The effect of binaural masking noise disparity on human auditory brainstem binaural interaction components

The binaural interaction components (BIC) of the human auditory brainstem responses have been associated with sound lateralization which involves analyzing correlated inputs from the two ears. To test the hypothesis that BIC generators are specifically sensitive to binaural, correlated sounds, the effects of monaural and binaural correlated and uncorrelated masking on BIC to clicks were compared. Analysis included peak-to-prestimulus baseline amplitudes and latencies of BIC peaks from the vertex-mastoid ('A') and vertex-neck ('Z') channels, as well as the three-channel Lissajous trajectory (3-CLT) measures. Trajectory amplitudes of BIC BdIII, BeI and BeII were significantly suppressed by correlated (but not by uncorrelated) binaural noise, when compared with the unmasked condition. Moreover, component BdIII was more affected by masking with correlated than with uncorrelated binaural noise. Overall, binaural noise was more effective in suppressing BIC then monaural noise, and interaurally correlated binaural noise was more effective than uncorrelated binaural noise. These results are compatible with BIC generation by a binaurally activated subset of central auditory neurones which is sensitive to interaurally correlated sounds. Such a subset has been associated with the superior olivary complex and is assumed to be involved in sound lateralization.