Auditory tract asymmetry in brainstem electrical responses during binaural stimulation.

A recently developed technique to demonstrate binaural interaction in brainstem auditory electrical responses was systematically investigated. From analysis of the BSERs of eight normal hearing adults, it was found that variations in binaural interaction difference traces are related to an artificial relationship created by this technique between the true binaural and summed monaural waveforms. The present investigation employed a refinement of the binaural interaction technique whereby left and right monaural waveforms were subtracted individually from the binaural waveform to produce a difference trace. Analysis revealed that variations in the difference trace morphology are related to dependence of binaural latencies on left or right auditory tract preference in the brainstem auditory pathways. Within the subject population, 50% demonstrated an auditory tract preference for binaural latencies while 50% showed no preference. It was concluded that the difference trace is mathematically predictable from the morphological differences between the binaural and monaural waveforms and that a more accurate representation of binaural interaction can be obtained from a comparison of individual monaural waveforms within the binaural trace.