound outside. Tinnitus is present in 5 - 15% of the population and in 70% of patients with hearing disturbances. Tinnitus may signify a disturbance of the peripheral or central part of the hearing system. Beside the hearing system, there are more possible causes of tinnitus - cardiovascular, musculoskeletal, metabolic, and endocrine dysfunctions (dyslipi‐ demia, thyroid dysfunction, diabetes mellitus), and stress and mental disorders might contribute to tinnitus formation as well. Despite the diagnostic tools we have (audiometry, tinnitus masking), the exact cause often remains unrevealed. Various origins of tinnitus make the treatment very difficult and challenging as well, knowing that tinnitus itself can cause

There are numerous chronic tinnitus treatment methods such as pharmacotherapy, physio‐ therapy, psychotherapy, surgery, etc., which concentrate on the tinnitus intensity reduction and patient's life quality enhancement. Unfortunately, the therapy effect is quite poor in the majority of cases, so alternative modalities of treatment are often introduced. [1] In chronic tinnitus patients, complete disparition of tinnitus arrives very rarely. The number of com‐

The therapy is targeted to reducing the tinnitus sensation. We evaluate subjective feelings concerning annoyance and loudness of tinnitus described by means of visual analogue scale

For better tinnitus control, a combination of treatment methods were inducted. The dual approach of Ginkgo biloba extract (EGb 761) and soft laser therapy belongs to various

EGb 761 is a standardized extract containing 24% flavonoids, 7% proanthocyanidins, and 6% terpenoids. [2] It has a polymodal effect on the cell and tissue metabolism. The flavonoids are mainly responsible for antioxidant actions while diminishing the free radical damage. [3, 4, 5, 6] The terpenoid fraction contains Ginkolide B which is a potent platelet-activating factor (PAF) receptor antagonist. [7] EGb 761 is also a vasodilator. For hundreds of years the Ginkgo biloba extract was used for the treatment of respiratory disorders. [8] Some studies deny the thera‐

Laser devices generate electromagnetic radiation with only one wave length. In the biological tissue, the laser light beams exert analgesic, anti-inflammatory, stimulation, thermal, and

(VAS 0-10) and objective measurements of the frequency and intensity of tinnitus.

peutic effect of Egb 761 in tinnitus, [2] while others encourage its use. [9]

greater congruence of objective (audiometric) and subjective (VAS) results.

**Keywords:** Tinnitus, EGb 761, laser

another mental and social troubles.

pletely cured patients is not statistically significant.

**1. Introduction**

160 Update On Hearing Loss

combined methods.

At our ENT Clinic of the Third Medical Faculty, Charles University in Prague, we conducted a simple prospective study including 420 patients with chronic maskable tinnitus between years 1998 and 2006. Two hundred women and 220 men were enrolled, and the mean age of patients was 53.7 years (16 - 77 years). The onset of tinnitus was 3 months to 40 years (mean time of onset 7.7 years) (Table 1).


**Table 1.** Study cohort, demography

In the exclusion criteria otosclerosis, vestibular neurinoma, acute labyrinthine disease, serius cervical spine disorders, and serious or non-compensated metabolic disorders were compre‐ hended.

According to the flow chart of the study, we performed thorough history taking, complex ENT examination, audiologic tests (pure tone audiometry, speech audiometry, if necessary objec‐ tive audiometry as well), tinnitus intensity (dB), and frequency (Hz) determination. The subjective loudness sensation and annoyance were also recorded on visual analogue scale (0- 10 points).

Three weeks before the laser therapy started, patients were instructed to take EGb 761 commercial preparations (Tanakan 80 mg or Tebokan 80 mg, in the form of tablet or drops), three times a day by peroral route of administration. The soft laser therapy followed, using BTL-10 laser device. Patients were scheduled for 10 sessions of laser therapy in at least three weeks, each session lasting 10 minutes. The parameters of the probe were adjusted for 830 nm/ 200 mV, at an energy density 50 J/cm2 . Initially a continuous beam followed by the pulse beam were applied, while the probe was targeted to the mastoid process and external auditory canal (aiming to cochlea).

#### **3. Results**

As to evaluate the changes of tinnitus, both subjective and objective methods were employed: tinnitus intensity and frequency determination (tinnitus masking) and rating on visual analogue scale (VAS). According to VAS, at least one point less was considered as an im‐ provement.

In terms of audiometric changes, the average intensity improvement was found to be 30 dB (range 10-50 dB). One patient described complete disappearance of tinnitus, and one patient noted worsening of his tinnitus by 10 dB. Tinnitus intensity improved by 10 dB in 31 patients, by 20 dB in 73 patients, by 30 dB in 48 patients, by 40 dB in 38 patients, and eventually by 50 dB in 48 patients. The total number of improved cases equals to 238 (Table 2).


**Table 2.** Objective changes in tinnitus masking

Two hundred and thirty-eight cases (56.7 %) achieved improvement in the tinnitus masking, and in 182 cases (43, 7 %) tinnitus masking remained the same. Subjective relief from tinnitus, recorded by VAS questionnaire, was noted in 196 cases (46.7 %) (Table 3). An interesting observation was made in one female patient with objective improvement of 50 dB and no subjective relief from tinnitus.


