Saturation of subjective reward magnitude as a function of current and pulse frequency.

In 6 rats with electrodes in the medial forebrain bundle, the upper portion of the function relating the experienced magnitude of the reward to pulse frequency was determined at currents ranging from 100 to 1,000 μA. The pulse frequency required to produce an asymptotic level of reward was inversely proportional to current except at the lowest currents and highest pulse frequencies. At a given current, the subjective reward magnitude functions decelerated to an asymptote over an interval in which the pulse frequency doubled or tripled. The asymptotic level of reward was approximately constant for currents between 200 and 1,000 μA but declined substantially at currents at or below 100 μA and pulse frequencies at or above 250 to 400 pulses per second. Results are consistent with the hypothesis that the magnitude of the experienced reward depends only on the number of action potentials generated by the train of pulses in the bundle of reward-relevant axons. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effectiveness of learned reinforcement as a function of primary reward percentage and number of primary pairings.

136 male albino rats were trained while water-deprived to lever-press for water reinforcement. Then, with the lever retracted and while food-deprived, different groups were administered either 40, 80, 160, or 320 pairings of a neutral stimulus (sN)compound, light and feeder "click," with primary reinforcement (sR). The 45-mg reward was presented on either a 25, 50, or 100% schedule. The design was thus a 3 * 4 factorial. Control groups which received no pairings (N = 10) or 80 nonreinforced presentations of the sN (N = 6) were included. During testing, with the lever inserted, the light and "click" compound followed each lever-pressing response. Results indicate that effectiveness of secondary reinforcement was an inverted U shaped function of percentage of sR, and an over-all increasing linear function of number of sN sR pairings. (French summary) (17 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spaced-trials reward magnitude effects in the rat: Single versus multiple food pellets.

Trained 56 male Charles River hooded rats in a runway with either small- or large-reward magnitude. Both small and large rewards were presented in single- or multiple-pellet form. 1 training trial was given each day for 120 days. Early in training, the large-reward Ss ran faster than those receiving small reward, and the effect was more pronounced in the multiple-pellet condition. Later in training, the small-reward Ss equaled the performance of Ss receiving large reward and even ran somewhat faster in the run section of the alley. The typical extinction effect of greater persistence for small-reward Ss was observed, but only in the goal section. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Self-stimulating rats combine subjective reward magnitude and subjective reward rate multiplicatively.

For rats that bar pressed for intracranial electrical stimulation in a 2-lever matching paradigm with concurrent variable interval schedules of reward, the authors found that the time allocation ratio is based on a multiplicative combination of the ratio of subjective reward magnitudes and the ratio of the rates of reward. Multiplicative combining was observed in a range covering approximately 2 orders of magnitude in the ratio of the rates of reward (from about 1:10 to 10:1) and an order of magnitude change in the size of rewards. After determining the relation between the pulse frequency of stimulation and subjective reward magnitude, the authors were able to predict from knowledge of the subjective magnitudes of the rewards and the obtained relative rates of reward the subject's time allocation ratio over a range in which it varied by more than 3 orders of magnitude. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Species generality of within-subjects reward magnitude effects.

12 female pigtail, stumptail, and squirrel monkeys and 4 female Holtzman albino rats were given acquisition, extinction, and reacquisition training in a discrete-trials 2-lever spatial discrimination situation. In acquisition the left and right levers were associated with 5- and 1-pellet rewards, respectively, and in reacquisition, response to either lever produced 5-pellet reward. The 4 species showed similar patterns of preference for the 5-pellet lever on 2-lever choice trials and differential responding on 1-lever forced trials in acquisition, and similar within-Ss extinction effects which were at variance with the typical crossover of large- and small-reward extinction curves in between-groups reward magnitude studies with rats. Species differences appeared in over-all relative rate of extinction, with the macaques showing the fastest extinction, and in the degree to which historical effects of acquisition conditions appeared and persisted in reacquisition. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Growth of brain stimulation reward as a function of duration and stimulation strength.

The strength of a train of rewarding brain stimulation required to support a criterion level of operant performance declines hyperbolically as the duration is increased. This finding has been attributed to a process of leaky integration. However, the rate at which integration approaches asymptote has been shown to depend on stimulation strength, a finding that differs from the behavior of a simple leaky integrator. The authors replicate both findings and show that they are both well described by a new model that incorporates a hyperbolic strength-duration function, a logistic function mapping stimulation frequency onto reward intensity, and another logistic function mapping reward intensity onto performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The pedunculopontine tegmental nucleus and responding for sucrose reward.

