Changes in the P3-wave in a situation of verbal stimulus prediction

The changes in the P3-wave of averaged auditory evoked potentials (AEP) from Fz, Cz and Pz were studied under conditions when: (I) the subject was required to predict which of the two alternative sound stimuli would appear. After presentation of a series of 50 high (1200 Hz) and 50 low (800 Hz) tones, in random order (mixed signal series) we proceeded suddenly to the presentation of the low tone only, without warning the subject (pseudo-mixed series); (II) the same mixed signal series was presented again requiring quick motor response by the subject only to the appearance of the high tone and not requiring verbal prediction (choice RT task). It has been found that in the three recordings: (1) the P3-wave increases for both types of stimuli, both in the situation of verbal stimulus prediction without motor response and in the situation of choice RT task; (2) the increase in P3 (assessed by the N1-P3 amplitude) is greater in AEP from stimuli disconfirming the prediction compared with stimuli confirming it; (3) preforming of the verbal prediction, in the course of the pseudo-mixed series, to prediction of the appearance of the low tone only is accompanied by a sharp decrease or disappearance of the P3-wave. The results show that the P3-wave is not connected with the development of motor potentials but with the processes of verbal prediction, in particular with the non-coincidence between the event expected by the subject and the really appearing one.