A Potential Objective Measurement for Binaural Fitting
Frequency Following Response to Interaural Phase Changes – A Potential Objective Measurement for Binaural Fitting Jaime A. Undurraga, Nicholas R. Haywood, Torsten Marquardt & David McAlpine UCL Ear Institute, University College London, 332 Gray’s Inn Rd., London WC1X8EE
AF 7
F7
FT 7
LE
T9
T7
T P7
P9
F5
AF 3
FP 2
F3
F1
FZ
AF 8
AF 4
AF Z
F4
F2
F8
F6
FC 5
FC 3
FC 1
FC Z
FC 2
FC 4
FC 6
C5
C3
C1
CZ
C2
C4
C6
CP 5
CP 3
CP 1
CP Z
CP 2
CP 4
CP 6
P7
P5
PO7
P1
P3
PO3
O1
PZ
POZ
OZ
P2
P4
PO4
P6
P8
FT 8
T8
T 10
13.7 Hz -45 ° +45 ° IPD Excursion 90°
The carrier was amplitude modulated using several rates (between 27 Hz and 109 Hz; IPD held at ±45◦). Example IPM-FRs from a single subject (Fig. 3) 1500
1500
SB:NH/Ch:t8 LE/Fc:520/Fm:41/Pc:33.8/Fj:1.7 RE/Fc:520/Fm:41/Pc:−33.8/Fj:1.7
PO8
O2
1500
SB:AR/Ch:t8 LE/Fc:520/Fm:41/Pc:33.8/Fj:3.4 RE/Fc:520/Fm:41/Pc:−33.8/Fj:3.4
1000
nV
1000
500
0
500
0 0
10
20 30 40 Frequency [Hz]
50
60
SB:AR/Ch:t8 LE/Fc:520/Fm:41/Pc:33.8/Fj:6.8 RE/Fc:520/Fm:41/Pc:−33.8/Fj:6.8
0.50 0.25
10
20 30 40 Frequency [Hz]
50
60
0
10
20 30 40 Frequency [Hz]
50
60
Simuli Experiment 2: Transposed tones at 2000 Hz, 3000 Hz and 4000 Hz (see Fig. 5). Temporal rate was 128 pps. IPMs (6.8 Hz) imposed on the transposed pulses were amplitude modulated at 41.0 Hz. IPD were ±90◦ or 0◦/180◦ (transposed phase of 90◦ at one and −90◦ at the opposite ear). 0.2 (a)
13.7 Hz
1.5 1.0 0.5 0.0 −0.5 −1.0 −1.5 0
0.00 6.8 Hz Amplitude (µV)
0.75 0.50 0.25 0.00
13.7 Hz
0.75
0.25 0.00 0
13.7 Hz
1.5 1.0 0.5 0.0 −0.5 −1.0 −1.5
0.50
0.1 0.2 0.3 0.4 0.5 Time (ms)
6.8 Hz
1.5 1.0 0.5 0.0 −0.5 −1.0 −1.5
10 20 30 Frequency (Hz)
40
0
0.75
6.8 Hz
500 600
0.50
0.00 0.75
13.7 Hz
0.50 0.25
0.1 0.2 0.3 0.4 0.5 Time (ms)
(b)
(c)
0.00 0
10 20 30 Frequency (Hz)
40
(a) Dichotic IPM-FRs (b) Diotic controls Figure 6: Average responses across subjects. Time and frequency responses for both 6a dichotic and 6b diotic controls are shown, respectively. The IPM rate is indicated above each panel.
