Effects of expectancies of different reward magnitudes in transfer from noncontingent pairings to instrumental performance

In two experiments, rats received noncontingent pairings of two stimuli with food reward, one paired with small reward and the other with large reward, and received bar press training with large reward or with small reward. When the noncontingent stimuli (NS) were presented for test during subsequent rewarded bar pressing and during early extinction of bar pressing, responding for each group was faster in the presence of the NS which was paired with the same reward magnitude that group received in bar press training than to the NS which had been paired with a different reward magnitude. As extinction progressed, all groups responded more slowly in the presence of the NS which had been paired with the large reward than in the presence of the NS which had been paired with small reward. These results were interpreted as indicating that responding in the presence of an NS depends on: (i) whether the reward expectancy elicited by the NS has been conditioned to the instrumental response, and (ii) the relationship between the reward expected in the presence of the NS and that received in test.     

Transfer from discrimination under hunger to discrimination under thirst: The role of expectancy and habit

The experimental group (Group HA-TA) received food (F) and water (W) rewarded trials in an alternating sequence under hunger in Phase 1 and under thirst in Phase 2. Group HA-TA ran faster on F than on W trials in Phase 1, and faster on W than on F trials in Phase 2. Early in Phase 2 the difference between speeds on W and F trials was larger for Group HA-TA than for a group which received no runway training in Phase 1 (Group HO-TA), but later in Phase 2 this difference was larger for Group HO-TA than for Group HA-TA. Also in Phase 2 the difference between speeds on W and F trials was larger for Group HA-TA than for a group which received a random sequence of F and W trials under hunger in Phase 1, and smaller for Group HA-TA than for a group which received alternating F and W trials under thirst in both phases. To interpret these results it was assumed that for Group HA-TA the expectancies of reward formed in Phase 1 facilitated development of alternation performance in Phase 2, but that the S-R associative connections formed in Phase 1 inhibited ultimate development of alternation performance in Phase 2.     

Reversal learning as a function of changed reward location or changed drive

In two experiments, rats were trained with food in one location (e.g., black alley) and water in another location (white alley) under hunger or thirst. Subsequently, either the locations of the rewards were reversed, or the drive was changed (from hunger to thirst or thirst to hunger). Reversal of instrumental responses took considerably longer when drive was changed and rewards remained in the same locations than when reward locations were reversed. These results were interpreted as indicating that the animal's internal representations of the rewards received in each location transfer when drive is changed. These internal-reward representations interfere with reversal learning by eliciting the responses which were conditioned to them in Phase 1. Because the values of food and water reverse when drive is changed from hunger to thirst or vice versa, it was suggested that the reward representations surviving the drive shift are cognitive representations of the specific events received (food or water), independent of the value of the rewards under either hunger or thirst.     

Shock preexposure and the reduced effectiveness of shock

In three experiments experience with shock was shown to reduce the effectiveness of shock as a reinforcer or motivator. In Experiment 1 rats were given signaled shock in a box separate from the runway where they were subsequently punished. These rats were less suppressed by shock punishment than rats that had no previous shock experience. In Experiment 2 preshocked rats were less suppressed by punishment and were slower to learn an escape-avoidance response than nonpreshocked rats, whether the preshock was signaled or unsignaled. In Experiment 3 as number of CS-shock pairings increased, fear of the CS decreased as did fear of the context. These results suggest that some central adaptation process produced by experience with shock reduces the effectiveness of shock as a reinforcer whenever shock is used repeatedly. This is independent of other effects, such as context blocking, that can affect responding after shock preexposure.     

