Signal modality and choice between signaled and unsignaled food.

Choice between signaled and unsignaled response-independent food schedules was assessed in three experiments using a commitment procedure. In Experiment 1, subjects tested with a 5-s visual signal consistently changed from the signaled to the unsignaled schedule. Changing from the unsignaled to the signaled schedule was observed only occasionally and only at low levels. The same outcome was observed in Experiment 2 with different types of visual signals and with different stimulus combinations identifying the signal period, the signal-absent period, and the unsignaled schedule. In Experiment 3 the visual signal was replaced with an auditory signal for four of the subjects tested in Experiment 2. The subjects then changed from the unsignaled to the signaled schedule or showed a substantial reduction in choice for the unsignaled schedule. The data were assessed using a conditioned-reinforcement interpretation of choice.