**3. Frequency following response: evaluation in infants**

In clinical practice, a comprehensive hearing evaluation for infants and young children is essential, since the integrity of their auditory system is the basis for acquiring oral language. In this context, if one measures only the functioning of the peripheral auditory pathway, perhaps by recording and analyzing otoacoustic emissions and/or auditory brainstem evoked potentials, it significantly constrains one's knowledge of the patient's hearing status. Moreover, behavioral assessments of hearing in very young children are often inconclusive, considering the diversity of neuropsychomotor development in this age group.

The perception of speech is important for the development of receptive and expressive language [13]. Through auditory experiences, infants and toddlers acquire and master the linguistic elements necessary for effective communication. The experiences are associated with information from the other senses, and together

**137**

*The Frequency Following Response: Evaluations in Different Age Groups*

pathway has implications for oral communication as a whole [14].

they allow the acquisition and development of oral language. Through listening, the subject understands oral language and creates concepts, finally inter-relating them and expressing them through speech [14]. Thus, the importance of hearing for the acquisition and development of language is vital, and any disturbance to the auditory

FFR testing can be used with infants and young children as a predictor of the extent of future language appropriation—in other words as a way of identifying children who are at risk of deficits in oral language acquisition [2, 15]. Assessment by FFR of infants and young children is relatively recent, and published studies of its potential have only been done over the last decade. Before discussing what is known about FFR in this population, it is first necessary to clarify an important

It is known that peripheral hearing is functional even before birth, whereas myelination and the organization of neural connections keep developing after birth [16, 17]. Indeed, the central structures, such as the subcortex and cortex, develop throughout the early years of human life. There is an ascending myelination of the auditory pathway, evidenced by magnetic resonance imaging. Up to the 13th week of life, there is an increase in myelination density of the cochlear nucleus, the superior olivary complex, and the lateral lemniscus, with the inferior colliculus demonstrating an increase in density around the 39th week of life [18]. This continuous process of myelination of the higher structures of the auditory pathway during the first year of life must be considered when evaluating the FFR, for it means that the lower the age of the evaluated subject, the greater the latency of the FFR waves [19, 20]. This increase in latency can also be seen in other auditory evoked potentials [21]. An FFR can be recorded from a neonate, but the responses only become readily apparent from the third month of age [15]. The existence of a series of FFR waves—V, A, C, D, E, F, and O—in neonates has been pointed out by several researchers [15, 19, 22–26]. FFR evaluations have been performed with the vowel /i/ [15, 24], the syllables /ba/ and /ga/ [26], and the syllable /da/ [23]. The FFR has been studied in neonates of different nationalities (Chinese, American) during the first days after birth, and the FFRs were nearly the same. This finding makes it possible to infer that, independent of the mother tongue, there is an innate capacity for speech coding in neonates at the subcortical level [22].

The evaluation of subcortical representation of speech coding was studied by evaluating FFRs in 28 healthy North American infants, 3–10 months of age. The study focused on the fundamental frequency (F0), the response time of the FFR, and the representation of harmonics. To analyze the data in the frequency domain, spectral amplitudes were calculated by fast Fourier transform (FFT) and divided into three frequency ranges: F0, 103–125 Hz; first formant (F1), 220–720 Hz; and high harmonics (HH), 720–1120 Hz. The F0 responses were more robust in infants 3 months of age and the amplitude of F0 did not show significant changes over the entire 6 months. For the F1 and HH frequencies, there was a rapid and systematic

To analyze the data in the time domain, the peaks were identified manually and confirmed by a second observer. Waves I, III, and V were first identified in response to a click, and then, in the FFR, the same peak and following valley (V and A), the peaks (D, E, and F), and the displacement peak (O). Non-detectable peaks were marked as missing data points and were excluded from analysis. The latencies and amplitudes (baseline to peak) were extracted from the identified waves. The time domain analysis demonstrated a decrease in neural conduction time and an improvement in amplitude with increasing age. The latencies of A and O, the time interval between A and O, and the slope between V and A were shown to have a negative correlation between latency and age. In addition, there was an improvement in the morphology

*DOI: http://dx.doi.org/10.5772/intechopen.85076*

factor: maturation of the auditory pathway.

increase of amplitude from 3 to 6 months of age.

