Fixed-ratio schedules increase generalized self-control: Preference for large rewards despite high effort or punishment.

Three experiments investigated the effects of FR reinforcement on generalized self-control involving high effort and punishment. In Experiment 1, rats received food in a runway for the completion of each round trip (continuous-reinforcement group) or every fifth round trip (FR group). Control rats received food at the same temporal intervals as these groups but without any instrumental requirement. When all rats were next given a series of choices between a large food reward requiring high lever force versus a small reward requiring low lever force, the FR rats showed the greatest self-control. In Experiments 2 and 3, rats were rewarded on a continuous or FR schedule followed by choice between a large food reward accompanied by intermittent shock vs a small or absent food reward without shock. The FR rats again showed the greatest self-control. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Incentive shifts in the goldfish.

Trained 157 goldfish with a large or small magnitude of reward in a straight-alley runway. After 20 days of training with a given reward magnitude, 1/2 of the Ss in each group were shifted to the other magnitude of reward. Ss rapidly shifted swimming speeds when reward magnitudes were reversed. No contrast effects were observed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some effects of single alternation training of rats in a double runway.

Gave independent groups of male hooded rats (n = 30) either (a) single alternation (SA) of reward and nonreward in the 1st goal box of a double runway and 100% reward in the 2nd goal box, (b) concurrent SA in both goal boxes, (c) SA in the 1st goal box and no experience in the 2nd runway, or (d) random 50% reward in the 1st goal box accompanied by 100% reward in the 2nd goal box. SA training in the 1st or in both segments of the double runway yielded reliable SA patterning wherever such training occurred. Concurrent SA training in both segments yielded the fastest development of patterning. "Frustration effects" in the 2nd runway were consistently greater following SA in the 1st goal box than following random reward and nonreward. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of daily reward sequences on S- discrimination contrasts in rats.

Conducted 3 experiments to examine the role of within-day sequences of large (L) and small (S) reward in S- negative contrast effects (NCEs) in differential conditioning of naive albino rats. Exp. I demonstrated an NCE for 2 groups receiving LLSS or LSSL sequences, respectively, but not for an SSLL group. Correlated startboxes were used as prestart cues. Exp. II used 2 trials/day in regular and irregular sequences, and demonstrated the necessity of at least occasional L-S transitions in producing an S- NCE. Exp. III supported these findings using 3 trials/day. These combined results are interpreted as requiring a revision of extant notions of expectancy. (17 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age of first appearance of simultaneous and successive negative contrast in infant rats.

Simultaneous (SimNC) and successive (SNC) negative contrast, 2 paradoxical effects that are related to shifts in reward magnitude, were studied in 148 rat pups. In Exps I and II, 11-, 14-, and 17-day-old Ss were able to discriminate between the large (milk suckling) and small (dry suckling) reward odor cues as measured by attachment latencies, but only the 14- and 17-day-olds showed SimNC. At none of the 3 ages was a discrimination formed to the differential odor cues in the alley in terms of runway speeds. In Exp III, Ss were placed directly on the dam's ventrum to facilitate attachment. As in the earlier experiment, the 11-day-olds discriminated between the odors signaling the 2 reward conditions but did not show the SimNC effect. In Exp IV, SNC was shown at 17 days but not at 14 days in the attachment latency measure and at neither age in the run measure. These 4 experiments extend earlier findings that the paradoxical effects that emerge out of intermittent schedules of reward magnitude occur earlier than those associated with single abrupt shifts in reward magnitude. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of varied preshift reward magnitude on successive negative contrast effects in rats.

A total of 110 male Sprague-Dawley albino rats, distributed across 3 experiments, received simple instrumental conditioning trials in a straight runway. In each experiment the conditions of reward prior to a shift to small reward were varied between groups. Collectively, results indicate that the extent of the negative contrast effect depends upon the difference between pre- and postshift incentive levels and that Ss exposed to varied reward magnitude training average the incentive values of these rewards. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Arousal of frustration following gradual reductions in reward magnitude in rats.