**Table 3.** Improvement rate

According to the flow chart of the study, we performed thorough history taking, complex ENT examination, audiologic tests (pure tone audiometry, speech audiometry, if necessary objec‐ tive audiometry as well), tinnitus intensity (dB), and frequency (Hz) determination. The subjective loudness sensation and annoyance were also recorded on visual analogue scale (0-

Three weeks before the laser therapy started, patients were instructed to take EGb 761 commercial preparations (Tanakan 80 mg or Tebokan 80 mg, in the form of tablet or drops), three times a day by peroral route of administration. The soft laser therapy followed, using BTL-10 laser device. Patients were scheduled for 10 sessions of laser therapy in at least three weeks, each session lasting 10 minutes. The parameters of the probe were adjusted for 830 nm/

were applied, while the probe was targeted to the mastoid process and external auditory canal

As to evaluate the changes of tinnitus, both subjective and objective methods were employed: tinnitus intensity and frequency determination (tinnitus masking) and rating on visual analogue scale (VAS). According to VAS, at least one point less was considered as an im‐

In terms of audiometric changes, the average intensity improvement was found to be 30 dB (range 10-50 dB). One patient described complete disappearance of tinnitus, and one patient noted worsening of his tinnitus by 10 dB. Tinnitus intensity improved by 10 dB in 31 patients, by 20 dB in 73 patients, by 30 dB in 48 patients, by 40 dB in 38 patients, and eventually by 50

Two hundred and thirty-eight cases (56.7 %) achieved improvement in the tinnitus masking, and in 182 cases (43, 7 %) tinnitus masking remained the same. Subjective relief from tinnitus, recorded by VAS questionnaire, was noted in 196 cases (46.7 %) (Table 3). An interesting observation was made in one female patient with objective improvement of 50 dB and no

13.0 30.6 20.2 16.0 20.2

dB in 48 patients. The total number of improved cases equals to 238 (Table 2).

**Change Count %**

∑ 238 100.0

**Table 2.** Objective changes in tinnitus masking

subjective relief from tinnitus.

. Initially a continuous beam followed by the pulse beam

10 points).

162 Update On Hearing Loss

(aiming to cochlea).

**3. Results**

provement.

by 10 dB by 20 dB by 30 dB by 40 dB by 50 dB

200 mV, at an energy density 50 J/cm2

The correlation of subjective and objective measurements was following: in 79% of findings total accord was found (conformity of audiogram and VAS questionnaire), in 11% of cases no subjective improvement was reported in patients with objective audiometrical improvement, and in the remaining 10% of cases, subjective relief from tinnitus was not supported by any objective finding in audiogram (Table 4).


**Table 4.** Correlation of subjective and objective evaluation

#### **4. Discussion**

For the tinnitus evaluation, we can never rely solely on the objective measurement tools. Many relevant factors cannot be measured, but only perceived by the patients. Tinnitus is a very subjective sound sensation, and each person feels it in his own individual way. Hence, the subjective assessment is for us as significant as objective audiometric tests. In our study, regardless the audiometric results, 46.7% of patients described a certain level of relief. The objective tests revealed that an even higher number - 56.7% - of patients displayed improve‐ ment with a relatively high mean value of 30dB. Audiometric intensity determination ap‐ proved the patients' subjective records in 79% of cases, which indicates the relevance of both methods.

The study results are in accord with our everyday experience, when tinnitus intensity deter‐ mination (tinnitus masking) changes are not always perceived the same way by the patient. In our study cohort 10% of patients reported diminished tinnitus perception, although the audiometric tests showed no change. This might be explicated by the placebo effect. Contra‐ riwise, 11% of the cases were not aware of their "audiologic improvement," which is a routinely described phenomenon of central processing or imprinting of tinnitus. [22, 23]

The therapy was supported well, no serious adverse events were reported, but some patients complained of the laser's thermal effect though.

In comparison to other researches concentrating on soft laser therapy in chronic tinnitus, Shiomi et al. [11] conducted a similar design study but with no premedication by EGb 761. Finally, he declared similar results in chronic tinnitus patients as we did. In a double-blind randomized study of Gungor et al. [18] who also used laser therapy alone (power of 5 mW, 650 nm wavelength, 15 minutes for one session), the results were similar as in our study. However, Rogowski et al. [13] and Partheniadis-Stumpf et al. [14] found out rather negative outcomes. Such a difference could be explained by different laser parameters and different number of patients in study groups. Compared to the German study, [14] we applied Egb 761 perorally three weeks before the laser therapy, expecting accentuation of the nootropic effect with a longer time of administration, while Partheniadis-Stumpf et al. [14] applied Egb 761 intravenously directly before each laser session.

#### **5. Conclusion**

Patients suffering from chronic tinnitus often try numerous therapeutic modalities in a search for alleviation of the stress and annoyance caused by their illness. According to our study results, a combination of Egb 761 and soft laser therapy can be recommended as a safe and suitable modality in the treatment of chronic maskable tinnitus.

#### **6. Disclosure statement**

This manuscript has never been submitted for a publication. It is related to, and might be considered as an extension of a previous work, which has been published as:

Hahn, A., Schalek, P., Šejna, I., Rosina, J. (2012). Combined tinnitus therapy with laser and EGb 761: further experiences. Int. Tinnitus J. 17 (1), 50-53

The authors deny any possible conflict of interest related to individual authors' commitments, project support or financial relationships of the authors.

"No competing financial interests exist."

#### **Author details**

Klára Procházková1\*, Ivan Šejna1 , Petr Schalek1 , Jozef Rosina2 and Aleš Hahn1

\*Address all correspondence to: klara.prochazkova@gmail.com

1 Department of Otorhinolaryngology of the Third Faculty of Medicine, Charles University Prague, Czech Republic

2 Department of Medical Biophysics and Informatics of the Third Faculty of Medicine, Charles University Prague, Czech Republic

#### **References**

Finally, he declared similar results in chronic tinnitus patients as we did. In a double-blind randomized study of Gungor et al. [18] who also used laser therapy alone (power of 5 mW, 650 nm wavelength, 15 minutes for one session), the results were similar as in our study. However, Rogowski et al. [13] and Partheniadis-Stumpf et al. [14] found out rather negative outcomes. Such a difference could be explained by different laser parameters and different number of patients in study groups. Compared to the German study, [14] we applied Egb 761 perorally three weeks before the laser therapy, expecting accentuation of the nootropic effect with a longer time of administration, while Partheniadis-Stumpf et al. [14] applied Egb 761

Patients suffering from chronic tinnitus often try numerous therapeutic modalities in a search for alleviation of the stress and annoyance caused by their illness. According to our study results, a combination of Egb 761 and soft laser therapy can be recommended as a safe and

This manuscript has never been submitted for a publication. It is related to, and might be

Hahn, A., Schalek, P., Šejna, I., Rosina, J. (2012). Combined tinnitus therapy with laser and EGb

The authors deny any possible conflict of interest related to individual authors' commitments,

1 Department of Otorhinolaryngology of the Third Faculty of Medicine, Charles University

2 Department of Medical Biophysics and Informatics of the Third Faculty of Medicine,

, Jozef Rosina2

and Aleš Hahn1

considered as an extension of a previous work, which has been published as:

, Petr Schalek1

\*Address all correspondence to: klara.prochazkova@gmail.com

intravenously directly before each laser session.

suitable modality in the treatment of chronic maskable tinnitus.

