Binaural interaction in brainstem-evoked responses.

Binaural interaction (BI) in brainstem-auditory-evoked responses (BSERs) was defined as any deviation from the predictions of a model that assumes two independent monaural BSER generators whose outputs are additive. Brainstem-auditory-evoked responses were recorded in response to right (R) monaural, left (L) monaural, and binaural click stimuli. The monaural BSERs were added to give the model's prediction (P) of binaurally evoked BSER (P = L + R), and this trace was then subtracted from the actual binaurally evoked response (B). The resultant difference trace (d = b - p) represents the derived BI. In each of ten guinea pigs, a strong BI was present in the peak IV region (latency = 3.5 to 4.0 ms). This interaction is probably present with interaural intensity differences of up to 40 dB and interaural time differences of up to 3 ms. Preliminary studies suggest the presence of a similar phenomenon in human BSERs.