*2.3.1 Brainwave analysis method*

After the fast Fourier transform (FFT) was applied to the brainwaves, ACF of CBW calculations were performed for the α-waves (8–13 Hz) and β-waves (13–30 Hz) of the left and right hemispheres. In the earlier study by Chen and Ando [15], 100 Hz α-waves and 500 Hz β-waves were sampled according to the sampling frequency laws and, after A/D conversion (16 bits), input into a computer to calculate the effective duration (*τe*) of CBWs' ACF (**Figure 4**). In ACF calculations of *τe* values in the study by Chen and Chan [16], the 0.3 s integration time (2 *T*) of monosyllabic speech sounds was suggested to be the most effective. Eventually, the monosyllabic signals were played in this study included simulation of the first delay time [17]. Therefore, the integration time (2 *T*) of ACF of continuous brainwaves (CBW) used in calculation was adjusted to 0.5 s. As shown in **Figure 4**, substantial differences were observed in the ACF waveforms of α-waves and β-waves under the same first delay time settings.

**39**

*sound by A0, A1 and A2.*

**Table 3.**

**Figure 2.**

*The Influence on Cortical Brainwaves in Relation to Word Intelligibility and ASW in Room*

To explore the changes in subjective perceptions of ASW, AEPs of nine participants were induced, recorded and analyzed as in the psychological intelligibility experiment. However, a spatial impression of a sound signal is a short-term memory phenomenon. Therefore, waveforms induced by the brain AEPs are normally used to observe changes in responses to weak brainwave signals (about 10–100 μV in

*The parameters of subjective source apparent width (ASW) test arranged by 2 kHz pure tone burst.*

*Note: I-1, I-2 and I-3 denote the sound intensity of direct sound and 1st and 2nd reflections sound measured at the location of the head top of the participants. a denotes the amplitude of the direct sound, 1st reflective and 2nd reflective* 

*The percentage syllabic articulation of monosyllable functioning initial time delay of a sound field.*

0.35 1 62.6 0.8 0.57 1 62.6 0.8 0.68 1 55.4 0.4 0.81 1 64.0 0.2

59.4 0.8 59.4 65 59.4 0.8 59.4 65 53.4 0.4 55.4 65 53.4 0.2 53.4 65

**reflection (A2)**

**I-2, SPL/dB(A) Amplitude of second** 

**IACCE3 (setup values) Amplitude of direct sound (A0) I-1, SPL/dB(A) Amplitude of first reflection (A1)**

**I-3, SPL/dB(A) Σ***L* **Total SPL dB(A)**

*DOI: http://dx.doi.org/10.5772/intechopen.85044*

*The Influence on Cortical Brainwaves in Relation to Word Intelligibility and ASW in Room DOI: http://dx.doi.org/10.5772/intechopen.85044*

**Figure 2.** *The percentage syllabic articulation of monosyllable functioning initial time delay of a sound field.*


*Note: I-1, I-2 and I-3 denote the sound intensity of direct sound and 1st and 2nd reflections sound measured at the location of the head top of the participants. a denotes the amplitude of the direct sound, 1st reflective and 2nd reflective sound by A0, A1 and A2.*

#### **Table 3.**

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

immediately determine and record the relative probability of ASWs. Each questionnaire was conducted for 1 min. The psychological scale values of ASWs are shown in **Figure 3** calculated using Thurstone's Case V [11]. Non-linear correlation was

After the fast Fourier transform (FFT) was applied to the brainwaves, ACF of CBW calculations were performed for the α-waves (8–13 Hz) and β-waves (13–30 Hz) of the left and right hemispheres. In the earlier study by Chen and Ando [15], 100 Hz α-waves and 500 Hz β-waves were sampled according to the sampling frequency laws and, after A/D conversion (16 bits), input into a computer to calculate the effective duration (*τe*) of CBWs' ACF (**Figure 4**). In ACF calculations of *τe* values in the study by Chen and Chan [16], the 0.3 s integration time (2 *T*) of monosyllabic speech sounds was suggested to be the most effective. Eventually, the monosyllabic signals were played in this study included simulation of the first delay time [17]. Therefore, the integration time (2 *T*) of ACF of continuous brainwaves (CBW) used in calculation was adjusted to 0.5 s. As shown in **Figure 4**, substantial differences were observed in the ACF waveforms of α-waves and β-waves under the same first delay time settings.

observed in the IACCE3 result [14].