#### *The Frequency Following Response: Evaluations in Different Age Groups DOI: http://dx.doi.org/10.5772/intechopen.85076*

*The Human Auditory System - Basic Features and Updates on Audiological Diagnosis and Therapy*

Acquisition of an FFR is very similar to collecting an ABR with a click stimulus. However, interpretation of an FFR requires that the audiologist has a more sophisticated knowledge base. Speech stimuli allow a more complex analysis of the

An FFR evaluation can be performed on different clinical populations and age groups, and below we give details of how the procedure varies depending on the patient's age. Because FFR is a relatively new procedure, initial work was done on adult subjects. Afterward, researchers turned their interest to the study of responses

In order for an FFR assessment to be useful in identifying auditory disorders at an early stage, normative values using different equipment and recording parameters need to be established and compared with language acquisition markers. The distinctive features of FFRs in different age groups will be presented in

In clinical practice, a comprehensive hearing evaluation for infants and young children is essential, since the integrity of their auditory system is the basis for acquiring oral language. In this context, if one measures only the functioning of the peripheral auditory pathway, perhaps by recording and analyzing otoacoustic emissions and/or auditory brainstem evoked potentials, it significantly constrains one's knowledge of the patient's hearing status. Moreover, behavioral assessments of hearing in very young children are often inconclusive, considering the diversity of

The perception of speech is important for the development of receptive and expressive language [13]. Through auditory experiences, infants and toddlers acquire and master the linguistic elements necessary for effective communication. The experiences are associated with information from the other senses, and together

in infants and young children, children and adolescents, and the elderly.

**2. Frequency following response**

• frequency content and magnitude;

• difference between individual responses.

• evaluation in children and adolescents;

neuropsychomotor development in this age group.

**3. Frequency following response: evaluation in infants**

• evaluation in adults and the elderly.

responses, such as their:

• frequency tracking;

• phase consistency;

• intrinsic factors; and

• evaluation in infants;

• timing;

three parts:

• magnitude;

**136**

they allow the acquisition and development of oral language. Through listening, the subject understands oral language and creates concepts, finally inter-relating them and expressing them through speech [14]. Thus, the importance of hearing for the acquisition and development of language is vital, and any disturbance to the auditory pathway has implications for oral communication as a whole [14].

FFR testing can be used with infants and young children as a predictor of the extent of future language appropriation—in other words as a way of identifying children who are at risk of deficits in oral language acquisition [2, 15]. Assessment by FFR of infants and young children is relatively recent, and published studies of its potential have only been done over the last decade. Before discussing what is known about FFR in this population, it is first necessary to clarify an important factor: maturation of the auditory pathway.

It is known that peripheral hearing is functional even before birth, whereas myelination and the organization of neural connections keep developing after birth [16, 17]. Indeed, the central structures, such as the subcortex and cortex, develop throughout the early years of human life. There is an ascending myelination of the auditory pathway, evidenced by magnetic resonance imaging. Up to the 13th week of life, there is an increase in myelination density of the cochlear nucleus, the superior olivary complex, and the lateral lemniscus, with the inferior colliculus demonstrating an increase in density around the 39th week of life [18]. This continuous process of myelination of the higher structures of the auditory pathway during the first year of life must be considered when evaluating the FFR, for it means that the lower the age of the evaluated subject, the greater the latency of the FFR waves [19, 20]. This increase in latency can also be seen in other auditory evoked potentials [21]. An FFR can be recorded from a neonate, but the responses only become readily apparent from the third month of age [15]. The existence of a series of FFR waves—V, A, C, D, E, F, and O—in neonates has been pointed out by several researchers [15, 19, 22–26]. FFR evaluations have been performed with the vowel /i/ [15, 24], the syllables /ba/ and /ga/ [26], and the syllable /da/ [23].

The FFR has been studied in neonates of different nationalities (Chinese, American) during the first days after birth, and the FFRs were nearly the same. This finding makes it possible to infer that, independent of the mother tongue, there is an innate capacity for speech coding in neonates at the subcortical level [22].

The evaluation of subcortical representation of speech coding was studied by evaluating FFRs in 28 healthy North American infants, 3–10 months of age. The study focused on the fundamental frequency (F0), the response time of the FFR, and the representation of harmonics. To analyze the data in the frequency domain, spectral amplitudes were calculated by fast Fourier transform (FFT) and divided into three frequency ranges: F0, 103–125 Hz; first formant (F1), 220–720 Hz; and high harmonics (HH), 720–1120 Hz. The F0 responses were more robust in infants 3 months of age and the amplitude of F0 did not show significant changes over the entire 6 months. For the F1 and HH frequencies, there was a rapid and systematic increase of amplitude from 3 to 6 months of age.

