Punishment of schedule-induced drinking in rats by signaled and unsignaled delays in food presentation

Food-deprived rats were exposed to a fixed-time 60-s schedule of food-pellet presentation and developed schedule-induced drinking. Using an ABA reversal design, three experiments investigated the effects of events then made dependent on licks. In Experiment 1, lick-dependent signaled delays (10 s) in food presentation in general led to decreased drinking, which recovered when the signaled delays were discontinued. The drinking of yoked-control rats, which received food at the same times as those exposed to the signaled-delay contingency, showed much smaller changes. Experiment 2 showed that 10-s lick-dependent signals alone did not reduce drinking. In Experiment 3, when licks produced unsignaled 10-s delays in food there were less marked and more gradual changes in drinking than in Experiment 1, although these effects again were greater than with yoked-control animals. We concluded that both signaled and unsignaled delays functioned as punishers of drinking. These findings support the view that schedule-induced drinking, like operant behavior, is subject to control by its consequences.     

Sequential effects of interval duration on fixed-interval performance

The bar pressing of rats was reinforced on a multiple fixed-interval schedule. The schedule intervals were 1 and 5 min long, and the sequence was such that intervals of either duration were equally likely to be followed by intervals of the same or of the other duration. Rates were higher during 1-min and after 5-min intervals. Best fit equations for cumulative responses during the 5-min intervals produced very similar exponents regardless of preceding duration. It was concluded that preceding duration may have affected the subjects' performances through direct effects on temporal discrimination.     

Within-session meal-size effects on induced drinking.

As a control for the effects of session duration and hunger on the relation between food magnitude and induced drinking, four food-deprived rats were exposed to a variable-time 50-s schedule of food delivery in which the size of each food delivery varied randomly within sessions. Food-related behavior and schedule-induced drinking per opportunity were examined as functions of meal size and postfood time. All rats showed an inverted-U-shaped relation between drinking per opportunity and meal size. This relation was caused by variation in the percentage of intervals that contained drinking and by variation in the number of drinking bouts per interval, rather than by bout duration or by the amount of drinking within those intervals that actually contained drinking. Head-in-feeder time increased linearly with meal size. Schedule-induced drinking was entrained by food delivery in 3 of 4 subjects; the entrainment was due to regulation of the starting time of each drinking bout rather than to regulation of bout duration.     

Choice behavior of rats in a concurrent-chains schedule: Amount and delay of reinforcement

Rats were exposed to concurrent-chains schedules in which the terminal links were equal fixed-interval schedules terminating in one or three food pellets. Choice proportions for large reward increased with increases in delay intervals programmed on fixed-interval schedules and supported the predictions derived from a general choice model originally formulated by Fantino and later developed by Navarick and Fantino. In addition, a functional equivalence of two alternatives was established by increasing delay intervals with large reward, whereas delay intervals for small reward were held constant. Functionally equivalent delay intervals with large reward, for each delay interval with small reward, can be described by a power function with exponent smaller than 1.0. A better prediction of choice proportions resulted when this function was used to derive predicted choice proportions.     

Acquisition and maintenance of postshock response pattern in nondiscriminated avoidance with rats

Five experimentally naive albino rats were placed under a nondiscriminated lever-press avoidance schedule in which the delay to the next shock for responses after a shock was longer than the delay for responses after a response. Four rats acquired the postshock response pattern and maintained it for a prolonged period. The results revealed that postshock responding was under operant control and was not purely shock-elicited. It was suggested that the two kinds of response-shock interval, i.e. the shock-response-shock interval and the response-response-shock interval, could and should be independently controlled in nondiscriminated avoidance schedules.     

Lick-trading by rats: on the substitutability of dry, water, and saccharin tubes.

Thirsty rats licked two metal tubes: a water tube paired with another water tube, with saccharin, or with a dry tube. For each pair, a multipoint baseline function was measured by offering free access to one tube throughout each session, and free or restricted access to the other. The three resulting baseline functions showed the members of each pair to be mutual substitutes: When access to either tube was restricted, the rats made more licks at the other. A linear function identified the two water tubes as perfect substitutes. Convex functions identified the members of the saccharin-water and the dry-water pair as imperfect substitutes. Each pair was also tested under several reciprocal fixed-ratio schedules that required instrumental licking of either tube for contingent access to the other. The resulting schedule functions showed the members of each pair to be perfect substitutes: Water licks decreased linearly as licks at the other water tube, the saccharin, or the dry tube increased, in agreement with a conservation model of instrumental performance. Baseline and schedule functions, indistinguishable in the water-water pair, indicated a schedule facilitation of dry-tube licking in the dry-water pair and of water-tube licking in the saccharin-water pair.     