Pedunculopontine tegmental nucleus (PPTg) lesions in rodents lead to increased sucrose consumption, but the psychological deficit behind this remains uncertain. To understand better the relationship between consumption of, and motivation for, sucrose, the authors trained rats to traverse a runway for 20% or 4% sucrose solution; after 7 days, concentrations were reversed. Control rats consumed more 20% than 4% sucrose solution and promptly altered run times in response to concentration change. PPTg-lesioned rats consumed normal quantities of 4% but more 20% sucrose solution than controls and took longer to alter their runway time following the concentration change. These data suggest that lesions of the PPTg do not alter motivation per se and might be better understood as inducing a response selection deficit. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preference for alcohol consumption as a function of amount and delay of alternative reward.

Sixty male normal drinkers were placed in a choice situation with two behavioral alternatives; one produced access to alcohol consumption, and one produced access to opportunities to win money on a probabilistic dice throw task. Any alcohol chosen was available during the session, and constraints on access to it were held constant. Two independent variables involving constraints on access to money were manipulated in a 2?×?3 factorial design: (a) amount of money available, which was determined by the probability of a "win" on the dice throw task (either .17 or .83), and (b) delay in receipt of any money won (either no delay, a 2-week delay, or an 8-week delay). The main dependent measures were the proportion of responses allocated to gain access to alcohol, response-outcome expectancies, and mood state. Subjects' preferences for alcohol varied positively with delay but were not significantly influenced by the money-amount manipulation. Subjects' choice behavior was not related to mood states or expectations. The results partially replicate those of an earlier experiment and lend credence to a formulation of the determinants of drinking behavior based on behavioral theories of choice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Extinction of avoidance in rats as a function of duration and number of blocked trials.

Gave 15 groups of 8 Sprague-Dawley rats each avoidance training in a runway. Each S was then blocked in the presence of the CS for either 1, 5, or 12 trials, each lasting for either 0, 5, 10, 50, or 120 sec. Results indicate that the greater the number of blocked trials and the greater the length of each blocked trial, the less the resistance to extinction. The key variable in determing the resistance to extinction was total blocking time as opposed to either the number of blocked trials or length of each blocked trial. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Runway performance of rats for brain-stimulation or food reward: Effects of hunger and priming.

Conducted 2 experiments with a total of 8 male Charles River albino rats. In Exp I, using a runway paradigm, pretrial electric stimulation of the brain (ESB), food deprivation, and to a lesser extent water deprivation increased the running speed to an ESB reward. The trial-by-trial course of the change in running speed after the manipulation of food deprivation resembled the steplike performance effect seen when pretrial priming ESB was changed rather than the incremental learning effect seen when the response contingent ESB was changed. In Exp II, pretrial ESB inhibited running for food. Results suggest that hunger and pretrial ESB enhance rats' performance for an ESB reward, but act in opposing directions on their performance for a food reward. Implications for Deutsch's model of self-stimulation are discussed. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of relative magnitude of reward and type of need on satisfaction.

Tested the hypothesis of an interaction between type of need and magnitude of relative reward in their effect on level of satisfaction. It was predicted that there would be gradually increasing differences between satisfaction scores of large vs small magnitude of relative reward as the need was located in a higher position on A. Maslow's (1954) need hierarchy (excluding the self-actualization need). The analysis of the reactions of 40 female married 18-40 yr old undergraduates to a questionnaire designed for this purpose confirmed the hypothesis. Findings are discussed in terms of the social comparison and Maslow's hierarchy theories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Relative steepness of approach and avoidance gradients as a function of magnitude and valence of incentive.

20 undergraduates tapped rapidly to either win (approach) or avoid losing (avoidance) sums of money. The experimental design permitted height and steepness of arousal gradients to be examined as a function (a) of magnitude of incentive, with valence and quality of incentive held constant; and (b) of valence of incentive, with magnitude and quality of incentive held constant. An increase in incentive increased both the slope and height of approach and avoidance arousal gradients. Results support the conceptualization of motive strength as a multiplicative function of drive-related cues and an internal state rather than as an additive function, as proposed by N. E. Miller (1944, 1959). Avoidance gradients were significantly steeper than approach gradients, but the effect was not very robust and was far from uniform across Ss, some of whom produced much steeper approach than avoidance gradients. It is concluded that although there may be an intrinsic tendency for avoidance gradients to be steeper than approach gradients, this tendency is not strong and is easily reversed, giving rise to "avoidance–approach" conflict. Such conflict has interesting theoretical and practical implications that have not been recognized because of uncritical acceptance of the assumption that avoidance gradients are invariably steeper than approach gradients. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Extinction of conditioned fear in rats as a function of several parameters of CS exposure.