To analyze the data in the time domain, the peaks were identified manually and confirmed by a second observer. Waves I, III, and V were first identified in response to a click, and then, in the FFR, the same peak and following valley (V and A), the peaks (D, E, and F), and the displacement peak (O). Non-detectable peaks were marked as missing data points and were excluded from analysis. The latencies and amplitudes (baseline to peak) were extracted from the identified waves. The time domain analysis demonstrated a decrease in neural conduction time and an improvement in amplitude with increasing age. The latencies of A and O, the time interval between A and O, and the slope between V and A were shown to have a negative correlation between latency and age. In addition, there was an improvement in the morphology

of all waves as age increased. It was also observed that infants 3–5 months of age had longer latencies, smaller intervals between A and O, and a lower V/A slope compared to those 6–10 months of age. This negative correlation between the latencies and the age of the infants, as well as the decrease of slope in the smaller children, is due to a maturational process occurring in the subcortical auditory system and shows that there is less neural synchrony in younger infants [23]. The authors also note that these findings indicate that at approximately 6 months of age, the coding of speech characteristics, both spectrally and temporally, becomes more like those of an adult, although the changes continue through to school age. These findings indicate that FFR evaluation can detect early disorders in the perception of speech sounds.

The researchers also investigated the development of subcortical speech processing in Chinese infants born in households in which the mother tongue was Mandarin. They recorded FFRs at two ages: 1–3 days of life and at 3 months. This prospective-longitudinal design study included only infants who had undergone auditory screening at birth, who had no obvious neurological disorders, and did not have any risk indicator for hearing loss. Initially, 44 newborns were tested by FFR during natural sleep. After that, the sample was divided into groups. For each group, the researchers selected different speech stimuli for the evaluation of FFR (monosyllables contrasting with Mandarin). Only 13 infants completed the followup protocol at the third month. The processing and tracking of the fundamental frequencies of human speech at the subcortical level, evidenced by the FFR, showed more robust responses when the babies were 3 months old. Researchers acknowledged the limitations of the study, including statistical analysis and data interpretation. A research weakness was the relatively low completion rate (i.e., 17/44 infants or 38.64%). This factor undermined the power of the conclusions and prevented the possibility of performing statistical analyses for each Mandarin tone used. Despite the limitations of the study, the findings fill a gap in understanding the developmental trajectory of subcortical processing during the first 3 months of life [25].

From the theoretical assumptions highlighted in the previous reference, it should be noted that the linguistic environment of a newborn has a substantial effect on the development of its speech perception. Even at birth, children are able to detect subtle differences in verbal sounds. Newborns can effectively differentiate all the features of human speech and most infants who participated in an FFR follow-up showed improvement in pitch tracking and response amplitudes at 3 months of age [25]. Such neural refinements observed by FFR are often highlighted in the literature for both infants [22, 24] and young infants [15, 23]. For example, in a longitudinal case report of one infant, the researchers obtained FFR records when the infant was 1, 3, 5, 7, and 10 months old. The results showed an evolving trajectory of development with a transition point of about 3 months [15].

Using FFR evaluation in preterm infants may also be an alternative for the early diagnosis of auditory disorders in this population related to the perception of speech sounds. Premature babies are at high risk of developing language disorders, so using FFR may be a way of measuring immature neural activity and predicting possible changes in the processing of verbal sounds. In order to do so, one study evaluated 12 premature Indian infants through FFR with the aim of exploring how an immature auditory system responds to complex acoustic stimuli such as speech [27]. Peaks V, A, C, D, E, and F were detected in almost all babies and with latencies and amplitudes similar to those reported in the literature. The waves could be replicated. The authors conclude that FFR may be a way of understanding how the human brain-stem receives speech signals and that such an assessment might be important for all highrisk babies. Although the findings of this study cannot be generalized, mainly due to the limited data (small sample and absence of a controls, among others), they point out the potential of FFR in evaluating infants from neonatal intensive care units.

**139**

brain stem, and cortex.

3–5 years (**Tables 1** and **2**).

presented in **Table 3**.

recording [29].

*The Frequency Following Response: Evaluations in Different Age Groups*

More recently, studies that record FFRs in the presence of background noise have been published. It is known that competing noise can make speech comprehension more difficult in people of all ages. Speech-in-noise tests are clinically available but cannot be given to infants. Thus, the use of FFRs in noise may be an alternative for evaluating impaired speech perception in young children who are

In this context, with the objective of examining the electrophysiological responses in the presence of noise, researchers have evaluated the FFR in 30 children with typical development under conditions with and without noise (a signal-to-noise ratio of +10 dB in the former) [28]. Babies were divided into two age groups: 7–12 and 18–24 months. For all infants, frequency analysis of the FFR with a Fourier transform was performed, analyzing the latency and amplitude of waves V, A, D, E, and F, and correlation tests were carried out. In both groups, the mean latency of all recorded waves was higher in the presence of noise. According to the authors, this suggests that, at least for infants up to 24 months, the presence of noise causes a delay in the appearance of FFR waves independent of age. In addition, they observed a greater amplitude of F0 in the noise condition in the group of older babies; this difference was not seen in the silent condition. Thus, the authors point out that, at 2 years of age, infants are less vulnerable to the degrading effects of

