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, 37 (5), e291-301

Test-Retest Reliability of the Binaural Interaction Component of the Auditory Brainstem Response

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Test-Retest Reliability of the Binaural Interaction Component of the Auditory Brainstem Response

Alexander T Ferber et al. Ear Hear.

Abstract

Objectives: The binaural interaction component (BIC) is the residual auditory brainstem response (ABR) obtained after subtracting the sum of monaurally evoked from binaurally evoked ABRs. The DN1 peak-the first negative peak of the BIC-has been postulated to have diagnostic value as a biomarker for binaural hearing abilities. Indeed, not only do DN1 amplitudes depend systematically upon binaural cues to location (interaural time and level differences), but they are also predictive of central hearing deficits in humans. A prominent issue in using BIC measures as a diagnostic biomarker is that DN1 amplitudes not only exhibit considerable variability across subjects, but also within subjects across different measurement sessions.

Design: In this study, the authors investigate the DN1 amplitude measurement reliability by conducting repeated measurements on different days in eight adult guinea pigs.

Results: Despite consistent ABR thresholds, ABR and DN1 amplitudes varied between and within subjects across recording sessions. However, the study analysis reveals that DN1 amplitudes varied proportionally with parent monaural ABR amplitudes, suggesting that common experimental factors likely account for the variability in both waveforms. Despite this variability, the authors show that the shape of the dependence between DN1 amplitude and interaural time difference is preserved. The authors then provide a BIC normalization strategy using monaural ABR amplitude that reduces the variability of DN1 peak measurements. Finally, the authors evaluate this normalization strategy in the context of detecting changes of the DN1 amplitude-to-interaural time difference relationship.

Conclusions: The study results indicate that the BIC measurement variability can be reduced by a factor of two by performing a simple and objective normalization operation. The authors discuss the potential for this normalized BIC measure as a biomarker for binaural hearing.

Conflict of interest statement

The authors have no conflict of interest to declare.

Figures

Figure 1
Figure 1
BIC recordings and reproducibility. A) Definition of the BIC: ABR waveforms obtained from monaural stimulations (blue: left, red: right) are summed to obtained the “Sum” waveform. The BIC is obtained by computing the difference between the waveform obtained by binaural stimulation (green) and the “Sum” waveform. When ITD is present in binaural stimulation, monaural waveforms are appropriately time-shifted prior to summation to match the binaurally presented ITD. The BIC amplitude is the amplitude of the DN1 peak. B) Electrode montage: The vertex-nape electrode montage employs an active electrode at the vertex and a reference electrode at the nape of the neck, with a third ground electrode placed at a distal site (here, at the hind leg). Both electrodes are midline, receiving symmetric contributions to the ABR signal and emphasizing central generators of the ABR waveform. C) Amplitude of the BIC DN1 peak measured as a function of ITD in one animal, over a range of ITD cues spanning ±2 ms. Different curves represent the same experiment conducted on 4 different days.
Figure 2
Figure 2
BIC amplitude at 0 ITD is affected by long term hearing loss (see text, blue and green dots), which could be the result of two transformations of the BIC amplitude to ITD relationship (blue curve): a global scaling of BIC DN1 amplitude across ITDs (A, green curve), or a lateral shift of the relationship curve toward nonzero ITDs (B, green curve).
Figure 3
Figure 3
Reproducibility of the relationship between BIC and ITD. A) BIC DN1 peak amplitude plotted as a function of ITD for eight animals, with 3-5 repeated measurements per animal. Shaded regions represent ±1 standard deviation of DN1 amplitude from the mean. B) Mean DN1 peak amplitude versus ITD cue is plotted for each of eight animals above. C) Population mean for DN1 peak amplitude is plotted versus ITD for eight animals, with ±1 standard deviation for the population mean depicted in gray.
Figure 4
Figure 4
Model of the relationship between BIC and ITD. A) Gaussian fits to DN1 amplitude against ITD for each day for each animal (different days are represented by different shades); B) Schematics of the four parameters resulting from the Gaussian fit. A and B are magnitude parameters expressed in μV, ITD0 and σ are expressed in ms. C) Scatter plot of the value of A for each measured BIC curve (all animals, all repetitions) plotted against the average RMS of the response to monaural stimulations (see text). D) Same as panel C, for the values of B. E) Same as panel C for the values of ITD0, F) Same as panel C for the values of σ. The mean of monaural ABR RMS waveform amplitudes =(LRMS + RRMS)/2.
Figure 5
Figure 5
DN1 amplitudes normalized to the average monaural ABR RMS are consistent and have ample amplitude range across physiologic ITDs. A) Normalized DN1 amplitude from individual experiments is plotted versus ITD per animal with ±1 standard deviation shown in gray; Theoretical range of BIC amplitude (see Text) is depicted with dashed lines. B) Mean DN1 peak amplitude within subjects normalized to [LRMS + RRMS] is plotted versus ITD cue for each of eight animals above; C) Normalized population mean for DN1 peak amplitude is plotted versus ITD for eight animals, with ±1 standard deviation for the population mean depicted in gray. Systematic variability is reduced, enough that subtle changes to DN1 amplitude in the physiologic range of ITD cues are more easily detected.
Figure 6
Figure 6
Wave III amplitude normalization. A) Comparison of different normalization. Each curve represents the BIC amplitude measured in number of standard deviations across the population (see Text). Blue curve is normalization to monaural ABR RMS, green curve to Wave III amplitude, and black curve is raw data. Normalization provides a greater dynamic range across ITDs. B) Wave III amplitude at 0 ITD correlates strongly with the monaural ABR RMS defined above.
Figure 7
Figure 7
Testing for abnormal BIC. A) Schematics of the simulation procedure. Top row: A given BIC vs ITD recording is picked out of all the available ones (N=29), and altered in one of three ways (additive or multiplicative scaling, ITD shifting). Bottom row: The rest of the population’s BIC recordings are averaged, and a Gaussian fit is applied to the average BIC to obtain the “template”. Bottom-right corner: the altered BIC is compared against the “template”, and the RMS error recorded. This procedure is then replicated by picking another BIC to alter, and/or varying the parameter of the alteration. See Methods for details. B-G) Each panel displays the fit quality as a function of the alteration parameter (colored shaded area: line is mean, area is ± 1 s.d.). In each panel the baseline variability (see Text) is represented (gray area). For parameter values where the colored and gray areas do not overlap it is easy to distinguish the altered BIC from the population. B-D uses normalized BIC values, E-G uses the raw data.

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