Comparison of brain stem auditory evoked potentials for monaural and binaural stimuli.

This study examined the relation of brain stem auditory evoked potentials (BAEPs) for monaural and binaural click stimuli. Responses were recorded from normal subjects for 4 stimulus levels of 50, 70, 90 and 110 dB peSPL peak-to-peak, corresponding to monaural sensation levels of 7, 27, 47 and 67 dB SL. Wave amplitude and latency values were analyzed for the effects of the binaural stimulus condition. Responses to binaural stimuli were compared to the summed responses to monaural stimuli to estimate binaural interactions. The results show that responses to a binaural stimulus have significantly greater wave amplitudes than responses to a monaural stimulus. If a response to a binaural stimulus is compared to the sum of the responses to the corresponding monaural stimuli, however, there are no significant differences in wave V amplitudes. Latency values are equal for the two stimulus conditions. Calculations of a continuous wave form representing the difference (point-by-point) between the response to a binaural stimulus and the summed response to the two monaural stimuli shows that significant binaural interactions occur with a latency of 7-10 msec. Additional interactions occur with a latency of 12-16 msec. Although neural and sonomotor sources may contribute to these short latency binaural interactions, acoustic cross-talk appears to account for a significant portion of the observed interaction.