The development of phase lock and frequency representation has also been evaluated in infants. This was the focus of a study that included an initial sample of 56 typical babies, aged between 2 and 12 months, and evaluated the FFR with / ba/ and /ga/ stimuli presented in the right ear using the SmartEP equipment from Intelligent Hearing Systems [26]. These responses were also obtained in young adults to provide a reference for the course of development of neural synchrony (represented by phase lock) and response amplitude (represented by spectral magnitude). The results obtained in this study demonstrate that the strength of phase-lock in the fine structure at CV transition is higher in young adults compared to infants. However, phase lock for F0 was equivalent between adults and infants. The frequency of F0 was found to be higher in older infants compared to younger infants and adults. Thus, these data demonstrate that speech coding can be evaluated in infants from 2 months of age and that such data are of value in a clinical setting, since it is known that performing electrophysiological evaluation of hearing in young children is difficult because they are less able to remain still during a test. The data indicate that the FFR may be a way of testing babies who are at risk of developing a language disorder, examining the auditory coding mainly of the midbrain, but also reflecting contributions from the auditory nerve,

The most commonly used parameters in FFR evaluations are: monoaural stimulus, right ear stimulation, intensity of 80 dB SPL, syllable /da/ speech stimulus, alternating polarity, presentation rate of 10.9 stimuli per second, vertical placement of electrodes, insert headphones, and the subject sitting distracted or awake during

Regarding the latency parameters, when FFR is done with the Navigator Pro AEP System (Natus Medical, Inc.) and a syllable stimulus, one group of researchers [19] pointed out that in 23 normal-hearing babies (0–12 months) the wave latencies were on average: V = 7.22 ms, A = 8.22 ms, D = 23.14 ms, E = 31.5 ms, F = 39.91 ms, and O = 49.64 ms. FFR wave latencies were also investigated in 53 children aged

Parameters of FFR evaluation in infants and young children used in the Hearing

Electrophysiology Service of the Federal University of Santa Maria, Brazil, are

*DOI: http://dx.doi.org/10.5772/intechopen.85076*

unable to respond to behavioral tests.

noise compared to children younger than 12 months.

*The Human Auditory System - Basic Features and Updates on Audiological Diagnosis and Therapy*

of all waves as age increased. It was also observed that infants 3–5 months of age had longer latencies, smaller intervals between A and O, and a lower V/A slope compared to those 6–10 months of age. This negative correlation between the latencies and the age of the infants, as well as the decrease of slope in the smaller children, is due to a maturational process occurring in the subcortical auditory system and shows that there is less neural synchrony in younger infants [23]. The authors also note that these findings indicate that at approximately 6 months of age, the coding of speech characteristics, both spectrally and temporally, becomes more like those of an adult, although the changes continue through to school age. These findings indicate that FFR evaluation can detect early disorders in the perception of speech sounds.

The researchers also investigated the development of subcortical speech processing in Chinese infants born in households in which the mother tongue was Mandarin. They recorded FFRs at two ages: 1–3 days of life and at 3 months. This prospective-longitudinal design study included only infants who had undergone auditory screening at birth, who had no obvious neurological disorders, and did not have any risk indicator for hearing loss. Initially, 44 newborns were tested by FFR during natural sleep. After that, the sample was divided into groups. For each group, the researchers selected different speech stimuli for the evaluation of FFR (monosyllables contrasting with Mandarin). Only 13 infants completed the followup protocol at the third month. The processing and tracking of the fundamental frequencies of human speech at the subcortical level, evidenced by the FFR, showed more robust responses when the babies were 3 months old. Researchers acknowledged the limitations of the study, including statistical analysis and data interpretation. A research weakness was the relatively low completion rate (i.e., 17/44 infants or 38.64%). This factor undermined the power of the conclusions and prevented the possibility of performing statistical analyses for each Mandarin tone used. Despite the limitations of the study, the findings fill a gap in understanding the developmental trajectory of subcortical processing during the first 3 months of life [25]. From the theoretical assumptions highlighted in the previous reference, it should be noted that the linguistic environment of a newborn has a substantial effect on the development of its speech perception. Even at birth, children are able to detect subtle differences in verbal sounds. Newborns can effectively differentiate all the features of human speech and most infants who participated in an FFR follow-up showed improvement in pitch tracking and response amplitudes at 3 months of age [25]. Such neural refinements observed by FFR are often highlighted in the literature for both infants [22, 24] and young infants [15, 23]. For example, in a longitudinal case report of one infant, the researchers obtained FFR records when the infant was 1, 3, 5, 7, and 10 months old. The results showed an evolving trajec-

tory of development with a transition point of about 3 months [15].