761: further experiences. Int. Tinnitus J. 17 (1), 50-53

"No competing financial interests exist."

Charles University Prague, Czech Republic

Klára Procházková1\*, Ivan Šejna1

**Author details**

Prague, Czech Republic

project support or financial relationships of the authors.

**5. Conclusion**

164 Update On Hearing Loss

**6. Disclosure statement**


**Section 5**

**Hearing Screening**

[15] Tauber, S., Baumgartner, R., Schorn, K., Beyer, W. (2001). Lightdosimetric quantita‐ tive analysis of the human petrous bone: experimental study for laser irradiation of

[16] Tauber, S., Schorn, K., Beyer, W., Baumgartner, R. (2003). Transmeatal cochlear laser (TCL) treatment of cochlear dysfunction: a feasibility study for chronic tinnitus. La‐

[17] Siedentopf, C.M., Ischebeck, A., Haala, I.A. et al. (2007). Neural correlates of trans‐ meatal cochlear laser (TCL) stimulation in healthy human subjects. Neurosci. Lett.

[18] Gungor, A., Dogru, S., Cincik, H., Erkul, E., Poyrazoglu, E. (2007). Effectiveness of transmeatal low power laser irradiation for chronic tinnitus. J Laryngol Otol. 12, 1-5.

[19] Salahaldin, A. H., Abdulhadi, K., Najjar, N., Bener, A. (2012). Low-level laser therapy in patients with complaints of tinnitus: a clinical study. ISRN, Otolaryngol, Article ID

[20] Okhovat, A., Nezamoddin, B., Okhovat, H., Malekpour, A., Abtahi, H. (2011). Lowlevel laser for treatment of tinnitus: a self-controlled clinical trial. J Res Med Sci 16(1),

[21] Hahn, A., Schalek, P., Šejna, I., Rosina, J. (2012). Combined tinnitus therapy with la‐

[22] Shulman, A., Goldstein, B. (2006). Tinnitus dyssynchrony-synchrony theory: a trans‐ lational concept for diagnosis and treatment. Int Tinnitus J. 12(2), 101-114.

[23] Jastreboff, P.J., Hazell, J.W.P. (1993). A neurophysiological approach to tinnitus: clini‐

ser and EGb 761: further experiences. Int Tinnitus J. 17(1), 50-53.

cal implications. Br J Audiol. 27, 7-17.

the cochlea. Lasers Surg Med. 28(1), 18-26.

sers Med Sci. 18(3), 154-161.

411(3), 189-193.

132060.

166 Update On Hearing Loss

33-38.

## **Technological Advances in Universal Neonatal Hearing Screening (UNHS)**

Stavros Hatzopoulos, Henryk Skarzynski and Piotr H Skarzynski

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/61178

#### **Abstract**

Within the last decade, numerous new challenges have appeared in the UNHS arena, such as (i) the need to validate the automated OAE/ABR screeners; (ii) the need to qualify the responses from the automated devices; (iii) the need to obtain additional information (i.e., hearing threshold) for the subject under assessment, in a short period of time; (iv) and the need to integrate numerous measurements in a single portable automated device. To respond to these clinical demands, several new methodologies have been introduced to the UNHS clinical practice. In this context, the aim of this chapter is to provide infor‐ mation on these new technological trends.

**Keywords:** Automated otoacoustic emissions (AOAE), automated auditory brainstem re‐ sponse (AABR), wideband reflectance, middle ear power analysis, neonatal hearing screening, auditory state steady response, hearing threshold

#### **1. Introduction**

Otoacoustic emissions (OAEs) or cochlear echoes is a term coined by David Kemp in 1978 [1], describing the transient responses from the inner ear, upon its stimulation by an acoustic click stimulus. During the last 20 years, OAE protocols have been used in many areas of audiology and hearing science [2]. The most significant contribution of OAEs is in the area of universal neonatal hearing screening (UNHS).

While the main objective of neonatal hearing screening (NHS) is the identification of infants with a hearing deficit (≥30 dB HL), the objectives of a UNHS program have a broader vision. Two important phases are considered: (i) the identification of infants with mild and moderate hearing deficits and (ii) an intervention in terms of hearing improvement (hearing aids and

© 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

cochlear implants) and neural rehabilitation, aiming at the restoration of hearing and the normalization of the quality of life of the young patient.

Within the last decade, numerous new challenges have appeared in the UNHS arena, such as (i) the need to validate the automated OAE/ABR screeners; (ii) the need to qualify the responses from the automated devices; (iii) the need to obtain additional information (i.e., hearing threshold) for the subject under assessment, in a short period of time; and (iv) the need to integrate numerous measurements in a single portable automated device. To respond to these clinical demands, several new methodologies have been introduced to the UNHS clinical practice. In this context, the aim of this chapter is to provide information on these new technological trends.

#### **2. Automated auditory brainstem responses**

In the early 2002, the first fourth-generation OAE devices appeared in the market and offered the possibility to integrate information from different testing protocols such as automated OAE (AOAE) and automated ABR (AABR) responses. The combined screening protocols (AOAE + AABR) targeted the identification of auditory neuropathy, most prevalent in the neonatal intensive care (NICU) environment.