16 male Holtzman rats were assigned to each of 4 groups; Ss were given a 14-pellet reward for 60 runway acquisition trials. During a subsequent 18-trial shift phase, one group was shifted to a 1-pellet reward on Trial 1, a 2nd was shifted on Trial 13, and a 3rd was given 1 less pellet each trial and then 1 pellet for the last 6 trials. The speeds of all 3 groups decreased to a level below that of a control group given a 1-pellet reward throughout training. All Ss were then given hurdle-jump training to escape from the 1-pellet reward to a neutral box. All 3 shifted groups showed acquisition of the response, whereas the control group did not. Results indicate that both gradual and abrupt reward reductions arouse frustration. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Generalized self-control of delay and effort.

Studied the effects of delayed reward and rewarded effort on subsequent generalized self-control involving delay and effort in 88 2nd and 3rd graders. Different groups of Ss received immediate reward or delayed reward for low effort or for high effort on a combination of tasks that involved object counting, picture memory, and shape matching. Self-control involving delay was measured by providing the Ss with choices between waiting for a large reward vs receiving a small reward without waiting, and self-control involving effort was measured by means of choices between copying nonsense words for a large reward vs receiving a small reward without copying. Delayed reward increased subsequent self-control involving delay without affecting self-control of effort. Rewarded high effort increased subsequent self-control involving effort without affecting self-control of delay. Results suggest that (a) adaptation to delay reduces its aversiveness and (b) the degree of effort sustained in rewarded tasks becomes learned and generalizes across behaviors. It is concluded that the generalized effects of delayed reward and rewarded high effort may contribute to individual differences in the willingness to postpone gratification in pursuit of long-term goals. (72 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Observing response acquisition: Preference for unpredictable appetitive rewards obtained under conditions predicted by DMOD.

To investigate the preference for unpredictable rewards predicted by the present author and J. T. Daly's (see record 1983-20275-001) modification, known as the DMOD model, of R. A. Rescorla and A. R. Wagner's (1972) previous model of reinforcement, the present author conducted 5 E-maze experiments with 144 male Holtzman rats. In Exps I–V, Ss were given a choice between receiving reward and nonreward in a situation in which stimuli were correlated with reward outcome (predictable situation) vs a situation in which the stimuli were uncorrelated with reward outcome (unpredictable situation). Preference for the unpredictable situation occurred under the following conditions: small (1 37-mg pellet) immediate rewards, small delayed (15-sec) rewards when the cues correlated with reward outcome were absent during the delay interval, large (15 pellets) immediate rewards when a difficult discrimination was required, and when the stimulus predicting nonreward was present at the choice point. Preference for the predictable situation was strongest if reinforcement was delayed and large or if the stimulus predicting reward was present at the choice point. A weaker preference for the predictable situation occurred if reinforcement was immediate, large, and required a simple discrimination or if reinforcement was large and delayed and the cues that correlated with reward outcome were absent during the delay interval. Findings support the predictions of the DMOD model of appetitive learning. (33 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Selective breeding for negative contrast in consummatory behavior.

Rats showing either large or small reductions in licking following a shift from 32% to 4% sucrose were selectively bred for 7 generations. Rats from the 2 resulting lines reliably differed in successive negative contrast and in activity (radial-arm maze and open field). Differences in activity and contrast were not correlated. Heritability (h–2) of the reaction to sucrose shift was reliable in the last 6 filial generations and equaled 0.64 in the F? generation. The 2 lines did not differ (1) in response to the absolute rewarding value of sucrose or cocaine; (2) in open-field defecations or thigmotaxis; (3) in anticipatory contrast; or (4) in responsivity to midazolam. Responsivity to reward reduction may involve a relatively delimited psychological process that is amenable to selection. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cooperative task-oriented groups in a college classroom: A field application.

A large college class with 84 students was restructured into small task-oriented groups either randomly or by sociometric choice. Under individual reward conditions, sociometric groups were more likely than random groups to function outside the classroom; under shared reward conditions, both types of groups were equally viable. Working in groups did not affect subsequent individual test performance; however, on a joint project, teamwork resulted in better performance than individual efforts. The overall ability of students to cope with the course was not affected by group participation. A subgroup of students who performed poorly on the 1st individual task subsequently worked in groups and performed significantly better on a 2nd individual task than comparable students who did not participate in groups during the course. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Can salient reward increase creative performance without reducing intrinsic creative interest?

