Effects of stimulus parameters on human evoked potentials to shifts in the lateralization of a noise.

Changing the interaural time difference (ITD) of a continuous binaural noise causes a shift in the perceived lateralization of the noise and evokes a late auditory evoked potential with negative peak at 130 ms and a positive peak at 220 ms. The response is mainly evoked by stimulus frequencies below 2,000 Hz and is mediated through the middle and apical regions of the cochlea. The threshold for perceiving the lateralization reversal and for eliciting a clear evoked potential is approximately 15 dB higher than the intensity required to perceive the onset of the noise. Increasing the ITD up to 1.0 ms increases the amplitude of the evoked potential and the perceived lateralization of the noise. Further increases in the ITD decrease the amplitude of the evoked potential and make the perception of the sound less 'compact'. Decreasing the intensity of the sound in one ear decreases the response to a change in ITD, but recognizable responses occur with interaural intensity differences up to 30 dB.