Priming during multiple-target search: The cumulative effects of relative target frequency

Abstract

During search for multiple targets, reaction time decreases when a given target assumes a relatively high probability of appearance. Three experiments addressed the basis of this frequent-target effect. In a trialwise visual search method, pigeons pecked at the single target symbol embedded in a multisymbol display. In Experiment 1, the course of reaction times to frequent and infrequent targets was followed over extended sessions; reaction time to the frequent target dropped gradually over the first 200–400 trials. In Experiment 2, extinction sessions were introduced; the frequent-target effect persisted in the absence of reinforcement. In Experiment 3, the role of local trial patterns was examined; the frequent-target effect resisted temporary variations in relative target probability. Facilitation of search for high-probability targets appears to be an attentional rather than a conditioning effect; in the present design, information summarized over large sequences of trials appeared to provide pretrial information that primed attention.