ON and OFF components in the auditory evoked potential

Abstract

It has been suggested that the ON and OFF components of the auditory evoked potential (AEP) may be mediated by independent physiological mechanisms and that the response to a brief tone consists of overlapping ON and OFF responses. Two experiments were performed to evaluate these proposals. First, AEPs were recorded to tonebursts of various durations presented at a fixed rate. As the tonebursts were made longer, they evoked smaller ON responses and larger OFF responses, particularly when either response followed the other by less than 5 sec. This indicates that ON and OFF responses are not physiologically independent. Second, the AEP to a 25-msec tone was compared with the ON response to a 2,000-msec tone. At an interstimulus interval of 4 sec, the difference wave formed by subtracting the latter AEP from the former contained clear N 1 (ca. 100 msec) and P 2 (ca. 180 msec) components, which have been interpreted as an OFF response by some authors. These components in the difference wave were greatly reduced or even inverted at 10-sec interstimulus intervals, however, where interactions between ON and OFF responses to successive stimuli were minimized. This result indicates that any residual OFF response in the AEP to a brief tone is very small in amplitude, if present at all. © 1978 Psychonomic Society, Inc.