title: Effect of the verbal instruction on the late positive wave P3 of auditory evoked potentials in human subjects.
abstract: The changes in the late positive wave P3 of the averaged evoked potentials (AEP) are studied under conditions when: (a) only high tones were presented requiring no motor response; (b) only low tones were presented requiring motor response; (c) the subject was instructed that the two types of tones will be presented in random order with a definite probability (50%:50% or 25%:75%, or conversely 75%:25%) requiring motor response only to the low tones. In fact, however, only high tones were presented to which no motor response was required (pseudo-mixed series). It has been established that under the effect of the verbal instruction used, the P3 wave of the AEP of the pseudo-mixed series increased at the beginning of the series, and thereafter the P3 "behaviour" was different with the different subjects: (1) In some of them P3 persisted until the presentation of a definite number of signals (different for the individual subjects) and afterwards it disappeared; (2) In some others P3 now increased now disappeared in a manner different for the different subjects; (3) Subjects in which P3 remained pronounced throughout the entire series; they also "heard" low tones. All these changes in P3 did not depend on the probability characteristics of the pseudo-mixed series ascribed by the instruction. The dependence of the late positive wave P3 on the processes of probability prediction in the human brain functioning, and on the changes in the arousal, is discussed.
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D003142:Communication; D004569:Electroencephalography; D004585:Electrooculography; D005071:Evoked Potentials; D005260:Female; D006801:Humans; D008297:Male; D011337:Probability Learning / Q000502:physiology; D013997:Time Factors