With the introduction of the AABR protocols in the NHS programs, several issues became evident, and among those questions related to screening times and screening costs. The latter is outside the objectives of this paper and will not be addressed. A previous study of our group, in the context of the regional NHS project CHEAP in Emilia-Romagna, Italy [3], provided evidence suggesting that in terms of time-requirements, portable ABR (Audioscreener, Viasys; Accuscreen, GN-Otometrics; Algo 3i, Natus) and OAE devices were converging to the same time values. Data from the above study suggested that (i) the average time for AOAE responses is less than 10 s in a cooperative subject and less that 120 s (2 min) in non-cooperative subjects and (ii) the average AABR test times were less than 120 s, while longer times (600 s per ear) were required for uncooperative subjects. The placement of the AABR electrodes might be a complicated process, especially when highly skin impedances (caused by excessive lipid layers) are encountered. In these cases, the AABR algorithms tend to oversample in order to derive a coherent signal, and as a result, the testing times are significantly prolonged.

A combined two-stage approach (i.e., AOAE + AABR) eliminates the risk of not identifying infants with auditory neuropathy and assures that the screening sensitivity is high. Contrary to this hypothesis, data from a large-scale American study by White et al. [4] suggest that this is not always the case. From 86,634 screened infants, using a two-stage OAE/A-ABR protocol, 23% would have passed the AABR.

Another interesting development in the ABR/AABR area is in the area of the evoking stimulus. Traditionally, ABR and AABR protocols use click stimuli to synchronize as many neural fibers as possible and to obtain an ABR response of large amplitude with less sweeps. Recently, chirp stimuli have been used to optimize the ABR/AABR responses. According to Kristensen and Elberling [5], "Upward chirps are often designed to compensate for the cochlear traveling wave delay which is regarded as independent of stimulation level. A chirp based on a traveling wave model is therefore referred to as a level-independent chirp. Another compensation strategy, for instance based on frequency-specific auditory brainstem response (ABR) latencies, results in a chirp that changes with stimulation level and is therefore referred to as a level-dependent chirp. One such strategy, the direct approach, results in a chirp family that is called the levelspecific chirp." Data from studies using level-dependent chirps [6–11] are very encouraging, reporting ABRs recorded in less time and with higher amplitude values. The latter is very important for the statistical algorithms of the AABR devices, meaning that higher statistical accuracy can be obtained in the chirp-evoked AABRs.

### **3. Middle ear reflectance and Middle Ear Power Analysis (MEPA)**

cochlear implants) and neural rehabilitation, aiming at the restoration of hearing and the

Within the last decade, numerous new challenges have appeared in the UNHS arena, such as (i) the need to validate the automated OAE/ABR screeners; (ii) the need to qualify the responses from the automated devices; (iii) the need to obtain additional information (i.e., hearing threshold) for the subject under assessment, in a short period of time; and (iv) the need to integrate numerous measurements in a single portable automated device. To respond to these clinical demands, several new methodologies have been introduced to the UNHS clinical practice. In this context, the aim of this chapter is to provide information on these new

In the early 2002, the first fourth-generation OAE devices appeared in the market and offered the possibility to integrate information from different testing protocols such as automated OAE (AOAE) and automated ABR (AABR) responses. The combined screening protocols (AOAE + AABR) targeted the identification of auditory neuropathy, most prevalent in the neonatal

With the introduction of the AABR protocols in the NHS programs, several issues became evident, and among those questions related to screening times and screening costs. The latter is outside the objectives of this paper and will not be addressed. A previous study of our group, in the context of the regional NHS project CHEAP in Emilia-Romagna, Italy [3], provided evidence suggesting that in terms of time-requirements, portable ABR (Audioscreener, Viasys; Accuscreen, GN-Otometrics; Algo 3i, Natus) and OAE devices were converging to the same time values. Data from the above study suggested that (i) the average time for AOAE responses is less than 10 s in a cooperative subject and less that 120 s (2 min) in non-cooperative subjects and (ii) the average AABR test times were less than 120 s, while longer times (600 s per ear) were required for uncooperative subjects. The placement of the AABR electrodes might be a complicated process, especially when highly skin impedances (caused by excessive lipid layers) are encountered. In these cases, the AABR algorithms tend to oversample in order to

derive a coherent signal, and as a result, the testing times are significantly prolonged.

A combined two-stage approach (i.e., AOAE + AABR) eliminates the risk of not identifying infants with auditory neuropathy and assures that the screening sensitivity is high. Contrary to this hypothesis, data from a large-scale American study by White et al. [4] suggest that this is not always the case. From 86,634 screened infants, using a two-stage OAE/A-ABR protocol,

Another interesting development in the ABR/AABR area is in the area of the evoking stimulus. Traditionally, ABR and AABR protocols use click stimuli to synchronize as many neural fibers as possible and to obtain an ABR response of large amplitude with less sweeps. Recently, chirp stimuli have been used to optimize the ABR/AABR responses. According to Kristensen and

normalization of the quality of life of the young patient.

**2. Automated auditory brainstem responses**

intensive care (NICU) environment.

23% would have passed the AABR.

technological trends.

170 Update On Hearing Loss

Data from studies that have evaluated the performance of NHS programs in the well-baby clinic or in the NICU [4, 12, 13] have reported that the majority of "screening refers" are due to transmission impeding factors such as the amniotic fluid or any substance blocking the propagation of the acoustic stimulus. Usually, these conditions are transient (i.e., they last 24– 30 h), and infants can pass the OAE test when the fluid is absorbed or when the auditory meatus is clean.