IPM-FRs to several IPDs and IPM rates (see Fig. 7a). Non-parametric repeated measures analysis of variance (ANOVA) with factors Electrode Position (left/right mastoid), IPM rate, and IPD: IPM rate (p < 0.001) IPD (p < 0.001) IPM rate * IPD (p = 0.014) IPM-FRs to a fixed IPD and several modulation and IPM rates (see Fig. 7b). Non-parametric repeated measures ANOVA with factors Electrode Position (left/right mastoid), IPM rate, and modulation rate: IPM rate (p < 0.001) Modulation rate (p = 0.002) (ratio between lowest and highest IPM-FR was 1.8) Electrode position (p = 0.001) (right 8 % > left hemisphere) IPM rate * carrier amplitude modulation rate (p = 0.016)
IPM rate
IPM rate
0 −0.1
3.4
Stimuli Experiment 1: Carrier phases were symmetrically opposed in each ear in order to create IPDs that ranged between 11◦ and 135◦ (see Fig. 3).
6.8
6.8
13.7
13.7
(e)
0.14 0.15 Time [s]
0.16
0.17
(f)
0.13
0.14 0.15 Time [s]
0.16
0.17
(g)
0.13
0.14 0.15 Time [s]
0.16
0.17
(h)
Magnitude
0.03 0.02
Amplitude [nV]
0.04
0.13
Amplitude [nV]
−0.2 0.17
500
500
250
250
0
0
0.01 0
0
2000 4000 Frequency [Hz]
60000
2000 4000 Frequency [Hz]
60000
200
3000
3250
3500 3750 Carrier Rate [Hz]
4000
-1000
-500 0 500 Across ear carrier offset [Hz]
1000
(a) Matched cochlear regions (Figs. 5 (a),(e) and (b),(f) (b) Mismatched cochlear regions (Figs. 5(c),(g) and (d),(h)) Figure 8: IPM-FRs with transposed stimuli
Conclusions IPM-FRs could be reliably obtained. The SNR was largest for IPMs rates of 6.8 Hz and for IPDs between ±45◦ and ±90◦ at lower frequency regions. The IPM-FR may be more suitable than ABR based BIC as an objective measure of binaural processing.
Acknowledgments
References
3.4
750
IZ
0.16
200
300
(d)
750
0.14 0.15 Time [s]
400
400
IPD ± 90 0 / 180
The research leading to these results has received funding from the European Union’s Seventh Framework Programme (FP7/2007-2013) under ABCIT grant agreement number 304912.
0.1
0.13
IPD ± 90 0 / 180
0.25
0 0
(a) Example IPM-FR at 3.4 Hz IPM rate (b) Example IPM-FR at 6.8 Hz IPM rate (c) Example IPM-FR at 13.6 Hz IPM rate Figure 4: Examples IPM-FRs at different IPM rates. Significant responses (see Eq. 1) are shown by coloured markers.
RE
6.8 Hz
1.5 1.0 0.5 0.0 −0.5 −1.0 −1.5
3.4 Hz
Results of this pilot experiment demonstrated that IPM-FR could also be obtained at basal regions of the cochlea. Increasing carrier rates resulted in reduced response amplitude. Responses were significantly larger for the 0◦ to 180◦ condition than for the ±90◦ condition, suggesting than binaural processing relies on different mechanisms at basal sites of the cochlea. Responses obtained at different carrier rate offsets between ears agree with the hypothesis that interaural processing decreases when there is an across ear frequency mismatch.
Spectral magnitude [nV]
6.8 Hz -45 ° +45 ° IPD Excursion 90°
Figure 3: Stimuli used to elicit IPM-FRs. Top -45 ° +45 ° IPD panel: zoomed stimuli presented at the right Excursion (black) and left (gray) ear, respectively. 90° Bottom panel: same as top, in a large scale. Figure 2: Illustration of intracranial IPMs. Overtime, IPMs The leading phase is indicated by the color. produce moving intracranial transitions able to elicit IPM-FRs Different IPM rates present a large number of (real examples in Fig. 4). IPD transitions.