*2.3.1 Brainwave analysis method*

**2.3 Brainwave physiological experiment methods**

*The setup of the instrumental diagram (audio arrangement and EEG recordings).*

*The setting of the physical parameters in subjective articulation test of monosyllables.*

Δ*t*1 (ms) Delay gap: 0 ms, 35 ms, 100 ms, 150 ms, 200 ms SPL of individual loudspeakers Direct sound: 60 dB(A); first reflection, Δ*t*1: 55 dB(A)

**Item Conditions of experiments**

Reverberation times *RT* ≑ 0.1 s

**38**

**Figure 1.**

**Table 2.**

*The parameters of subjective source apparent width (ASW) test arranged by 2 kHz pure tone burst.*

To explore the changes in subjective perceptions of ASW, AEPs of nine participants were induced, recorded and analyzed as in the psychological intelligibility experiment. However, a spatial impression of a sound signal is a short-term memory phenomenon. Therefore, waveforms induced by the brain AEPs are normally used to observe changes in responses to weak brainwave signals (about 10–100 μV in

**Figure 3.** *The scale values of subjective ASW test functioning IACCE3.*

#### **Figure 4.**

*The ACF curve of α-wave (left) and β-wave (right) recorded in relation to the monosyllable "tzuen1" were announcing.*

amplitude when measured from the scalp). Clear consistent brain waveforms are usually obtained by applying the signal averaging method [18] to responses that occur within 500 ms after auditory stimulation (**Figure 5**). In this study, 180 times of averaging process was applied here since the wave form of slow vertex responses (SVR) were clearly obtained. The movements (latency) of waveform peaks and troughs in the wave relative amplitude can reflect the activation of different parts of auditory nerves [19, 20]. As shown in **Figure 5**, this study changed ASW perceptions by changing the sound arrival orientation and energy while fixed reflection delay and echo times (Δ*t*1 < 15.5 ms, *RT* ≑ 0.1 s) (**Table 3**). This study suggested that brain waveforms could be observed using SVR because the preset reaction time exceeded 10 ms. In such way, AEPs were obtained. Consequently, when potentials P1, P2, N1, and N2 of posterior waveforms (30–200 ms) among different AEPs were generated by different sound stimulus, the relative amplitudes of P1-N1 and P2-N2, and P1, P2, N1, and N2 latency were observed [18].

### *2.3.2 Brainwave recording method*

With regard to brainwave recording, eight participants (and other nine in the AEPs experiments) sat on comfortable office chairs in the semi-anechoic room at Chaoyang University of Technology and their brainwaves were induced and

**41**

the recordings.

and questionnaires.

**Figure 5.**

*Ichikawa [17].*

*The Influence on Cortical Brainwaves in Relation to Word Intelligibility and ASW in Room*

recorded. The room temperature was maintained at 22 ± 2°C. All subjects were prohibited from drinking any alcohol for a period of 3 days before the brainwave recordings were conducted, and they refrained from smoking for 1 h before both experiments. They were instructed to concentrate on listening to the signals during the presentation. The participating subjects were eight male students (plus another nine male students in the AEPs experiments) aged 22–24 years old with normal hearing ability, as confirmed by an audiometry test and right-handed test (self-administered). The audiometry test detects sensorineural hearing loss (damage to the nerve or cochlea) and conductive hearing loss (damage to the eardrum or the tiny ossicle bones). Pure-tone subjective audiometry, in which air conduction hearing thresholds in decibels (dB) for a frequency range of 250–8000 Hz are plotted on an audiogram for each ear independently, was applied. All of the subjects had to be qualified as normal with a pure-tone audiogram (less than 25 dB) for both ears prior to the brainwave experiments

*The diagram illustrates brain waves in different time domains and their index at the peak or trough by* 

This procedure has been applied in many studies, such as those by Chen et al.

Electrodes used to explore brainwaves were positioned at the participants' T3 and T4 head points according to the international 10–20 system [21]. Electric potentials were examined using eardrops on the left and right sides. Unipolar induction of continuous brainwaves in the left and right hemispheres was performed. The G2 electrode was attached between the eyebrows for eye movement reference. The electrode system was grounded each time the brainwaves were recorded in order to avoid external electric interference. The settings of the simulated sound field were similar to that in the aforementioned psychological experiment [16]. The collected brainwave data was analyzed and processed by NI LabVIEW software. The setup of the instrumental diagram is shown in **Figure 1**. During the brainwave experiments, the subjects had to be relaxed while paying close attention to the sound stimuli. Brainwaves are extremely sensitive to any incoming stimuli or stress. For the purpose of this study, a relaxed state but one also focused on environmental variations was considered the best condition for the subjects during the brainwave recording process. For the recordings, periods of blinking had to be disregarded. Thus, a monitor was set up in the anechoic chamber to identify these periods, and these sections were later removed from

[9], Ando et al. [19], and Ando et al. [20], among others.

