Behavioural control by simultaneous and serial features in feature-positive and feature-negative discriminations

Two experiments with rats examined behavioural control by feature stimuli in appetitive conditioning using latency of food-magazine visits as the dependent measure. In experiment 1, a feature-positive (FP) discrimination was presented in which a target stimulus was consistently followed by food when preceded by a serial feature and accompanied by a simultaneous feature, and not followed by food when presented alone. The reverse condition, a feature-negative (FN) discrimination procedure, was in effect in experiment 2. Groups of rats differed in the physical identity of the stimuli used as target and features. In the FP discrimination, all groups came to respond faster on reinforced than on nonreinforced trials. Subsequent tests revealed that the serial feature was responsible for this performance in all groups, whereas the simultaneous feature had not acquired significant control in all groups. Only one half of the groups solved the FN discrimination and they did this on the basis of only the simultaneous feature, which was a relatively intense stimulus in these groups. These results suggest a propensity to use the serial feature in FP discriminations and the simultaneous feature in FN discriminations.