Binaural interaction in human auditory evoked potentials.

Binaural interaction (BI) in auditory evoked potentials was defined as any deviation from the predictions of a model which assumes two independent populations of neurons whose outputs are, in the far field, simply additive. Monaural responses are added to yield the model's prediction of binaurally evoked response; this trace is then subtracted from the actual binaural response to yield a difference trace which is considered to represent BI. In a previous study, strong BI was seen in guinea pig BSEP, maximal at about 4 msec latency; the interaction was greatest for simultaneous (delta t = 0) stimuli of equal intensitsy (delta I = 0). Sixteen normal young adults had BSEP and middle-latency auditory evoked potentials (middle AEP) recorded in response to binaural and monaural clicks. Although BI (in the 6 msec latency region) was observed in the difference trace for the majority of subjects' BSEP, there were no significant differences between binaural and predicted-binaural responses in the group means for individual peak amplitudes and latencies. In middle AEP, the amplitude of peak Pa was usually much smaller in binaurally evoked responses than in the predicted-binaural response. Four subjects had middle AEP which were felt to be predominantly myogenic on the basis of short latency and large amplitude; these responses demonstrated a reverse pattern of interaction, with binaural responses much larger than the monaural sums.