Using a middle ear power analysis (MEPA) testing procedure, it is possible to determine whether the middle ear conducts properly acoustic stimuli, and in this context, the OAE screening results can be interpreted more clearly. Data from the literature [14, 15] have shown that one of the MEPA metrics, the middle ear reflectance, is more sensitive to the distortion product OAE (DPOAE) status than the 1-kHz tympanometry values. Power reflectance is a measure of middle ear inefficiency. It is the ratio or percentage of power reflected from the eardrum to the incident power as a function of frequency. Acoustic power measurements objectively quantify middle ear function or malfunction.

Currently, there is only one manufacturer (Mimosa Acoustics) offering reflectance measure‐ ments. The company offers two devices capable of MEPA, DPOAE, and general OAE meas‐ urements: the Otostat (handheld) and the HearID (research oriented) model. These devices (depicted in Figure 1) can measure wideband power reflectance up to 6 kHz and most importantly without the need for a pressurized ear canal.

To interpret the clinical usefulness of the MEPA approach, Hunter et al. [15] constructed normative regions for newborns, relating middle ear reflectance values evoked by chirp stimuli and DPOAE amplitudes at 1.0, 1.5, 2.0, 3.0, 4.0, and 6.0 kHz. The three regions were described as follows:


**Figure 1.** The Mimosa Acoustic devices capable of recording wideband reflectance and OAEs. Data from the Mimosa Acoustics website (http://www.mimosaacoustics.com).

These areas are depicted in Figure 2. In terms of interpretation, If the MEPA reflectance values fall above the "pass" area, especially around 2 kHz, outer or middle ear problems may be the cause, and a rescreening session after a few hours or a day is recommended prior to diagnostic referral. If the outcome is still a "refer" then clinical assessment is necessary. If the MEPA reflectance values fall within the "pass" area, especially around 2 kHz, the middle ear is more likely to be normal and associated with a DPOAE pass result. If the DPOAE result is ambiguous or a "refer", then middle ear issues are not suspected as a hearing deficit cause and further clinical assessment is necessary. Table 1 summarizes all these outcomes.

**Figure 2.** Pass, ambiguous, and retest regions for wideband reflectance using chirp (solid regions) and sine (symbols) stimuli. Results above this region, especially at 2 kHz, are associated with false-positive DPOAE refer results. Data from the Mimosa Acoustics website and from Hunter et al. (2010).


**Table 1.** How to interpet distortion product OAEs and reflectance results in newborns (from http:// www.mimosaacoustics.com).

These areas are depicted in Figure 2. In terms of interpretation, If the MEPA reflectance values fall above the "pass" area, especially around 2 kHz, outer or middle ear problems may be the cause, and a rescreening session after a few hours or a day is recommended prior to diagnostic referral. If the outcome is still a "refer" then clinical assessment is necessary. If the MEPA reflectance values fall within the "pass" area, especially around 2 kHz, the middle ear is more

**Figure 1.** The Mimosa Acoustic devices capable of recording wideband reflectance and OAEs. Data from the Mimosa

Acoustics website (http://www.mimosaacoustics.com).

172 Update On Hearing Loss

### **4. Auditory Steady-State Responses (ASSR)**

OAE and ABR testing procedures are evoked by electrical transient stimuli (clicks, filtered clicks, etc.), and as a result, the responses are correlated with a few audiometric frequencies, which correspond to the maximum spectral content of the stimulus (around 2.0 kHz). Con‐ sidering this clinical setup, there are other protocols that could be candidates for a hearing assessment of neonates, children, and adults. Among those is the electrocochleography (EcoG), the middle latency (ML) responses, and the most recently reported steady-state responses (SSR). The first two approaches can be excluded because they require long times either for the position of an intratympanic electrode or for sampling purposes. The last protocol has shown a good potential for hearing screening since with an adequate manipulation of the stimulus modulation frequency, one can record responses or from the auditory cortex (low modulation frequencies around 40 Hz) or from the brainstem (frequencies around 50–120 Hz) [16–18]. The basic SSR protocol has evolved into an automated procedure (ASSR) where multiple stimulus frequencies are used and regression models predict hearing levels at the tested stimuli. The ASSR protocols have been greatly optimized for lower frequency stimuli such as 500 Hz [19].

In 2002, Conne-Wesson et al. [16] suggested that it could be possible to use an SSR protocol in a Neonatal Hearing Program, and since the SSR responses were generated by the brainstem for modulation frequencies >40 Hz, the ASSR could substitute the AABR [20–22]. In the referenced studies, a good agreement has been reported between the ASSR and the AABR responses at 2.0 kHz and various significant differences at 0.5, 1.0, and 4.0 kHz. The available data suggest that the AASR protocols should be developed further to become more independ‐ ent of various clinical factors (related to the tested subject and to the stimuli used) and should be applied on a large population of subjects so that the results can be easily used clinically.

The important factors affecting the AABR responses (i.e., the ambient noise and the skinelectrode impedance) interfere also with the ASSR recordings. In 2010, Vivosonic presented a new family of devices (called amplitrodes) using a novel approach. Each scalp electrode was connected to a small preamplifier within the electrode assembly. Amplifying the signal in situ has many advantages, such as the suppression of the ambient noise and the elevation of the signal-to-noise ratio (S/N). This approach results in clean AABR and ASSR traces. One of the issues reported since its release, is that the new electrodes require very often a change of the electrode batteries.

In the context of a neonatal screening, an ASSR screening protocol can focus on discrete frequency points (i.e., 1.0 and 2.0 kHz or 2.0 and 4.0 kHz), which show relative immunity to ambient noise, as shown in the neonatal data in Figures 3A and 3B. One of the problems of the early ASSR devices (Audera by Viasys; Master by Natus) was that the mean hearing threshold estimates were characterized by large variance. Recent data in the literature and specifically from the Audix equipment developers (Neuronic) report significant advances both in terms of software and hardware and a superior performance of a multiple SSR protocol to the conventional ABR [23, 24].

**4. Auditory Steady-State Responses (ASSR)**

174 Update On Hearing Loss

electrode batteries.

conventional ABR [23, 24].