*DOI: http://dx.doi.org/10.5772/intechopen.85044*

*The Influence on Cortical Brainwaves in Relation to Word Intelligibility and ASW in Room DOI: http://dx.doi.org/10.5772/intechopen.85044*

#### **Figure 5.**

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

amplitude when measured from the scalp). Clear consistent brain waveforms are usually obtained by applying the signal averaging method [18] to responses that occur within 500 ms after auditory stimulation (**Figure 5**). In this study, 180 times of averaging process was applied here since the wave form of slow vertex responses (SVR) were clearly obtained. The movements (latency) of waveform peaks and troughs in the wave relative amplitude can reflect the activation of different parts of auditory nerves [19, 20]. As shown in **Figure 5**, this study changed ASW perceptions by changing the sound arrival orientation and energy while fixed reflection delay and echo times (Δ*t*1 < 15.5 ms, *RT* ≑ 0.1 s) (**Table 3**). This study suggested that brain waveforms could be observed using SVR because the preset reaction time exceeded 10 ms. In such way, AEPs were obtained. Consequently, when potentials P1, P2, N1, and N2 of posterior waveforms (30–200 ms) among different AEPs were generated by different sound stimulus, the relative amplitudes of P1-N1 and P2-N2, and P1, P2,

*The ACF curve of α-wave (left) and β-wave (right) recorded in relation to the monosyllable "tzuen1" were* 

With regard to brainwave recording, eight participants (and other nine in the AEPs experiments) sat on comfortable office chairs in the semi-anechoic room at Chaoyang University of Technology and their brainwaves were induced and

**40**

**Figure 3.**

**Figure 4.**

*announcing.*

*The scale values of subjective ASW test functioning IACCE3.*

N1, and N2 latency were observed [18].

*2.3.2 Brainwave recording method*

*The diagram illustrates brain waves in different time domains and their index at the peak or trough by Ichikawa [17].*

recorded. The room temperature was maintained at 22 ± 2°C. All subjects were prohibited from drinking any alcohol for a period of 3 days before the brainwave recordings were conducted, and they refrained from smoking for 1 h before both experiments. They were instructed to concentrate on listening to the signals during the presentation. The participating subjects were eight male students (plus another nine male students in the AEPs experiments) aged 22–24 years old with normal hearing ability, as confirmed by an audiometry test and right-handed test (self-administered). The audiometry test detects sensorineural hearing loss (damage to the nerve or cochlea) and conductive hearing loss (damage to the eardrum or the tiny ossicle bones). Pure-tone subjective audiometry, in which air conduction hearing thresholds in decibels (dB) for a frequency range of 250–8000 Hz are plotted on an audiogram for each ear independently, was applied. All of the subjects had to be qualified as normal with a pure-tone audiogram (less than 25 dB) for both ears prior to the brainwave experiments and questionnaires.

This procedure has been applied in many studies, such as those by Chen et al. [9], Ando et al. [19], and Ando et al. [20], among others.

Electrodes used to explore brainwaves were positioned at the participants' T3 and T4 head points according to the international 10–20 system [21]. Electric potentials were examined using eardrops on the left and right sides. Unipolar induction of continuous brainwaves in the left and right hemispheres was performed. The G2 electrode was attached between the eyebrows for eye movement reference. The electrode system was grounded each time the brainwaves were recorded in order to avoid external electric interference. The settings of the simulated sound field were similar to that in the aforementioned psychological experiment [16]. The collected brainwave data was analyzed and processed by NI LabVIEW software. The setup of the instrumental diagram is shown in **Figure 1**. During the brainwave experiments, the subjects had to be relaxed while paying close attention to the sound stimuli. Brainwaves are extremely sensitive to any incoming stimuli or stress. For the purpose of this study, a relaxed state but one also focused on environmental variations was considered the best condition for the subjects during the brainwave recording process. For the recordings, periods of blinking had to be disregarded. Thus, a monitor was set up in the anechoic chamber to identify these periods, and these sections were later removed from the recordings.
