Temporally discriminated operant responding in fish
In Experiment 1, groups of 10 goldfish and of 10 grey mullet were trained to press a lever for food under a fixed, daily, light cycle. The periods during which responses were reinforced were restricted to two, 1-hr periods in every 24 hrs. These periods occurred at the same time each day. Responses were coordinated with the temporal contingencies of the schedule, and this pattern persisted for a number of days when no responses were reinforced. Experiment 2 demonstrated that a fixed light cycle was not essential for the maintenance of temporal discrimination. Experiment 3 followed a similar procedure to that of Experiment 1, except with individual goldfish and with only one, 1-hr feeding period in every 24. Experiment 4 produced evidence that temporal discrimination could develop under continuous illumination in individual goldfish. In Experiment 5, individual goldfish under continuous illumination were exposed to schedules that reinforced lever presses with food during a 1-hr period each day. Training with simultaneous temporal and visual contingencies, where food was available only in the presence of a stimulus light and at the same time each day, did not attenuate control over responding by either contingency. Further, pretraining on the temporal contingency did not prevent the subsequent acquisition of control by a stimulus light that was presented during the feeding hour. Similarly, pretraining on a visual contingency in which food was available at a different time each day did not prevent the subsequent acquisition of control by the temporal contingency (established by fixing the time of food availability). In Experiment 6, pretraining on the visual contingency did attenuate the subsequent acquisition of control by a different visual stimulus, showing that the lack of interference in control observed in Experiment 5 was not simply due to the intertrial interval used. These findings suggest that concurrent temporal and visual contingencies may control behaviour in parallel rather than in a competitive manner.