OAE and ABR testing procedures are evoked by electrical transient stimuli (clicks, filtered clicks, etc.), and as a result, the responses are correlated with a few audiometric frequencies, which correspond to the maximum spectral content of the stimulus (around 2.0 kHz). Con‐ sidering this clinical setup, there are other protocols that could be candidates for a hearing assessment of neonates, children, and adults. Among those is the electrocochleography (EcoG), the middle latency (ML) responses, and the most recently reported steady-state responses (SSR). The first two approaches can be excluded because they require long times either for the position of an intratympanic electrode or for sampling purposes. The last protocol has shown a good potential for hearing screening since with an adequate manipulation of the stimulus modulation frequency, one can record responses or from the auditory cortex (low modulation frequencies around 40 Hz) or from the brainstem (frequencies around 50–120 Hz) [16–18]. The basic SSR protocol has evolved into an automated procedure (ASSR) where multiple stimulus frequencies are used and regression models predict hearing levels at the tested stimuli. The ASSR protocols have been greatly optimized for lower frequency stimuli such as 500 Hz [19].

In 2002, Conne-Wesson et al. [16] suggested that it could be possible to use an SSR protocol in a Neonatal Hearing Program, and since the SSR responses were generated by the brainstem for modulation frequencies >40 Hz, the ASSR could substitute the AABR [20–22]. In the referenced studies, a good agreement has been reported between the ASSR and the AABR responses at 2.0 kHz and various significant differences at 0.5, 1.0, and 4.0 kHz. The available data suggest that the AASR protocols should be developed further to become more independ‐ ent of various clinical factors (related to the tested subject and to the stimuli used) and should be applied on a large population of subjects so that the results can be easily used clinically.

The important factors affecting the AABR responses (i.e., the ambient noise and the skinelectrode impedance) interfere also with the ASSR recordings. In 2010, Vivosonic presented a new family of devices (called amplitrodes) using a novel approach. Each scalp electrode was connected to a small preamplifier within the electrode assembly. Amplifying the signal in situ has many advantages, such as the suppression of the ambient noise and the elevation of the signal-to-noise ratio (S/N). This approach results in clean AABR and ASSR traces. One of the issues reported since its release, is that the new electrodes require very often a change of the

In the context of a neonatal screening, an ASSR screening protocol can focus on discrete frequency points (i.e., 1.0 and 2.0 kHz or 2.0 and 4.0 kHz), which show relative immunity to ambient noise, as shown in the neonatal data in Figures 3A and 3B. One of the problems of the early ASSR devices (Audera by Viasys; Master by Natus) was that the mean hearing threshold estimates were characterized by large variance. Recent data in the literature and specifically from the Audix equipment developers (Neuronic) report significant advances both in terms of software and hardware and a superior performance of a multiple SSR protocol to the

**Figure 3.** A) ASSR responses from a non-cooperative infant, using the AUDERA ASSR device (VIASYS). Responses at 500 Hz were not available due to noise caused by myogenic artifacts. The ASSR recording time was 14 min longer that the AABR test, resulting as 22 min. The large size of the error bars, at 2.0 and 4 kHz, show threshold means at 60 and 55 dB HL, but the variability of the measurements makes the threshold prediction difficult to be considered. (B) ASSR response from another well-baby infant, using the same ASSR device. The ASSR recording was also significantly lon‐ ger than the AABR response (16 vs. 7 min). The error bars around the threshold average (indicated by an "x") are small and the prediction can be considered practical. For example, at 1.0 kHz, the threshold level is shown at 55 dB with a 95% probability that it will be in the interval 35–65 dB HL. The latter estimates are derived from the values of the error bars.

Recently, a study by Ciorba et al. [25] presented data on the relationship between ABR, ASSR estimates, and data from Conditioned Orientation Responses (COR), a technique widely diffused in the intervention phase of many UNHS programs. The data suggested a very good relationship between the outcomes of the ASSR and the COR techniques, with the ASSR data being closer to the ABR estimates. Data from large-scale studies along this direction (i.e., comparing ASSR with other protocols) could support this hypothesis and eliminate the use of ABR and COR in this intervention step.

#### **5. Threshold estimation via DPOAE measurements**

From the early nineties, where OAEs were accepted in the clinical practice, the relationship between hearing threshold and OAE responses received a lot of attention [26–28]. What previous research suggests is that in cases presenting sensorineural deficits (i.e., excluding conductive and retrocochlear causes), there is a good agreement between the OAE respond levels and the hearing threshold. In this context, distortion product OAE (DPOAE) protocols can provide additional information [26, 29–31]. Input–output (or I/O functions) DPOAE protocols provide information on the relationship between the evoking stimulus and the signal compression of the cochlear amplifier. Data supporting this hypothesis are derived from animal experiments (furosemide intoxication) [32] and clinical human studies from cases presenting sensorineural deficits [29, 33–34]. When the hearing loss is increased, the slope of the corresponding DPOAE I/O-functions decreases and reveals a loss of compression in the cochlear amplifier. Using various setups of the DPOAE I/O stimuli, one can estimate the cochlear compression, which is related to a specific threshold value [31, 35]. Janssen et al. [36] used this concept to produce a relationship between DPOAE I/O amplitude values and hearing threshold. According to their data, "The hearing threshold was found to be increasing within the early postnatal period (average age: 3 days), predominantly at the higher frequencies, and to be normalized in a follow-up measurement (after four weeks). However, the slope of the DPOAE I/O-functions obtained in the first and second measurement was unchanged revealing normal cochlear compression. Consequently, these findings were interpreted as temporary conductive hearing losses due to the presence of amniotic fluid and/or Eustachian tube dysfunction." The value of cochlear compression changes when the middle ear stimulus pathway is affected. Therefore, this procedure has the theoretical potential to discriminate middle from inner ear deficits. Data from the literature have not validated yet this hypothesis.

