The Relation of P300 Latency to Reaction Time as Function of Expectancy

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Book Chapter

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This chapter discusses the relation of P300 latency to reaction time as a function of expectancy. The amplitude of the P300 component of the event-related potential (ERP) is inversely related to the subjective probability, or “expectancy,” for a task-relevant event. The assertion that P300 reflects the timing of stimulus evaluation has sometimes been interpreted as implying that P300 latency is positively correlated with reaction time (RT). The finding that, under certain conditions, P300 and RT is dissociated need not, however, cast doubt on the validity of P300 latency as a measure of processing time. Data showing dissociation may be reconciled by noting that the subject's response is only one of many possible consequences of stimulus presentation, rather than the end point of information processing activities invoked by a stimulus. It is thus plausible to expect P300 latency to be determined by one subset of the processes invoked by a stimulus and RT to be determined by another. Since stimuli may initiate multiple, parallel processes, the relative timing of P300 and RT would then depend on the degree of overlap between the processes of stimulus evaluation and response selection.

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The Relation of P300 Latency to Reaction Time as Function of Expectancy, in H. H. Kornhuber & L. Deecke (Eds.), Motivation, Motor and Sensory Processes of the Brain: Electrical Potentials, Behavior and Clinical Use: Progress in Brain Research, Elsevier, p. 717-722