T P8
P 10
0.25
0.75
Spectral Magnitude (µV)
3.4 Hz
Amplitude
FP Z
FP 1
3.4 Hz
1.5 1.0 0.5 0.0 −0.5 −1.0 −1.5
0.50
Time
nV
Recordings and Data Analyses Recordings: Low-impedance headstage (20x gain). Unitary preamplifier. Fs: 25 kHz / 16 bits. Bandpass: 2.2 Hz and 7.5 kHz. Impedances < 5 kΩ. Data Analyses: Figure 1: Recording electrodes Epochs -> FFT of 100000 points (0.24 Hz of resolution). Frequency bins of interest were selected from each epoch. Significance -> two-dimensional repeated measurement Hotelling’s T 2 test (Picton et al., 2003). T 2 = N [¯ x , y¯ ]⊺ S −1 [¯ x , y¯ ] (1) Multiplying T 2 by (N − 2) / (2N − 2) produces an F distributed value with 2 and N − 2 degrees of freedom.
3.4 Hz
0.75
Spectral Magnitude (µV)
Time
500
Subjects Fourteen (ten took part in experiment 1 and four in experiment 2) NH listeners (hearing thresholds were below 20 dB normal Hearing Level (HL) for pure tones between 250 Hz and 8000 Hz). Research ethics was approved by UCL research ethics committee and all participants provided their informed consent prior the beginning of the experiments.
3.4 Hz
1.5 1.0 0.5 0.0 −0.5 −1.0 −1.5
0.00
Time
1000
Methods
Results - Experiment 2
IPM-FRs to several IPDs and IPM rates. Figure 6 shows time and frequency responses obtained with low rate sinusoidal carriers (see Fig. 3) for both dichotic and diotic controls.
IPMs were presented at 3.4 Hz, 6.8 Hz and 13.6 Hz. Since IPMs resulted in IPD fluctuations of opposite sign we will further refer to them as ± IPD. It must be noted that the IPD excursion is twice this value, i.e. if the IPD was modulated from 45◦ to −45◦ (±45◦), the overall IPD extrusion was 90◦ (see Fig. 2).
Amplitude (µV)
Bilateral cochlear implants (CIs) provide the opportunity for implant users to access binaural cues, potentially increasing performance in spatial listening tasks. However, since implants are inserted and fitted independently, users may have place-mismatched electrode arrays, effectively exciting the same cochlear sites across-ears with information from different frequency channels. The measurement of binaural processing has been a challenge for many years. The most common approach consists of a set of measurements where monaural auditory brainstem responses (ABRs) are summed and subtracted from a binaural ABR. This difference is believed to correspond to a measurement of binaural processing (e.g Levine, 1981; Riedel and Kollmeier, 2002a,b). However, this measurement has several disadvantages: it is an indirect measurement of binaural processing, the response is small and has a poor Signal-to-Noise Ratio (SNR). Alternatively, more direct objective measurements have been proposed. Dajani and Picton (2006) measured steady-state responses to noise signals where interaural correlations varied between 1 and 0 at a fixed rate. Similarly, Ross et al. (2007) and Ross (2008) used Magnetoencephalography (MEG) to record evoked cortical responses to binaural amplitude modulated sinusoidal stimuli containing abrupt interaural phase changes (IPCs) at a fixed rate of 0.5 Hz. The present study focused on the detection of binaural responses by means of interaural phase modulation following response (IPM-FR), by using a similar approach to Ross (2008). In a first experiment, we investigated the effect of interaural phase modulation (IPM) rate, interaural phase difference (IPD), and modulation frequency through electroencephography (EEG) recordings in Normal Hearing (NH) listeners at a low carrier rate (apical region of the cochlea). A second experiment investigated IPM-FRs by means of transposed tones. Transposed tones allowed us to simulate mismatched electrodes in the basal region of the cochlea since the envelope shape could be controlled independently of the carrier frequency.