Resistance to satiation: Reinforcing effects of food and eating under satiation

It has been shown previously that rats which have learned a response when hungry will continue to make that response when tested satiated, a phenomenon labeled resistance to satiation. Here we showed that rats which were previously trained hungry will learn a new response for the opportunity to consume pellets in a new situation when tested satiated. In four experiments various groups received each of the components of the training given when rats learn an instrumental response when hungry. Rats were placed in the goalbox of a straight alley and given food pellets when hungry or were hungry only in their home cages prior to running a straight alley in the satiated test in Experiment 1. In Experiments 2, 3, and 4 learning of a differential conditioning problem for pellets in S+ (nonreward in S?) was measured in the satiated test. Groups given pellets in their home cages when hungry with or without alley exposure learned to run more rapidly in S+ than in S? in the satiated test phase. The tendency to eat pellets in the apparatus and the reinforcing effect of eating the pellets was larger for rats which ate the pellets when hungry in their home cage than for rats which ate the pellets when satiated in their home cage. Being hungry in the home cage with no pellets was not sufficient to produce eating or running for pellets in the satiated test, indicating that any inherent reinforcing effect of the pellets is not sufficient to produce eating or running, and that incomplete satiation cannot account for the learning. These data indicate that a reinforcing effect of eating pellets under satiation is an important determiner of resistance to satiation.     

Percentage body weight and the successive negative contrast effect in rats

In two runway experiments employing rats the successive negative contrast effect was evaluated for animals maintained at high or low body weights. In both experiments the effects on performance of shifting reward magnitude were independent of body weight. These results contrast with those of previous studies in which the successive negative contrast effect occurred only under low body weight. It was suggested that when conditions are maximal or near maximal for production of the successive negative contrast effect, as they were here but not in previous investigations, body weight will not influence the size of this effect.     

Reward schedule effects in extinction: Intertrial interval, memory, and memory retrieval

Rats were trained in a runway such that partial reward occurred on Trial 1 of the day and consistent reward on subsequent massed trials (Group PRT1), or consistent reward occurred on Trial 1 of the day and partial reward on subsequent massed trials (Group PRTM). Under spaced (24-hr) extinction, Group PRT1 was more resistant to extinction than Group PRTM and under massed (1-min) extinction, Group PRTM was more resistant to extinction than Group PRT1. These findings suggest that (a) distinctive stimuli are associated with Trial 1 of the day and with subsequent massed trials, (b) these distinctive stimuli function as retrieval cues for memories, memory retrieval being independent of intertrial interval, and (c) behavior in extinction is controlled by a stimulus compound consisting of the memory of nonreward plus stimuli which accompany the memory of nonreward on rewarded acquisition trials.     

Partial reward training level and reward magnitude: Effects on acquisition and extinction

Two groups of 10 rats each received either a large magnitude (0.90 g) or a small magnitude (0.18 g) of partial reward (PR) and seven successive acquisition-extinction sessions in the runway. The large magnitude PR group ran much faster than the small magnitude PR group in the early acquisition sessions with differences between the groups declining over sessions. In the early extinction sessions, the large magnitude PR group showed greater resistance to extinction than the small magnitude PR group, but in the late extinction sessions this relation reversed itself. Finally, resistance to extinction decreased over sessions, this decrease being greater under a large than under a small magnitude of PR.     

Deprivation and reward stimuli as compound stimuli

In Experiment 1 the experimental group was tested with a deprivation level and a reward magnitude which it had experienced previously but which it had not experienced in combination. This group was inferior in test performance to a group which had experienced the test deprivation-reward combination prior to test. These results were interpreted as indicating that deprivation stimuli and reward stimuli form a compound stimulus and training on the elements of the compound produces performance inferior to training directly on the compound. In Experiment 2, the decrement associated with two different shifts in deprivation and reward did not differ despite the different size change of total incentive involved in the two shifts. The results were interpreted as indicating that the deprivation-reward stimulus is not produced by a single underlying incentive mechanism.     

Resistance to satiation of consummatory and instrumental performance

In three experiments rats received training in a straight alley under high hunger and then were tested satiated. Both eating and running continued to occur under satiation, but the two responses were not completely correlated, and continued running did not depend upon continued eating. Further, groups differed in their eating behavior, although all experienced the same satiation procedure, suggesting that eating under satiation is not just a reflection of incomplete satiation. Resistance to satiation of the running response was greater following partial reward than following consistant reward and tended to be greater following small reward training than large reward training, regardless of schedule of reward. Eating during satiation was greater following partial than following consistent reward and was greater if the same reward magnitude was given in satiation as in acquisition than if a different reward magnitude was given. It was suggested that resistance to satiation is an associative phenomenon. Eating and running occur during satiation because the stimuli present during satiation continue to elicit them. The differences between results using rewarded satiation and results using high drive extinction as measures of persistence were attributed to satiation being nonfrustrating.