Using FFR evaluation in preterm infants may also be an alternative for the early diagnosis of auditory disorders in this population related to the perception of speech sounds. Premature babies are at high risk of developing language disorders, so using FFR may be a way of measuring immature neural activity and predicting possible changes in the processing of verbal sounds. In order to do so, one study evaluated 12 premature Indian infants through FFR with the aim of exploring how an immature auditory system responds to complex acoustic stimuli such as speech [27]. Peaks V, A, C, D, E, and F were detected in almost all babies and with latencies and amplitudes similar to those reported in the literature. The waves could be replicated. The authors conclude that FFR may be a way of understanding how the human brain-stem receives speech signals and that such an assessment might be important for all highrisk babies. Although the findings of this study cannot be generalized, mainly due to the limited data (small sample and absence of a controls, among others), they point out the potential of FFR in evaluating infants from neonatal intensive care units.

**138**

More recently, studies that record FFRs in the presence of background noise have been published. It is known that competing noise can make speech comprehension more difficult in people of all ages. Speech-in-noise tests are clinically available but cannot be given to infants. Thus, the use of FFRs in noise may be an alternative for evaluating impaired speech perception in young children who are unable to respond to behavioral tests.

In this context, with the objective of examining the electrophysiological responses in the presence of noise, researchers have evaluated the FFR in 30 children with typical development under conditions with and without noise (a signal-to-noise ratio of +10 dB in the former) [28]. Babies were divided into two age groups: 7–12 and 18–24 months. For all infants, frequency analysis of the FFR with a Fourier transform was performed, analyzing the latency and amplitude of waves V, A, D, E, and F, and correlation tests were carried out. In both groups, the mean latency of all recorded waves was higher in the presence of noise. According to the authors, this suggests that, at least for infants up to 24 months, the presence of noise causes a delay in the appearance of FFR waves independent of age. In addition, they observed a greater amplitude of F0 in the noise condition in the group of older babies; this difference was not seen in the silent condition. Thus, the authors point out that, at 2 years of age, infants are less vulnerable to the degrading effects of noise compared to children younger than 12 months.

The development of phase lock and frequency representation has also been evaluated in infants. This was the focus of a study that included an initial sample of 56 typical babies, aged between 2 and 12 months, and evaluated the FFR with / ba/ and /ga/ stimuli presented in the right ear using the SmartEP equipment from Intelligent Hearing Systems [26]. These responses were also obtained in young adults to provide a reference for the course of development of neural synchrony (represented by phase lock) and response amplitude (represented by spectral magnitude). The results obtained in this study demonstrate that the strength of phase-lock in the fine structure at CV transition is higher in young adults compared to infants. However, phase lock for F0 was equivalent between adults and infants. The frequency of F0 was found to be higher in older infants compared to younger infants and adults. Thus, these data demonstrate that speech coding can be evaluated in infants from 2 months of age and that such data are of value in a clinical setting, since it is known that performing electrophysiological evaluation of hearing in young children is difficult because they are less able to remain still during a test. The data indicate that the FFR may be a way of testing babies who are at risk of developing a language disorder, examining the auditory coding mainly of the midbrain, but also reflecting contributions from the auditory nerve, brain stem, and cortex.

The most commonly used parameters in FFR evaluations are: monoaural stimulus, right ear stimulation, intensity of 80 dB SPL, syllable /da/ speech stimulus, alternating polarity, presentation rate of 10.9 stimuli per second, vertical placement of electrodes, insert headphones, and the subject sitting distracted or awake during recording [29].

Regarding the latency parameters, when FFR is done with the Navigator Pro AEP System (Natus Medical, Inc.) and a syllable stimulus, one group of researchers [19] pointed out that in 23 normal-hearing babies (0–12 months) the wave latencies were on average: V = 7.22 ms, A = 8.22 ms, D = 23.14 ms, E = 31.5 ms, F = 39.91 ms, and O = 49.64 ms. FFR wave latencies were also investigated in 53 children aged 3–5 years (**Tables 1** and **2**).

Parameters of FFR evaluation in infants and young children used in the Hearing Electrophysiology Service of the Federal University of Santa Maria, Brazil, are presented in **Table 3**.