Some parameters of behavioral contrast and allocation of interim behavior in rats

Two experiments examined the effects of baseline reinforcement rate and component duration on behavioral contrast and on re-allocation of interim behavior in rats. Positive behavioral contrast occurred during multiple variable-interval 10-second extinction (VI 10 EXT) after a multiple VI 10 VI 10 baseline condition, but not during multiple VI 60 EXT following multiple VI 60 VI 60 baseline. Component duration had no significant effect on contrast. These results differed from those found in studies of pigeons' key pecking. Contrast was accompanied by an increased rate of drinking in the changed component, but drinking in the constant component did not decrease. These results are not consistent with the competition theory of contrast, but are consistent with the predictions based on the matching law. However, no current theory seems to account for all instances of behavioral contrast.     

Response–reinforcer contiguity versus response-rate–reinforcer-rate covariance in rats' lever pressing: Support for a multiscale view

The multiscale molar view sees behavior as a flow, like a river, extended in time. Matching theory expresses the way activities compete for time. Relative time taken by any activity depends on relative induction. The present experiment tested matching theory applied to concurrent contingent and noncontingent food. As adjunctive activities that compete with operant activity, we recorded hopper head entries and presses on a lever near the food hopper that had no programmed consequences. Eight naïve rats were first exposed to a variable-time 60 s schedule, which across conditions was gradually transformed into a variable-interval 60 s schedule by increasing the proportion of food that was delivered contingent on pressing a lever far from the hopper. Another group of 4 rats that had been trained to press a lever near a food hopper were introduced in the second condition, in which one food delivery was contingent on far-lever pressing. We found induction following a power function to describe pressing on the far lever (operant activity). Matching theory combined with power-function induction also accounted for adjunctive activity. Results with single contingent food deliveries provided little support for the molecular view that behavior consists of discrete responses “strengthened” by immediately following reinforcers.     

Response–reinforcer dependency and resistance to change

The effects of the response–reinforcer dependency on resistance to change were studied in three experiments with rats. In Experiment 1, lever pressing produced reinforcers at similar rates after variable interreinforcer intervals in each component of a two‐component multiple schedule. Across conditions, in the fixed component, all reinforcers were response‐dependent; in the alternative component, the percentage of response‐dependent reinforcers was 100, 50 (i.e., 50% response‐dependent and 50% response‐independent) or 10% (i.e., 10% response‐dependent and 90% response‐independent). Resistance to extinction was greater in the alternative than in the fixed component when the dependency in the former was 10%, but was similar between components when this dependency was 100 or 50%. In Experiment 2, a three‐component multiple schedule was used. The dependency was 100% in one component and 10% in the other two. The 10% components differed on how reinforcers were programmed. In one component, as in Experiment 1, a reinforcer had to be collected before the scheduling of other response‐dependent or independent reinforcers. In the other component, response‐dependent and ‐independent reinforcers were programmed by superimposing a variable‐time schedule on an independent variable‐interval schedule. Regardless of the procedure used to program the dependency, resistance to extinction was greater in the 10% components than in the 100% component. These results were replicated in Experiment 3 in which, instead of extinction, VT schedules replaced the baseline schedules in each multiple‐schedule component during the test. We argue that the relative change in dependency from Baseline to Test, which is greater when baseline dependencies are high rather than low, could account for the differential resistance to change in the present experiments. The inconsistencies in results across the present and previous experiments suggest that the effects of dependency on resistance to change are not well understood. Additional systematic analyses are important to further understand the effects of the response–reinforcer relation on resistance to change and to the development of a more comprehensive theory of behavioral persistence.     

Rat choice in rapidly changing concurrent schedules

In two experiments, experimentally naïve rats were trained in concurrent variable‐interval schedules in which the reinforcer ratios changed daily according to a pseudorandom binary sequence. In Experiment 1, relative response rates showed clear sensitivity to current‐session reinforcer ratios, but not to previous sessions' reinforcer ratios. Within sessions, sensitivity to the current session's reinforcement rates increased steadily, and by session end, response ratios approached matching to the current‐session reinforcer ratios. Across sessions, sensitivity to the current session's reinforcer ratio decreased with continued exposure to the pseudorandom binary sequence, contrary to expectations based on previous studies demonstrating learning sets. Using a second group of naïve rats, Experiment 2 replicated the main results from Experiment 1 and showed that although there were increases over sessions in both changeover rate and response rate during the changeover delay, neither could explain the accompanying reductions in sensitivity. We consider the role of reinforcement history, showing that our results can be simulated using two separate representations, one local and one nonlocal, but a more complex approach will be needed to bring together these results and other history effects such as learning sets and spontaneous recovery.