Changes in the late positive wave of auditory evoked potentials in simple reaction--time tasks.

A comparison is made of the averaged evoked potentials (AEP) to auditory signals obtained in three different series: (a) a series consisting of high tones only to which no motor response was required; (b) a series consisting of low tones only in which quick motor response was required; (c) a series consisting of the same low tones and elimination of the requirement for quick motor response. It was found that the late positive wave P3 of AEP changed in the different series. In the series requiring no motor response P3 was poorly expressed, in the series requiring quick motor response P3 markedly increased and in the series in which the requirement for quick motor response was eliminated, it decreased again. The AEP configuration from the last series repeated that obtained from the indifferent signals. Moreover, on evoked potentials to signal trials and analysis was made of the dispersions in the P3 latencies under conditions requiring motor response. Their difference was found to be insignificant. The results obtained are explained by the assumption that the wave P3 reflects the activity of the central nervous system related to evaluation of the outcome and with the result of the prediction and the planned speed of the motor response.