Stimulus versus response probability effects in choice reaction time

Abstract

The effects of stimulus and response probability on choice reaction time (RT) were independently investigated. In different conditions, two sets of three stimuli of probabilities of.1, .3, .6 and.3, .3, .4 were assigned to two responses-two of the stimuli assigned to one response. All combinations of S-R assignments were studied, yielding response probabilities of .1-.9,,3-.7, and,4-.6. With response probability held constant, variations in stimulus probability led to consistent and substantial effects on both RT and error rates. Response-probability effects were confined to error rates, and repetition effects were negligible. The results support the assumption of recent models of choice behavior that adjustments are made to the absolute (rather than just to the ordinal) values of stimulus probability. © 1970 Psychonomic Society, Inc.