Human evoked potentials and the lateralization of a sound.

If an identical noise is presented to each ear with one ear receiving the noise slightly earlier than the other, the listener perceives the sound as originating from the side of the leading ear. If the interaural time-difference reverses, the subject perceives a shift in the lateralization of the sound to the other ear. This shift in lateralization evokes a late auditory potential with a negative wave at 135 ms and positive waves at 75 and 220 ms. This evoked potential specifically indexes central auditory processing since information about the timing of the auditory stimuli must be compared between the two ears. The response increases in amplitude with increasing interaural time-difference reaching maximum values between 0.3 and 1.5 ms. The response is evoked through acoustic frequencies below 2,000 Hz. In patients with multiple sclerosis the response is often abnormally delayed or small. The response may therefore be helpful in the clinical evaluation of patients with central auditory dysfunction.