Two experiments, involving 416 preadolescent school children, investigated the effects of monetary reward on generalized creative performance and intrinsic creative interest. In Experiment 1, the explicit requirement of novel performance in 1 task (generating unusual uses for physical objects) produced greater subsequent creative performance in an entirely different task (picture drawing) when a large reward was used rather than a small reward or no reward. In Experiment 2, reward for novel performance increased subsequent intrinsic creative interest, measured here by the choice to produce original drawings rather than copy a familiar drawing. Intrinsic creative interest was reduced only by reward for uncreative performance. These findings suggest that the explicit requirement of novel performance for salient reward enhances generalized creativity without any loss of intrinsic creative interest. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The role of the nucleus accumbens core in impulsive choice, timing, and reward processing.

The present series of experiments aimed to pinpoint the source of nucleus accumbens core (AcbC) effects on delay discounting. Rats were trained with an impulsive choice procedure between an adjusting smaller sooner reward and a fixed larger later reward. The AcbC-lesioned rats produced appropriate choice behavior when the reward magnitude was equal. An increase in reward magnitude resulted in a failure to increase preference for the larger later reward in the AcbC-lesioned rats, whereas a decrease in the larger later reward duration resulted in normal alterations in choice behavior in AcbC-lesioned rats. Subsequent experiments with a peak timing (Experiments 2 and 3) and a behavioral contrast (Experiment 4) indicated that the AcbC-lesioned rats suffered from decreased incentive motivation during changes in reward magnitude (Experiments 2 and 4) and when expected rewards were omitted (Experiments 2 and 3), but displayed intact anticipatory timing of reward delays (Experiments 2 and 3). The results indicate that the nucleus accumbens core is critical for determining the incentive value of rewards, but does not participate in the timing of reward delays. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reward magnitude in differential conditioning: Effects of sequential variables in acquisition and extinction.

Nine Sprague-Dawley male albino rats were randomly assigned to each of 5 groups. Three groups received differential conditioning to small (S) and large (L) reward. One group (LS) experienced L–S transitions, a 2nd group (SL) experienced S–L transitions, and a 3rd group (LS–SL) received the combined sequences of Groups LS and SL. Two control groups received only L or S trials. Negative contrast (slower speeds in the S-alley than the S control group had) was demonstrated for all 3 differential groups, and positive contrast (faster speeds in the L-alley than the L control group had) was demonstrated in Groups LS and SL, but not LS–SL. In extinction, Groups S and L showed the usual between-S differences in resistance to extinction (S more resistant than L); Groups LS and LS–SL also showed this effect, based on the within-S procedure. Group SL showed the opposite effect, which was predicted by an extension of the sequential hypothesis of extinction effects. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reward magnitude and partial reinforcement effects in a single runway.

The partial reinforcement acquisition effect (PRAE) in running speeds and the frustration effect (activity following nonreward compared with reward) were measured simultaneously in an alley whose goal-box floor was a stabilimeter. Experimental groups of 9 male Charles River albino rats each received 50 or 100% reinforcement combined factorially with 3 magnitudes of reward (1, 3, or 9 pellets). A control group of 18 Ss was never rewarded. The size of the PRAE was a direct function of reward magnitude, and crossing of 50 and 100% curves was found for all alley segments, including the goal segment. The frustration effect (FE) was present by the 2nd day of training for the 3- and 9-pellet groups, and the size of the FE was directly related to reward magnitude. The present study is unique in that (a) the findings were free from the effects of reward contrast, (b) behavior antecedent to the goal indicated that incentive was effectively manipulated, and (c) an unrewarded control group was used. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Object permanence in orangutans (Pongo pygmaeus), chimpanzees (Pan troglodytes), and children (Homo sapiens).

Juvenile and adult orangutans (n?=?5; Pongo pygmaeus), chimpanzees (n?=?7; Pan troglodytes), and 19- and 26-month-old children (n?=?24; Homo sapiens) received visible and invisible displacements. Three containers were presented forming a straight line, and a small box was used to displace a reward under them. Subjects received 3 types of displacement: single (the box visited 1 container), double adjacent (the box visited 2 contiguous containers), and double nonadjacent (the box visited 2 noncontiguous containers). All species performed at comparable levels, solving all problems except the invisible nonadjacent displacements. Visible displacements were easier than invisible, and single were easier than double displacements. In a 2nd experiment, subjects saw the baiting of either 2 adjacent or 2 nonadjacent containers with no displacements. All species selected the empty container more often when the baited containers were nonadjacent than when they were adjacent. It is hypothesized that a response bias and inhibition problem were responsible for the poor performance in nonadjacent displacements. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The hippocampus and conditioning to contextual cues.

