Patterns of event runs in probability learning

Forty-eight Ss were assigned to a 2 by 2 factorial design with two levels of risk (1¢ and A¢) and two levels of sequence (patterned-run distribution and random-run distribution) in a two-choice probability learning task. All Ss received 300 trials. Conditional predictions were not affected by differences in risk. A significant effect of the sequence variable was found in responding conditional on runs of the less frequent event, but not in responding conditional on runs of the more frequent event. It was concluded that Ss respond to certain higher order regularities in the event-run structures.