APPETITIVE BACKWARD CONDITIONING IN PIGEONS

A systematic replication of Hearst's (1989) demonstration of excitatory, appetitive backward conditioning with pigeons was undertaken. On each training session, two types of backward conditioning trials were presented:'On positive trials, hopper presentation (the unconditioned stimulus, or US) was followed by illumination of a pigeon key (the positive backward conditioned stimulus, or CS) for 6 s. On negative trials, a different 6-s keylight (the negative backward CS) followed presentation of the hopper light alone. Associative strength was assessed on higher-order, summation, resistance-to-reinforcement, and extinction test sessions, using two measures-key pecking and key approach (proximity duration). Consistent with Hearst's findings, pigeons rarely pecked during backward conditioning training; however, during resistance-to-reinforcement tests, birds acquired keypeck responding more rapidly to the positive versus the negative backward cue. In Experiment 2, maintained proximity duration was higher to the positive versus the negative CS on resistance-to-reinforcement tests in both between- and within-subject comparisons. These results, which extend those of Hearst to a within-subject assay of backward conditioning, and to an alternate measure of performance, suggest that appetitive backward conditioning is a reliable phenomenon, the parameters of which require further exploration.