Two experiments are reported in which behavioral control by contextual cues was assessed in groups of rats with dorsal hippocampal (HC), neocortical (NC), or operated control (OC) lesions. Following Odling-Smee's (1975) procedure, a Pavlovian conditioning paradigm was followed in which conditioned stimuli (CS; tone, light) predicted an unconditioned stimulus (US; footshock) always, never, or half the time. Conditioning trials took place in a small black box. Subsequently, conditioning to background contextual cues was assessed by measuring the amount of time rats spent in the black box in preference to an adjacent white one with neither CS nor US presented. In OC groups and, to a lesser extent, NC groups, conditioning to background cues was inversely related to the probability that CS predicted US. In contrast to graded contextual conditioning in control groups, the HC groups consistently showed abnormally strong conditioning to context that was at or near asymptotic level. The results, which were related to current theories of the relation between contextual stimuli and CS, suggest that the hippocampus may play an important role in stimulus selection during learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of cytotoxic lesions of the hippocampus on recognition memory in the rat: Effects of stimulus size.

Rats with excitotoxic hippocampal lesions were trained on delayed nonmatching-to-sample (DNMS) with small goal boxes, containing complex objects, presented on a pseudo trial-unique schedule. A series of experiments then tested performance on repeated presentation of either the small object or large empty goal boxes. All rats acquired the nonmatching rule, but hippocampal-lesioned rats performed less well than controls on choice accuracy for the final 2 blocks of acquisition. In the study's main phase, the lesions impaired choice accuracy when the large empty boxes were used as stimuli. This deficit was ameliorated when the rats were tested with the small object boxes, although the performance of the hippocampal-lesioned rats was still below that of controls. These results extend previous reports of box size-dependent effects of hippocampal aspiration lesions on DNMS and suggest that selective damage to the hippocampus, not neuronal loss in adjacent structures or fiber tracts, is critical for the effect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dynamics of mismatch correction in the hippocampal ensemble code for space: interaction between path integration and environmental cues

Populations of hippocampal neurons were recorded simultaneously in rats shuttling on a track between a fixed reward site at one end and a movable reward site, mounted in a sliding box, at the opposite end. While the rat ran toward the fixed site, the box was moved. The rat returned to the box in its new position. On the initial part of all journeys, cells fired at fixed distances from the origin, whereas on the final part, cells fired at fixed distances from the destination. Thus, on outward journeys from the box, with the box behind the rat, the position representation must have been updated by path integration. Farther along the journey, the place field map became aligned on the basis of external stimuli. The spatial representation was quantified in terms of population vectors. During shortened journeys, the vector shifted from an alignment with the origin to an alignment with the destination. The dynamics depended on the degree of mismatch with respect to the full-length journey. For small mismatches, the vector moved smoothly through intervening coordinates until the mismatch was corrected. For large mismatches, it jumped abruptly to the new coordinate. Thus, when mismatches occur, path integration and external cues interact competitively to control place-cell firing. When the same box was used in a different environment, it controlled the alignment of a different set of place cells. These data suggest that although map alignment can be controlled by landmarks, hippocampal neurons do not explicitly represent objects or events.     

Midazolam administered to rats induces anterograde amnesia for changes in reward magnitude.

L. P. Crespi (1942) showed that rats trained to run an alley for a large food reward slowed down when shifted to a small reward. This effect is usually interpreted as an aversive emotional response to reward reduction (A. Amsel, 1958). Benzodiazepines attenuate the behavioral effects of reward reduction (C. F. Flaherty, 1990), but the emphasis has been on their anxiolytic, not memory-impairing, effects. Researchers trained rats (175–200 g) to run an alley for food until asymptote was reached. Reward magnitude was then either decreased (Experiment 1) or increased (Experiment 2). The benzodiazepine midazolam (1 mg/kg ip), injected immediately prior to a decrease or increase in reward magnitude, impaired the later retention of both changes in a manner consistent with anterograde amnesia. The findings suggest that the memory-impairing effects of benzodiazepines may, at least in part, influence the response to reward reduction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)