Results - Experiment 1
Spectral magnitude [nV]
Methods
nV
Introduction
2000 4000 Frequency [Hz]
60000
2000 4000 Frequency [Hz]
6000
Figure 5: Transposed stimuli. (a) and (b) illustrate diotic carriers for ±90◦ and 0◦/180◦ IPD conditions, respectively. (c) and (d) illustrate time domain waveforms for dichotic carriers for ±90◦ and 0◦/180◦ IPD conditions (note that envelopes are identical for dichotic and diotic carriers). (e) to (h) Spectra of (a) to (b) responses, respectively. Note that for (e) and (f) left (blue) and right (red) spectra overlap.
± 11.3
± 22.5
± 45
± 67.5 IPD
± 90
± 112.5
± 135
27.3
41 54.7 68.4 82 95.7 Carrier amplitude modulation rate [Hz]
109.4
(a) IPM-FR as a function of the IPD (b) IPM-FR as a function of the modulation rate Figure 7: IPM-FRs as a function of both 7a IPD and 7b for all IPM rates (color coded).
Dajani, H. R. and Picton, T. W. (2006). “Human auditory steady-state responses to changes in interaural correlation.” Hearing research 219, pp. 85–100. Levine, R. a. (1981). “Binaural interaction in brainstem potentials of human subjects.” Annals of neurology 9, pp. 384–93. Picton, T. W., John, M. S., Dimitrijevic, A., and Purcell, D. W. (2003). “Human auditory steady-state responses.” International journal of audiology 42, pp. 177–219. Riedel, H. and Kollmeier, B. (2002a). “Auditory brain stem responses evoked by lateralized clicks: is lateralization extracted in the human brain stem?” Hearing research 163, pp. 12–26. Riedel, H. and Kollmeier, B. (2002b). “Comparison of binaural auditory brainstem responses and the binaural difference potential evoked by chirps and clicks.” Hearing research 169, pp. 85–96. Ross, B. (2008). “A novel type of auditory responses: temporal dynamics of 40-Hz steady-state responses induced by changes in sound localization.” Journal of neurophysiology 100, pp. 1265–77. Ross, B., Tremblay, K. L., and Picton, T. W. (2007). “Physiological detection of interaural phase differences”. The Journal of the Acoustical Society of America 121, p. 1017.
AF 7
F7
FT 7
LE
T9
T7
T P7
P9
F5
AF 3
FP 2
F3
F1
FZ
AF 8
AF 4
AF Z
F4
F2
F8
F6
FC 5
FC 3
FC 1
FC Z
FC 2
FC 4
FC 6
C5
C3
C1
CZ
C2
C4
C6
CP 5
CP 3
CP 1
CP Z
CP 2
CP 4
CP 6
P7
P5
PO7
P1
P3
PO3
O1
PZ
POZ
OZ
P2
P4
PO4
P6
P8
FT 8
T8
T 10
13.7 Hz -45 ° +45 ° IPD Excursion 90°
The carrier was amplitude modulated using several rates (between 27 Hz and 109 Hz; IPD held at ±45◦). Example IPM-FRs from a single subject (Fig. 3) 1500
1500
SB:NH/Ch:t8 LE/Fc:520/Fm:41/Pc:33.8/Fj:1.7 RE/Fc:520/Fm:41/Pc:−33.8/Fj:1.7
PO8
O2
1500
SB:AR/Ch:t8 LE/Fc:520/Fm:41/Pc:33.8/Fj:3.4 RE/Fc:520/Fm:41/Pc:−33.8/Fj:3.4
1000
nV
1000
500
0
500
0 0
10
20 30 40 Frequency [Hz]
50
60
SB:AR/Ch:t8 LE/Fc:520/Fm:41/Pc:33.8/Fj:6.8 RE/Fc:520/Fm:41/Pc:−33.8/Fj:6.8
0.50 0.25
10
20 30 40 Frequency [Hz]
50
60
0
10
20 30 40 Frequency [Hz]
