Abstract
Two experiments with rats examined competition between simultaneous and serial features for behavioural control in an appetitive discrimination. In Experiment 1, an auditory target was reinforced when presented in isolation. For different groups, the target was non-reinforced when simultaneously accompanied by a visual feature (first group), when preceded by a serial visual feature (second group), or when both accompanied by a simultaneous feature and preceded by a serial feature (third group). Tests performed after discrimination learning revealed inhibitory control by the simultaneous feature in the first group and by the serial feature in the second group. In the third group, the simultaneous feature acquired inhibitory control over the target in isolation, whereas the serial feature did not. However, the serial feature further reduced responding to the target-simultaneous feature compound relative to responding shown to the compound in isolation. In Experiment 2, the same training procedure was used in three groups as in Experiment 1, except that the target was nonreinforced in isolation and reinforced in the presence of a simultaneous and/or serial feature. Tests revealed that the feature acquired excitatory control in the first and second groups. In the third group, both features acquired excitatory control, although the control exerted by the simultaneous feature was less strong than that observed in the group trained with only the simultaneous feature. The theoretical implications of these results regarding competition between occasion setters and Pavlovian excitors and inhibitors were discussed.