∑*: average (ms), SD: standard deviation, Detect: the percent detectability for each peak. Sample: 23 babies (0–1 years old).*

#### **Table 1.**

*FFR latency values using syllable /da/of 40-ms duration performed on babies with normal hearing (silent background) [19].*


∑*: average (ms), SD: standard deviation, Detect: the percent detectability for each peak. Sample: 53 children (3–5 years old).*

#### **Table 2.**

*FFR latency values using syllable /da/ of 40-ms duration performed in children with normal hearing (in silence) [19].*


**141**

**Table 6.**

*The Frequency Following Response: Evaluations in Different Age Groups*

V 6.61 0.25 0.31 0.15 A 7.51 0.34 0.65 0.19 C 17.69 0.48 0.36 0.09 F 39.73 0.61 0.43 0.19

*Sample: 36 and 38 children and adolescents (8–12 years old) with normal hearing.*

∑*: average, Med: median, SD: standard deviation, M: male, F: female.*

∑*: average, Med: median, SD: standard deviation, M: male, F: female.*

*Sample: 40 children and adolescents (8–16 years old).*

*children with normal hearing (silent conditions) [30].*

*Sample: 40 children and adolescents (8–16 years old).*

*with normal hearing (silent conditions) [30].*

**Source Latency (ms) Amplitude (μV) VA measures**

Slope VA (μV/ms) 0.13 0.05 Area VA (μV × ms) 1.70 1.23

*FFR latency and amplitude values using the syllable/da/of 40-ms duration, performed in children with normal* 

**Waves**

*FFR latency and amplitude values for males and females using syllable /da/ of 40-ms duration performed in children* 

**Sex Slope VA (ms/μV) Area VA (ms × μV)**

F 0.39 0.34

F 0.36 0.31

F 0.14 0.14

∑ M 0.31 0.29

Med M 0.29 0.31

SD M 0.11 0.09

**Complex VA**

**V A C D E F O Sex Lat Amp Lat Amp Lat Amp Lat Amp Lat Amp Lat Amp Lat Amp** ∑ M 6.53 0.10 7.53 0.19 18.43 0.08 22.29 0.17 30.86 0.21 39.31 0.17 48.02 0.13 F 6.49 0.13 7.43 0.23 18.33 0.12 22.28 0.15 30.81 0.29 39.27 0.24 47.95 0.21 Med M 6.49 0.10 7.53 0.18 18.28 0.07 22.24 0.09 30.86 0.21 39.28 0.7 48.11 0.13 F 6.49 0.12 7.37 0.22 18.37 0.09 22.11 0.13 30.78 0.22 39.11 0.24 47.86 0.21 SD M 0.19 0.05 0.32 0.04 0.44 0.05 0.32 0.07 0.53 0.07 0.44 0.08 0.45 0.07 F 0.22 0.07 0.35 0.90 0.44 0.11 0.67 0.09 0.58 0.35 0.56 0.26 0.75 0.28

**∑ SD ∑ SD ∑ SD**

The early identification of hearing disorders through FFR evaluation allows a speech-language pathologist to intervene, lessening the damage that this disorder can have on the development of speech skills in early childhood [2, 20, 22, 31]. This

*Complex VA (slope and area) values for males and females using syllable/da/of 40-ms duration performed in* 

*DOI: http://dx.doi.org/10.5772/intechopen.85076*

∑*: average, SD: standard deviation.*

*hearing on the right ear (silent conditions) [12].*

**Table 4.**

**Table 5.**

#### **Table 3.**

*Parameters of FFR in infants and young children.*


#### *The Frequency Following Response: Evaluations in Different Age Groups DOI: http://dx.doi.org/10.5772/intechopen.85076*

∑*: average, SD: standard deviation.*

*Sample: 36 and 38 children and adolescents (8–12 years old) with normal hearing.*

#### **Table 4.**

*The Human Auditory System - Basic Features and Updates on Audiological Diagnosis and Therapy*

**Waves**

∑ 7.22 8.22 23.14 31.51 39.91 49.64 SD 0.42 0.43 0.66 0.49 0.45 1.32 Detect (%) 86.9 86.96 91.30 91.30 82.61 65.22

**Waves**

∑ 6.59 7.56 22.36 30.90 39.34 48.14 SD 0.26 0.35 0.38 0.37 0.32 0.42 Detect 100 100 88.67 98.11 100 90.57

*FFR latency values using syllable /da/ of 40-ms duration performed in children with normal hearing (in silence) [19].*

Equipment SmartEP, Intelligent Hearing Systems (IHS)

Filter Low pass of 100 Hz and high pass of 2000 Hz

Low pass of 100 Hz and high pass of 3000 Hz

Electrodes Fz; Fpz; M1; M2 or Cz, M1, M2

**V A D E F O Lat Lat Lat Lat Lat Lat**

∑*: average (ms), SD: standard deviation, Detect: the percent detectability for each peak.*

