Effects of interaural time and level differences on the binaural interaction component of the 80 Hz auditory steady-state response.

The auditory steady-state evoked response (ASSR) is a scalp-recorded potential elicited by modulated sounds or repetitive transient sounds presented at a high rate. The binaural interaction component (BIC) of the ASSR equals the difference between the response to binaural stimuli and the sum of the responses to a monaural stimulus presented to the left ear and the right ear. This study examined the effect of the interaural time (ITD) and level (ILD) difference on the BIC of the 80 Hz ASSR. Sixteen human participants with normal hearing were tested. The ITD and ILD were varied from -1.6 to +1.6 msec and from 0 to +12 dB, respectively. The ITD function of the BIC showed a "V" shape, with a 0 value of BIC at ITD 0 msec and a positive BIC at ITD +0.8 to +1.6 msec. For ILD conditions, the BIC displayed negative values, and its amplitude became more negative as the ILD was increased. The results indicate that the ITD and ILD may be processed by different groups of binaural neurons in different pathways. It is suggested that the 80 Hz ASSR provides an objective means for evaluating binaural functions in patients such as those with central auditory processing disorders.