The research findings from Janssen et al. [36] and Gorga et al. [35] have been commercialized by Natus in the Cochlea-Scan device [37]. Hearing threshold can be extrapolated up to values relative to 50 dB HL in the frequency range from 1.5 to 6 kHz. Figure 4 shows a typical hearing threshold profile and the corresponding Cochlea-Scan-mediated estimation of hearing threshold. At present, the Cochlea-Scan device offers a platform for a third-generation OAE testing (TEOAEs and DPOAEs), I/O DPOAE estimation with hearing threshold extrapolation.

Further analyses [38, 39] on the efficacy of the Cochlea-Scan DPOAE algorithm, relating hearing threshold data and Cochlea-Scan estimated thresholds from a group of adult sensor‐ Technological Advances in Universal Neonatal Hearing Screening (UNHS) http://dx.doi.org/10.5772/61178 177

Recently, a study by Ciorba et al. [25] presented data on the relationship between ABR, ASSR estimates, and data from Conditioned Orientation Responses (COR), a technique widely diffused in the intervention phase of many UNHS programs. The data suggested a very good relationship between the outcomes of the ASSR and the COR techniques, with the ASSR data being closer to the ABR estimates. Data from large-scale studies along this direction (i.e., comparing ASSR with other protocols) could support this hypothesis and eliminate the use of

From the early nineties, where OAEs were accepted in the clinical practice, the relationship between hearing threshold and OAE responses received a lot of attention [26–28]. What previous research suggests is that in cases presenting sensorineural deficits (i.e., excluding conductive and retrocochlear causes), there is a good agreement between the OAE respond levels and the hearing threshold. In this context, distortion product OAE (DPOAE) protocols can provide additional information [26, 29–31]. Input–output (or I/O functions) DPOAE protocols provide information on the relationship between the evoking stimulus and the signal compression of the cochlear amplifier. Data supporting this hypothesis are derived from animal experiments (furosemide intoxication) [32] and clinical human studies from cases presenting sensorineural deficits [29, 33–34]. When the hearing loss is increased, the slope of the corresponding DPOAE I/O-functions decreases and reveals a loss of compression in the cochlear amplifier. Using various setups of the DPOAE I/O stimuli, one can estimate the cochlear compression, which is related to a specific threshold value [31, 35]. Janssen et al. [36] used this concept to produce a relationship between DPOAE I/O amplitude values and hearing threshold. According to their data, "The hearing threshold was found to be increasing within the early postnatal period (average age: 3 days), predominantly at the higher frequencies, and to be normalized in a follow-up measurement (after four weeks). However, the slope of the DPOAE I/O-functions obtained in the first and second measurement was unchanged revealing normal cochlear compression. Consequently, these findings were interpreted as temporary conductive hearing losses due to the presence of amniotic fluid and/or Eustachian tube dysfunction." The value of cochlear compression changes when the middle ear stimulus pathway is affected. Therefore, this procedure has the theoretical potential to discriminate middle from inner ear deficits. Data from the literature have not validated yet this hypothesis.

The research findings from Janssen et al. [36] and Gorga et al. [35] have been commercialized by Natus in the Cochlea-Scan device [37]. Hearing threshold can be extrapolated up to values relative to 50 dB HL in the frequency range from 1.5 to 6 kHz. Figure 4 shows a typical hearing threshold profile and the corresponding Cochlea-Scan-mediated estimation of hearing threshold. At present, the Cochlea-Scan device offers a platform for a third-generation OAE testing (TEOAEs and DPOAEs), I/O DPOAE estimation with hearing threshold extrapolation.

Further analyses [38, 39] on the efficacy of the Cochlea-Scan DPOAE algorithm, relating hearing threshold data and Cochlea-Scan estimated thresholds from a group of adult sensor‐

ABR and COR in this intervention step.

176 Update On Hearing Loss

**5. Threshold estimation via DPOAE measurements**

**Figure 4.** Cochlea-Scan data in comparison to behavioral threshold levels, from an adult subject. Top panel: Cochlea-Scan responses and threshold estimation from the right ear; middle panel: behavioral data; bottom panel: Cochlea-Scan responses and threshold estimation from the left ear. The Cochlea-Scan panels report the estimated threshold values per frequency. The acronym "NA" means that at the specific frequency no threshold estimation was possible.

ineural cases, suggested a different scenario than the one proposed initially by Janssen et al. [36]. In the Hatzopoulos et al. [39] study, behavioral and Cochlea-Scan data were analyzed with logistic regression models in order to find the probability (≤0.9) of a robust DPOAE response at 2.0, 3.0, and 4.0 kHz. The data suggested that the maximum behavioral levels where valid DPOAEs could be detected were equal to of 32.8, 21, and 34 dB, respectively. For normal hearing adults, the detection levels were lower. Figures 5 and 6 depict the relationship between behavioral data (at 2.0, 3.0, and 4.0 kHz) and Cochlea-Scan estimates from the cases presenting hearing loss. For example, in Figure 5 and for 2.0 kHz, a probability of 90% Cochlea-Scan response detection corresponds to a threshold approximately of 15 dB HL. In this context, it is still possible to have a detection threshold as high as 50 dB HL. The corresponding proba‐ bility falls below 30% and, as such, limits the usefulness of the Cochlea-Scan protocol

**Figure 5.** Logistic regression model for normal hearing threshold Cochlea-Scan data at 2.0 and 3.0 kHz. The equation relating the two variables (c = Cochlea-Scan; p = behavioral threshold) is shown at the top of each graph. The *x* axis shows behavioral threshold in dB HL and the *y* axis the probability of a Cochlea-Scan response. For a fixed response probability of 90%, the detectable threshold level is approximately 15 and 20 dB HL, for the data at 2.0 and 3.0 kHz. This implies that in order to obtain a Cochlea-Scan response for a 50-dB HL hearing threshold, the probability of find‐ ing a true response drops to 40% and 10%, respectively (for 2.0 and 3.0 kHz).