Employed Pavlovian fear acquisition and extinction procedures in a factorial design which varied conditioned-stimulus (CS) duration in acquisition, the number and duration of CS exposures in extinction, and total CS exposure across extinction trials. Ss were 128 female Blue Spruce hooded rats. Suppression of licking for water served as the measure of residual fear. The data revealed that suppression of licking was an inverse function of total nonreinforced CS exposure irrespective of the number and duration of extinction exposures used to amass that total. The effect of total nonreinforced CS exposure was not significantly influenced by the duration of the CS utilized in acquisition training. The discrepancy between the obtained results and predictions derived from several theories of extinction is discussed. (22 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)     

Resistance to extinction in rats as a function of deprivation level and schedule of reward in acquisition.

Conducted 3 straight-alley investigations with 84 male and 44 female Holtzman albino rats. 2 levels of deprivation were combined factorially with 2 schedules of reward (50 or 100%) in acquisition. Deprivation level in extinction was equated. When extinction deprivation level was low either there was no difference in extinction due to acquisition deprivation level or groups trained under high deprivation were more resistant to extinction than groups trained under low deprivation, as they were when deprivation level was high in extinction. It is suggested that at least 2 factors influence resistance to extinction as a function of acquisition deprivation level deprivation-related stimuli and some factor which produces greater resistance to extinction following high deprivation in acquisition. (17 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preference for delayed reward as a function of age, intelligence, and length of delay interval.

"Using a simple choice measure of preference for delayed reward on elementary school children… ranging in age from 5 to 12, and under five different lengths of delay interval, the following hypotheses were tested and confirmed: (a) preference for delayed reward is positively related to age; (b) positively to intelligence; (c) and negatively to length of the delay interval… . An additional finding was that subjects preferring the immediate reward tend to have more variable future time perspectives and that length of time perspective is slightly related to IQ, but not to age." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Feeding rate and responses to food deprivation as a function of fasting-induced hypoglycemia.

Examined the relation between hypoglycemia induced by 3 hrs of food removal at various times throughout the day and the amount eaten during the corresponding ad-lib periods in 48 male Wistar rats. Deprivation-induced hypoglycemia differed between the nighttime and the daytime and also between the beginning and the end of the daytime. A highly significant correlation existed between the 3-hr ad-lib intake and this time-dependent fall in blood glucose, which in turn was related to increases in subsequent intakes. It is concluded that rats eat at a rate just required to prevent hypoglycemia under ad-lib conditions and that after blood deprivation they transiently increase this rate to correct the fall in blood glucose and to reestablish the required supply of glucose to tissues. (11 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning in honeybees (Apis mellifera) as a function of sucrose concentration.

Foraging honeybees (Apis melliferan) were trained with 2 successively presented targets differing in color or odor, one of which always contained a 5-μl drop of 50% sucrose solution and the other, a 5-μl drop of 20% sucrose solution. Latency of response to each target was measured during the training, and at the conclusion, preference was measured in an unrewarded choice test. Analysis of the latencies showed both a prospective effect (faster response to the 50% target than to the 20% target) and a nonassociative retrospective effect (faster response after leaving the 20% target than after leaving the 50% target) reminiscent of the frustration effect in rats. The results both for retrospective latency and for choice can be understood on the simple theory that the attractiveness of a target depends on the strength of its association with sucrose and that the effect of concentration is on asymptotic strength. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

Anticholinesterase amnesia as a function of massed or spaced retest.

Hypothesized that if anticholinesterase-induced amnesia is the consequence of the accumulation of acetylcholine at the synapse, and if trials during retest are spaced, the level of acetylcholine should decrease and amnesia should disappear. 128 female Sprague-Dawley albino rats were retested under spaced and massed conditions. Under massed conditions the usual anticholinesterase-induced amnesia was observed. Under spaced conditions, retention was unaffected. Reversal training under anticholinesterase with massed and spaced conditions strengthened the conclusion that a memory deficit and not a performance deficit is caused by physostigmine. (PsycINFO Database Record (c) 2010 APA, all rights reserved)