∑*: average (ms), SD: standard deviation, Detect: the percent detectability for each peak.*

**Presentation parameters Setting**

Transducer Insert phones

Stimulation Right ear Stimulus Syllable /da/ Duration of stimulus 40 ms Presentation rate 10.9/s Window 80–100 ms

Polarity Alternating Intensity 80 dBnHL Number of stimuli 6000

Reproducibility 2 × 3000 stimuli Condition of evaluation Awake and quiet Impedance 3k Ohms

Artifact rejection Acceptance if <10%

*ms, millisecond; s, second; Hz, hertz; dB, decibel; HL, hearing level.*

*Parameters of FFR in infants and young children.*

*FFR latency values using syllable /da/of 40-ms duration performed on babies with normal hearing* 

*Sample: 23 babies (0–1 years old).*

*Sample: 53 children (3–5 years old).*

*(silent background) [19].*

**Table 1.**

**Table 2.**

**V A D E F O Lat Lat Lat Lat Lat Lat**

**140**

**Table 3.**

*FFR latency and amplitude values using the syllable/da/of 40-ms duration, performed in children with normal hearing on the right ear (silent conditions) [12].*


∑*: average, Med: median, SD: standard deviation, M: male, F: female. Sample: 40 children and adolescents (8–16 years old).*

#### **Table 5.**

*FFR latency and amplitude values for males and females using syllable /da/ of 40-ms duration performed in children with normal hearing (silent conditions) [30].*


∑*: average, Med: median, SD: standard deviation, M: male, F: female. Sample: 40 children and adolescents (8–16 years old).*

#### **Table 6.**

*Complex VA (slope and area) values for males and females using syllable/da/of 40-ms duration performed in children with normal hearing (silent conditions) [30].*

The early identification of hearing disorders through FFR evaluation allows a speech-language pathologist to intervene, lessening the damage that this disorder can have on the development of speech skills in early childhood [2, 20, 22, 31]. This


∑*: average, Med: median, SD: standard deviation, R: right, L: left. Sample: 40 children and adolescents (8–16 years old).*

### **Table 7.**

*FFR latency and amplitude values for right and left ears using syllable/da/of 40-ms duration performed on children with normal hearing (silent conditions) [30].*


∑*: average, Med: median, SD: standard deviation, R: right, L: left. Sample: 40 children and adolescents (8–16 years old).*

#### **Table 8.**

*Complex VA (slope and area) values for right and left ears using syllable/da/of 40 ms duration performed on children with normal hearing (silent conditions) [30].*


∑*: average, Med: median, SD: standard deviation, R: right, L: left. Sample: 40 children and adolescents (8–16 years old).*

#### **Table 9.**

*FFR latency and amplitude values for various age ranges using syllable/da/of 40-ms duration performed on children with normal hearing (silent conditions) [30].*

**143**

*The Frequency Following Response: Evaluations in Different Age Groups*

which time hearing abilities become more complex and elaborate.

• timing—via analysis of the onset and offset portions;

• pitch—by analysis of the fundamental frequency (F0);

Simplistically, it can be said that the FFR helps in understanding which speech sounds were spoken (their timing and harmonic cues) and who said it (pitch cues) [36]. In addition, an FFR test can be performed under two conditions: (i) in silence (presentation of verbal stimuli only), and (ii) in noise (presentation of verbal

In children and adolescents, studies have shown that FFRs change in latency as age increases. FFRs of children aged around 5 years appear to be very similar to the responses of children aged 8–12. However, the FFR pattern of children under 5 years has a somewhat different morphology and latency. According to Johnson et al. [33], the differences in children younger than 3 years are more evident in the initial portion of the responses (the onset), while in older children the change is more evident

• timbre—from analysis of the harmonics of F0.

stimuli plus background noise).

in the final portion (the offset) [3, 37].

assertion can be understood by appreciating the relationship between language development and the presence of stimulating auditory experiences in the first few

Future studies evaluating FFRs in infants will no doubt benefit from interdisciplinary collaboration which seeks to deepen understanding of the underlying mechanisms involved in the typical and atypical development of the auditory

**4. Frequency following response: evaluation in children and adolescents**

Because of the close relationship between hearing, language, and learning, it is extremely important to monitor hearing over the course of life. Especially in children, be it pre-school or school age, the aim should be to monitor auditory function, either through behavioral or electrophysiological assessments. The ideal would be a combination of both behavioral and electrophysiological methods, so that with numerous evaluations there are crosschecks which allow a more accurate diagnosis to be made. The electrophysiological procedure traditionally used in clinical practice is the click ABR. However, in evaluating children with language deficits, this type of sound stimulus is not ideal for making diagnoses. Assessments using verbal sound stimuli, such as used in FFR, appear to be more effective and reliable in cases of learning problems or school difficulties [6]. Evaluation via an FFR allows a detailed analysis of how verbal stimuli are encoded in the central auditory nervous system to be done. The FFR allows fine-grained auditory processing deficits associated with realworld communication skills to be identified. As well as being used for the early identification of auditory processing, it can also be used to assess hearing across different clinical populations [33, 34]. This electrophysiological procedure can provide reliable and objective information about acoustic patterns such as timing, pitch, and timbre [35]. These three elements can be evaluated using different parts of the FFR, as follows:

