CONTEXT EFFECTS ON CHOICE

Four pigeons responded on a concurrent-chains schedule in four experim ents that examined whether the effectiveness of a stimulus as a condit ioned reinforcer is best described by a global approach, as measured b y the average interreinforcement interval, or by a local contextual ap proach, as measured by che onset of the stimulus preceding the conditi oned reinforcer. The interreinforcement intel val was manipulated by t he inclusion of an intertrial interval, which increased the overall ti me to reinforcement but did not change the local contingencies on a gi ven trial. A global analysis predicted choice for the richer alternati ve to decrease with the inclusion of an intertrial interval, whereas a local analysis predicted no change in preference. Experiment 1 examin ed sensitivity to intertrial intervals when each was signaled by the s ame houselight that operated throughout the session. In Experiment 2, the intertrial interval always was signaled by the stimulus correlated with the richer terminal link. In Experiment 3, the intertrial interv al was signaled by the keylights correlated with the initial links and two novel houselights. Experiment 4 provided free food pseudorandomly during the intertrial interval. In all experiments, subjects' prefere nces were consistent with a local analysis of choice in concurrent cha ins. These results are discussed in terms of delay-reduction theory wh ich traditionally has failed to distinguish global and local contexts.