CODING OF FEATURE AND NO-FEATURE EVENTS BY PIGEONS PERFORMING A DELAYED CONDITIONAL DISCRIMINATION

Pigeons' performance of a delayed conditional discrimination with pres ence versus absence of conditional (sample) stimuli was examined in tw o experiments. The pigeons showed steeper retention functions with fea ture (i.e., presence) samples (either food or yellow) than with no-fea ture (i.e., absence) samples (either no food or no yellow). These resu lts suggest that pigeons code features and respond only by default to test stimuli (comparisons) associated with no features. In contrast, t he overall superiority of performance on no-feature-sample trials comp ared with feature-sample trials in both the food/no-food- and yellow/n o-yellow-sample tasks was reversed at a 0-sec delay in the food/no-foo d-sample group, but not in the yellow/no-yellow-sample group. This dif ference in results with hedonic versus nonhedonic samples suggests tha t the crossover in delay performance on food/no-food-sample trials is produced by the formation of backward associations between the food-as sociated comparison stimulus and the food sample.