Auditory impairment is almost invariably associated with language and communication deficits. Learning a spoken language depends on assimilating the acoustic and phonetic elements of a language [32]. The development of the central auditory nervous system begins in intrauterine life and continues until adolescence, over

*DOI: http://dx.doi.org/10.5772/intechopen.85076*

system during early childhood.

months of life.

*The Human Auditory System - Basic Features and Updates on Audiological Diagnosis and Therapy*

**Waves**

*FFR latency and amplitude values for right and left ears using syllable/da/of 40-ms duration performed on* 

∑ R 0.37 0.33

Med R 0.32 0.31

SD R 0.14 0.13

**Complex VA**

L 0.34 0.31

L 0.32 0.31

L 0.13 0.13

*Complex VA (slope and area) values for right and left ears using syllable/da/of 40 ms duration performed on* 

**Waves**

∑ 8–11 6.53 0.12 7.44 0.22 18.37 0.11 22.26 0.15 30.80 0.25 39.34 0.21 47.95 0.17 12–16 6.46 0.11 7.51 0.21 18.36 0.10 22.32 0.10 30.89 0.28 39.19 0.21 48.02 0.21 Med 8–11 6.53 0.11 7.45 0.21 18.37 0.09 22.20 0.14 30.78 0.23 39.28 0.20 47.95 0.15 12–16 6.45 0.12 7.45 0.17 18.28 0.08 22.20 0.09 30.86 0.20 39.11 0.15 48.03 0.13 SD 8–11 0.23 0.06 0.32 0.10 0.46 0.09 0.53 0.08 0.62 0.19 0.56 0.11 0.75 0.14 12–16 0.17 0.06 0.37 0.07 0.41 0.08 0.63 0.45 0.43 0.22 0.42 0.32 0.46 0.33

*FFR latency and amplitude values for various age ranges using syllable/da/of 40-ms duration performed on* 

**V A C D E F O**

**Lat Amp Lat Amp Lat Amp Lat Amp Lat Amp Lat Amp Lat Amp**

**Ear Slope VA (ms/μV) Area VA (ms × μV)**

∑*: average, Med: median, SD: standard deviation, R: right, L: left.*

∑*: average, Med: median, SD: standard deviation, R: right, L: left.*

∑*: average, Med: median, SD: standard deviation, R: right, L: left.*

*Sample: 40 children and adolescents (8–16 years old).*

*children with normal hearing (silent conditions) [30].*

*Sample: 40 children and adolescents (8–16 years old).*

*children with normal hearing (silent conditions) [30].*

*Sample: 40 children and adolescents (8–16 years old).*

*children with normal hearing (silent conditions) [30].*

**Table 7.**

**Table 8.**

**Age range** **V A C D E F O**

**Ear Lat Amp Lat Amp Lat Amp Lat Amp Lat Amp Lat Amp Lat Amp** ∑ R 6.50 0.12 7.46 0.22 18.33 0.10 22.21 0.14 30.89 0.30 39.37 0.24 48.00 0.21 L 6.51 0.11 7.48 0.21 18.41 0.11 22.36 0.13 30.78 0.23 39.20 0.19 47.95 0.16 Med R 6.45 0.12 7.45 0.21 18.33 0.08 22.12 0.14 30.86 0.23 39.24 0.19 47.99 0.15 L 6.53 0.11 7.41 0.21 18.33 0.09 22.28 0.11 30.78 0.21 39.07 0.18 48.03 0.15 SD R 0.21 0.06 0.33 0.09 0.42 0.08 0.66 0.09 0.50 0.39 0.55 0.29 0.75 0.30 L 0.21 0.06 0.36 0.07 0.46 0.10 0.44 0.08 0.61 0.09 0.47 0.09 0.54 0.12

**142**

**Table 9.**

assertion can be understood by appreciating the relationship between language development and the presence of stimulating auditory experiences in the first few months of life.

Future studies evaluating FFRs in infants will no doubt benefit from interdisciplinary collaboration which seeks to deepen understanding of the underlying mechanisms involved in the typical and atypical development of the auditory system during early childhood.
