Change in prediction confidence was studied as a determinant of the sequential effects of prediction outcome (PO) in a two-stimulus, two-response reaction time task. In a between-groups experiment, the RTs of "consonant" Ss, whose average confidence in a stimulus prediction increased following correct POs and decreased following incorrect POs, were reliably influenced by preceding PO. In contrast, "dissonant" Ss, whose average confidence decreased following correct POs and increased following incorrect POs, exhibited no reliable effect of preceding PO on RT. Analogous results were obtained in a within-Ss experiment when each trial was categorized according to the relationship between preceding PO and Ss statements of having "more" or “less" prediction confidence than on the previous trial. “Consonant” trials, on which Ss indicated “more" confidence following correct POs and "less" following incorrect POs evidenced a significantly greater preceding PO effect on RT than did "dissonant" trials. The results partially support a continuous expectancy model of the sequential effects of PO on choice RT. / Master of Science