50
60
Simuli Experiment 2: Transposed tones at 2000 Hz, 3000 Hz and 4000 Hz (see Fig. 5). Temporal rate was 128 pps. IPMs (6.8 Hz) imposed on the transposed pulses were amplitude modulated at 41.0 Hz. IPD were ±90◦ or 0◦/180◦ (transposed phase of 90◦ at one and −90◦ at the opposite ear). 0.2 (a)
13.7 Hz
1.5 1.0 0.5 0.0 −0.5 −1.0 −1.5 0
0.00 6.8 Hz Amplitude (µV)
0.75 0.50 0.25 0.00
13.7 Hz
0.75
0.25 0.00 0
13.7 Hz
1.5 1.0 0.5 0.0 −0.5 −1.0 −1.5
0.50
0.1 0.2 0.3 0.4 0.5 Time (ms)
6.8 Hz
1.5 1.0 0.5 0.0 −0.5 −1.0 −1.5
10 20 30 Frequency (Hz)
40
0
0.75
6.8 Hz
500 600
0.50
0.00 0.75
13.7 Hz
0.50 0.25
0.1 0.2 0.3 0.4 0.5 Time (ms)
(b)
(c)
0.00 0
10 20 30 Frequency (Hz)
40
(a) Dichotic IPM-FRs (b) Diotic controls Figure 6: Average responses across subjects. Time and frequency responses for both 6a dichotic and 6b diotic controls are shown, respectively. The IPM rate is indicated above each panel.
IPM-FRs to several IPDs and IPM rates (see Fig. 7a). Non-parametric repeated measures analysis of variance (ANOVA) with factors Electrode Position (left/right mastoid), IPM rate, and IPD: IPM rate (p < 0.001) IPD (p < 0.001) IPM rate * IPD (p = 0.014) IPM-FRs to a fixed IPD and several modulation and IPM rates (see Fig. 7b). Non-parametric repeated measures ANOVA with factors Electrode Position (left/right mastoid), IPM rate, and modulation rate: IPM rate (p < 0.001) Modulation rate (p = 0.002) (ratio between lowest and highest IPM-FR was 1.8) Electrode position (p = 0.001) (right 8 % > left hemisphere) IPM rate * carrier amplitude modulation rate (p = 0.016)
IPM rate
IPM rate
0 −0.1
3.4
Stimuli Experiment 1: Carrier phases were symmetrically opposed in each ear in order to create IPDs that ranged between 11◦ and 135◦ (see Fig. 3).
6.8
6.8
13.7
13.7
(e)
0.14 0.15 Time [s]
0.16
0.17
(f)
0.13
0.14 0.15 Time [s]
0.16
0.17
(g)
0.13
0.14 0.15 Time [s]
0.16
0.17
(h)
Magnitude
0.03 0.02
Amplitude [nV]
0.04
0.13
Amplitude [nV]
−0.2 0.17
500
500
250
250
0
0
0.01 0
0
2000 4000 Frequency [Hz]
60000
2000 4000 Frequency [Hz]
60000
200
3000
3250
3500 3750 Carrier Rate [Hz]
4000
-1000
-500 0 500 Across ear carrier offset [Hz]
1000
(a) Matched cochlear regions (Figs. 5 (a),(e) and (b),(f) (b) Mismatched cochlear regions (Figs. 5(c),(g) and (d),(h)) Figure 8: IPM-FRs with transposed stimuli
Conclusions IPM-FRs could be reliably obtained. The SNR was largest for IPMs rates of 6.8 Hz and for IPDs between ±45◦ and ±90◦ at lower frequency regions. The IPM-FR may be more suitable than ABR based BIC as an objective measure of binaural processing.
Acknowledgments
References
3.4
750
IZ
0.16
200
300
(d)
750
0.14 0.15 Time [s]
400
400
IPD ± 90 0 / 180
The research leading to these results has received funding from the European Union’s Seventh Framework Programme (FP7/2007-2013) under ABCIT grant agreement number 304912.