**Figure 6.** Logistic regression model for normal hearing threshold Cochlea-Scan data at 4.0 kHz. The equation relating the two variables (c = Cochlea-Scan; p = behavioral threshold) is shown at the top of each graph. The *x* axis shows behavioral threshold in dB HL and the *y* axis the probability of a Cochlea-Scan response. For a fixed response probabil‐ ity of 90%, the detectable threshold level is approximately 35 dB HL. For a 50-dB HL threshold, the probability of a true response drops to 15%. The relationship between the behavioral and the Cochlea-Scan data at 4.0 kHz is opti‐ mized, but the sensitivity of the method drops very quickly as we move to higher thresholds 35 dB HL.

The authors at this point in time could not verify if Natus has intentions of developing further this product. Cochlea-Scan threshold estimation could be greatly improved by introducing changes in the device's algorithms related to (i) the sample size, which was used to calibrate the prototype device. Sampling a larger population can minimize the variance of the average DPOAE amplitude per tested frequency (ii) by inserting correction factors in the algorithm, which extrapolates DPOAE amplitudes to hearing levels. Janssen et al. [36] have used a linear regression model to achieve this, but higher-order models (quadratic, cubic) can offer higher precision in the threshold estimation.

#### **6. Integration of multiple hearing assessment protocols into an automated device**

**Figure 5.** Logistic regression model for normal hearing threshold Cochlea-Scan data at 2.0 and 3.0 kHz. The equation relating the two variables (c = Cochlea-Scan; p = behavioral threshold) is shown at the top of each graph. The *x* axis shows behavioral threshold in dB HL and the *y* axis the probability of a Cochlea-Scan response. For a fixed response probability of 90%, the detectable threshold level is approximately 15 and 20 dB HL, for the data at 2.0 and 3.0 kHz. This implies that in order to obtain a Cochlea-Scan response for a 50-dB HL hearing threshold, the probability of find‐

ing a true response drops to 40% and 10%, respectively (for 2.0 and 3.0 kHz).

178 Update On Hearing Loss

The success of the NHS screening practices challenged another area of pediatric audiology, the area of schoolchildren screening. Data from large-scale screening programs, as in Poland, suggested that in this area different protocols could be applied than in UNHS programs, with emphasis on pure tone behavioral responses, tympanometry, and ABR [40]. The OAEs were found the less effective tool in the battery of screening tests, suffering mainly from the ambient noise present in schools.

Recently, the fifth-generation OAE equipment appeared in the market. A number of OAE manufacturers (Natus, Path Medical solutions) proposed handheld devices capable of testing subjects with OAEs/AOAEs, AABR, and ASSR. A tympanometry assessment has not appeared so far due to complications in the probe of the device (canal pressurization issues). Mimosa Acoustics offers wide-reflectance measurements (which can substitute acoustic immittance) and OAEs but not evoked potentials.

The proposal from Path Medical Solutions (model: Sentiero—advanced) is a device capable not only of AOAE/AABR/ASSR protocols but also of protocols for speech Audiometry. The device is depicted in Figure 7. Such a device can be easily implemented in both phases (identification and intervention) of a UNHS program, and it is hoped that other manufacturers will follow this protocol-integration trend.

**Figure 7.** The Sentiero Advanced device (data from the website of Path medical solutions http://www.pathme.de).

#### **7. Conclusions**

During the last 10–15 years, significant advances have been made toward the integration of various protocols and technologies in UNHS strategies. The most important contribution is in the area of auditory steady-state responses, which has been shown to be well correlated with other metrics in audiology such as the AABR, ABR, OAEs, and COR. The current technological trends call for an integration of even more protocols and algorithms in a handheld device. The clinical robustness and response quality of these new entries is yet to be evaluated.

### **8. Appendix**

emphasis on pure tone behavioral responses, tympanometry, and ABR [40]. The OAEs were found the less effective tool in the battery of screening tests, suffering mainly from the ambient

Recently, the fifth-generation OAE equipment appeared in the market. A number of OAE manufacturers (Natus, Path Medical solutions) proposed handheld devices capable of testing subjects with OAEs/AOAEs, AABR, and ASSR. A tympanometry assessment has not appeared so far due to complications in the probe of the device (canal pressurization issues). Mimosa Acoustics offers wide-reflectance measurements (which can substitute acoustic immittance)

The proposal from Path Medical Solutions (model: Sentiero—advanced) is a device capable not only of AOAE/AABR/ASSR protocols but also of protocols for speech Audiometry. The device is depicted in Figure 7. Such a device can be easily implemented in both phases (identification and intervention) of a UNHS program, and it is hoped that other manufacturers

**Figure 7.** The Sentiero Advanced device (data from the website of Path medical solutions http://www.pathme.de).

During the last 10–15 years, significant advances have been made toward the integration of various protocols and technologies in UNHS strategies. The most important contribution is in the area of auditory steady-state responses, which has been shown to be well correlated with other metrics in audiology such as the AABR, ABR, OAEs, and COR. The current technological trends call for an integration of even more protocols and algorithms in a handheld device. The

clinical robustness and response quality of these new entries is yet to be evaluated.

noise present in schools.

180 Update On Hearing Loss

**7. Conclusions**

and OAEs but not evoked potentials.

will follow this protocol-integration trend.

The reader interested in additional information than the one presented might visit the OAE Portal (http://www.otoemissions.org) and the OAE Portal Forum.

### **Author details**

Stavros Hatzopoulos1 , Henryk Skarzynski2 and Piotr H Skarzynski2,3,4

1 Department of Audiology and ENT, University of Ferrara, Italy

2 Institute of Physiology and Pathology of Hearing, Warsaw, Poland

3 Heart Failure and Cardiac Rehabilitation Department of the Medical University of War‐ saw, Poland

4 Institute of Sensory Organs, Kajetany, Poland

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