The auditory brainstem response to binaural delayed stimuli in man.

The brainstem responses (BER) evoked by binaural clicks (0.1 ms) with interaural time differences (delta t) from 0 to 3.5 ms were studied in 6 normal subjects. The responses analysis was carried out via computer in two different ways: (a) Comparison between binaural BER and templates obtained with the addition of two monaural BERs. (b) Extraction from the binaural BER of the second delayed pattern. The results suggest that an algebraic addition of the responses from the two stimulated sides is the main mechanism of the binaural BER generation. In comparison with the templates, the binaural response shows some differences which are evident at delta t = 0--1.5 ms and are limited in the region of VI and VII waves. Such differences are caused essentially to an amplitude decrease of the second pattern--that is response to the delayed stimulus--mainly at delta t 1.5 ms. However these results do not allow us to say if the phenomenon recorded at the surface is due to central adaptation or to specific mechanism of binaural interaction.