0.1
0.13
IPD ± 90 0 / 180
0.25
0 0
(a) Example IPM-FR at 3.4 Hz IPM rate (b) Example IPM-FR at 6.8 Hz IPM rate (c) Example IPM-FR at 13.6 Hz IPM rate Figure 4: Examples IPM-FRs at different IPM rates. Significant responses (see Eq. 1) are shown by coloured markers.
RE
6.8 Hz
1.5 1.0 0.5 0.0 −0.5 −1.0 −1.5
3.4 Hz
Results of this pilot experiment demonstrated that IPM-FR could also be obtained at basal regions of the cochlea. Increasing carrier rates resulted in reduced response amplitude. Responses were significantly larger for the 0◦ to 180◦ condition than for the ±90◦ condition, suggesting than binaural processing relies on different mechanisms at basal sites of the cochlea. Responses obtained at different carrier rate offsets between ears agree with the hypothesis that interaural processing decreases when there is an across ear frequency mismatch.
Spectral magnitude [nV]
6.8 Hz -45 ° +45 ° IPD Excursion 90°
Figure 3: Stimuli used to elicit IPM-FRs. Top -45 ° +45 ° IPD panel: zoomed stimuli presented at the right Excursion (black) and left (gray) ear, respectively. 90° Bottom panel: same as top, in a large scale. Figure 2: Illustration of intracranial IPMs. Overtime, IPMs The leading phase is indicated by the color. produce moving intracranial transitions able to elicit IPM-FRs Different IPM rates present a large number of (real examples in Fig. 4). IPD transitions.
T P8
P 10
0.25
0.75
Spectral Magnitude (µV)
3.4 Hz
Amplitude
FP Z
FP 1
3.4 Hz
1.5 1.0 0.5 0.0 −0.5 −1.0 −1.5
0.50
Time
nV
Recordings and Data Analyses Recordings: Low-impedance headstage (20x gain). Unitary preamplifier. Fs: 25 kHz / 16 bits. Bandpass: 2.2 Hz and 7.5 kHz. Impedances < 5 kΩ. Data Analyses: Figure 1: Recording electrodes Epochs -> FFT of 100000 points (0.24 Hz of resolution). Frequency bins of interest were selected from each epoch. Significance -> two-dimensional repeated measurement Hotelling’s T 2 test (Picton et al., 2003). T 2 = N [¯ x , y¯ ]⊺ S −1 [¯ x , y¯ ] (1) Multiplying T 2 by (N − 2) / (2N − 2) produces an F distributed value with 2 and N − 2 degrees of freedom.
3.4 Hz
0.75
Spectral Magnitude (µV)
Time
500
Subjects Fourteen (ten took part in experiment 1 and four in experiment 2) NH listeners (hearing thresholds were below 20 dB normal Hearing Level (HL) for pure tones between 250 Hz and 8000 Hz). Research ethics was approved by UCL research ethics committee and all participants provided their informed consent prior the beginning of the experiments.
3.4 Hz
1.5 1.0 0.5 0.0 −0.5 −1.0 −1.5
0.00
Time
1000
Methods
Results - Experiment 2
IPM-FRs to several IPDs and IPM rates. Figure 6 shows time and frequency responses obtained with low rate sinusoidal carriers (see Fig. 3) for both dichotic and diotic controls.
IPMs were presented at 3.4 Hz, 6.8 Hz and 13.6 Hz. Since IPMs resulted in IPD fluctuations of opposite sign we will further refer to them as ± IPD. It must be noted that the IPD excursion is twice this value, i.e. if the IPD was modulated from 45◦ to −45◦ (±45◦), the overall IPD extrusion was 90◦ (see Fig. 2).
