UC Irvine

A waveform subtraction procedure, in which evoked potentials to rare tones (p=.15) in an Ignore condition were subtracted from the analogous waveforms in an Attend condition, revealed the existence of a previously unreported positive potential with a latency of approximately 165 msec (P165) which is related to cognitive stimulus processing. The potential was absent for frequent background tones. An analysis of latency and scalp distribution data showed that P165 could be differentiated from the stimulus‐evoked P200 potential, and experiments in which muscle tension was varied did not change the form of P165, supporting a neurogenic origin. Most likely P165 is an early manifestation of decision processes related to the later N200 and P300 potentials. Copyright © 1978, Wiley Blackwell. All rights reserved