Effects of fixed-time shocks and brief stimuli on food-maintained behavior of rats

Topographical aspects of brief-stimulus presentations: A re-examination of the problem of conditioned reinforcement

Three pigeons were exposed to second-order schedules in which responding under a fixed-interval (FI) component schedule was reinforced according to a variable-interval (VI) schedule of food reinforcement. Completion of each component resulted in either (1) brief presentation of a stimulus present during reinforcement (paired brief stimulus), (2) brief presentation of a stimulus not present during reinforcement (nonpaired brief stimulus), or (3) no stimulus presentation (tandem schedule). Under the two nonpaired brief stimulus conditions, either a change in keylight color or onset of houselight illumination was used as the brief stimulus. Similar patterns of keypecking occurred under tandem and nonpaired keylight brief-stimulus presentations, whereas nonpaired houselight brief-stimulus presentations generated positively accelerated within-component keypeck patterning for two pigeons. When the same keylight brief stimulus was paired with food, positively accelerated patterns of keypecking were obtained for all pigeons. Differences in the effects of nonpaired brief-stimulus presentations on second-order schedule performance suggest that component schedule patterning under nonpaired brief-stimulus procedures is a function of the particular type of stimulus used (i.e., houselight versus keylight). These results suggest that (1) brief houselight illumination may function as a sensory reinforcer, and (2) a briefly presented food-paired stimulus can function as an effective conditioned reinforcer.

Within-subject testing of the signaled-reinforcement effect on operant responding as measured by response rate and resistance to change

Response rates under random-interval schedules are lower when a brief (500 ms) signal accompanies reinforcement than when there is no signal. The present study examined this signaled-reinforcement effect and its relation to resistance to change. In Experiment 1, rats responded on a multiple random-interval 60-s random-interval 60-s schedule, with signaled reinforcement in only one component. Response resistance to alternative reinforcement, prefeeding, and extinction was compared between these components. Lower response rates, and greater resistance to change, occurred in the component with the reinforcement signal. In Experiment 2, response rates and resistance to change were compared after training on a multiple random-interval 60-s random-interval 60-s schedule in which reinforcer delivery was unsignaled in one component and a response-produced uncorrelated stimulus was presented in the other component. Higher response rates and greater resistance to change occurred with the uncorrelated stimulus. These results highlight the significance of considering the effects of an uncorrelated signal when used as a control condition, and challenge accounts of resistance to change that depend solely on reinforcer rate.