Amplitude (µV)
Bilateral cochlear implants (CIs) provide the opportunity for implant users to access binaural cues, potentially increasing performance in spatial listening tasks. However, since implants are inserted and fitted independently, users may have place-mismatched electrode arrays, effectively exciting the same cochlear sites across-ears with information from different frequency channels. The measurement of binaural processing has been a challenge for many years. The most common approach consists of a set of measurements where monaural auditory brainstem responses (ABRs) are summed and subtracted from a binaural ABR. This difference is believed to correspond to a measurement of binaural processing (e.g Levine, 1981; Riedel and Kollmeier, 2002a,b). However, this measurement has several disadvantages: it is an indirect measurement of binaural processing, the response is small and has a poor Signal-to-Noise Ratio (SNR). Alternatively, more direct objective measurements have been proposed. Dajani and Picton (2006) measured steady-state responses to noise signals where interaural correlations varied between 1 and 0 at a fixed rate. Similarly, Ross et al. (2007) and Ross (2008) used Magnetoencephalography (MEG) to record evoked cortical responses to binaural amplitude modulated sinusoidal stimuli containing abrupt interaural phase changes (IPCs) at a fixed rate of 0.5 Hz. The present study focused on the detection of binaural responses by means of interaural phase modulation following response (IPM-FR), by using a similar approach to Ross (2008). In a first experiment, we investigated the effect of interaural phase modulation (IPM) rate, interaural phase difference (IPD), and modulation frequency through electroencephography (EEG) recordings in Normal Hearing (NH) listeners at a low carrier rate (apical region of the cochlea). A second experiment investigated IPM-FRs by means of transposed tones. Transposed tones allowed us to simulate mismatched electrodes in the basal region of the cochlea since the envelope shape could be controlled independently of the carrier frequency.
Results - Experiment 1
Spectral magnitude [nV]
Methods
nV
Introduction
2000 4000 Frequency [Hz]
60000
2000 4000 Frequency [Hz]
6000
Figure 5: Transposed stimuli. (a) and (b) illustrate diotic carriers for ±90◦ and 0◦/180◦ IPD conditions, respectively. (c) and (d) illustrate time domain waveforms for dichotic carriers for ±90◦ and 0◦/180◦ IPD conditions (note that envelopes are identical for dichotic and diotic carriers). (e) to (h) Spectra of (a) to (b) responses, respectively. Note that for (e) and (f) left (blue) and right (red) spectra overlap.
± 11.3
± 22.5
± 45
± 67.5 IPD
± 90
± 112.5
± 135
27.3
41 54.7 68.4 82 95.7 Carrier amplitude modulation rate [Hz]
109.4
(a) IPM-FR as a function of the IPD (b) IPM-FR as a function of the modulation rate Figure 7: IPM-FRs as a function of both 7a IPD and 7b for all IPM rates (color coded).
Dajani, H. R. and Picton, T. W. (2006). “Human auditory steady-state responses to changes in interaural correlation.” Hearing research 219, pp. 85–100. Levine, R. a. (1981). “Binaural interaction in brainstem potentials of human subjects.” Annals of neurology 9, pp. 384–93. Picton, T. W., John, M. S., Dimitrijevic, A., and Purcell, D. W. (2003). “Human auditory steady-state responses.” International journal of audiology 42, pp. 177–219. Riedel, H. and Kollmeier, B. (2002a). “Auditory brain stem responses evoked by lateralized clicks: is lateralization extracted in the human brain stem?” Hearing research 163, pp. 12–26. Riedel, H. and Kollmeier, B. (2002b). “Comparison of binaural auditory brainstem responses and the binaural difference potential evoked by chirps and clicks.” Hearing research 169, pp. 85–96. Ross, B. (2008). “A novel type of auditory responses: temporal dynamics of 40-Hz steady-state responses induced by changes in sound localization.” Journal of neurophysiology 100, pp. 1265–77. Ross, B., Tremblay, K. L., and Picton, T. W. (2007). “Physiological detection of interaural phase differences”. The Journal of the Acoustical Society of America 121, p. 1017.
