Alteration of classically conditioned heart rate by operant reinforcement in monkeys.

Ran 6 adolescent male rhesus monkeys alternately on classical conditioning and on operant heart rate training schedules. The classical unconditioned stimulus (UCS) was identical to the operant negative reinforcement. After operant training, some Ss changed their heart rate responses to the classical conditioned stimulus (CS). When both the operant and the classical schedules were in force simultaneously, all Ss changed their previous heart rate responses to the classical CS without significantly changing their blood pressure responses to this stimulus. The changes in heart rate response to the CS sometimes persisted long after the operant schedules were no longer in force. These results show that a classically conditioned response can be altered by operant reinforcement, and they suggest that the classical UCS actually may be an operant reinforcer. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long-term self-intravenous "drinking" in the rat.

Results of a series of experiments show that male Wistar albino rats, when water was available only by intravenous self-injection, learned to rehydrate by pressing a lever even after desalivation and for periods up to 90 days. It appears that hydromineral regulation was occurring about a new, lower set point for body fluid content which was necessary for the onset and maintenance of intravenous "drinking." The regulatory nature of the operant was confirmed by appropriate modulation of operant rate to amount of reinforcement per leverpress and in tonicity of self-injected fluid. There seemed to be some "motivational deficits," and these Ss did not respond for intravenous water as the oral controls did when challenged with traditional intra- and extracellular thirst stimuli. More complex stimuli (e.g., heat and salty food) led to compensatory responding. While interoceptors alone seemed capable of eliciting the defense of a homeostatic hydromineral balance, the control over the operant was less precise than for normal oral drinking. (57 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Choice between fixed and variable delays to reinforcement in the adjusting-delay procedure and concurrent chains.

A generalization of the contextual choice model ([CCM]; R. C. Grace, see record 1994-28397-001) is presented that describes preference between fixed and variable schedules in concurrent chains and the adjusting-delay procedure. In Exp 1A and 1B, fixed-delay indifference values for pigeons for a series of variable-delay schedules were obtained, using the adjusting-delay procedure, to test a Weber's law invariance and the effectiveness of several models. These data were then used to generate, in Exp 2, pairs of fixed and variable schedules that should have been equally preferred in concurrent chains. As predicted, deviation from indifference was small. These results indicate that (a) the determiners of value in the 2 procedures are the same, (b) the delay of reinforcement gradient is best represented as a power function with a delay threshold, and (c) a single model (CCM) can accurately describe data in the 3 most popular operant choice paradigms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neurochemical regulation of feeding in the rat: Facilitation by a-noradrenergic, but not dopaminergic, receptor stimulants.

42 male Charles River rats ate voraciously after intraventricular injections of the a-noradrenergic receptor stimulant clonidine. Intraventricular administration of levonorepinephrine also facilitated feeding, but similar injections of dopamine and apomorphine (a dopamine receptor stimulant) were ineffective and even tended to suppress feeding. Clonidine was 100 times more potent than norepinephrine and increased the intake of both the ordinary diet of powdered food and a highly palatable wet food. The anorexic action of amphetamine was reversed by centrally administered clonidine. These observations suggest "respondent" rather tban "operant" regulation of feeding by noradrenergic systems. That is, in relation to noradrenergic mechanisms, feeding appeared to be a respondent which was sensitized or disinhibited by activation of a-noradrenergic receptors, rather than an operant which was reinforced by the release of norepinephrine. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning the temporal dynamics of behavior.

This study presents a dynamic model of how animals learn to regulate their behavior under time-based reinforcement schedules. The model assumes a serial activation of behavioral states during the interreinforcement interval, an associative process linking the states with the operant response, and a rule mapping the activation of the states and their associative strength onto response rate or probability. The model fits data sets from fixed-interval schedules, the peak procedure, mixed fixed-interval schedules, and the bisection of temporal intervals. The major difficulties of the model came from experiments that suggest that under some conditions animals may time 2 intervals independently and simultaneously. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

A "freeloading" effect: Changes in response rate following non-contingent food reward.

Trained 82 male albino rats to barpress on an operant schedule. Ss were then given noncontingent reward training with the bar removed, and retested on the barpressing response. In each of the 4 experiments, rates of responding were generally depressed following noncontingent rewards on either VI or FI schedules. Reward schedules during barpressing affected the depression effect very little. Several hypotheses were tested in the last 2 studies, but none were supported by the data. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral contrast in pigeons depends upon the operant.

Reinforced 3 male Carneaux pigeons for depressing a foot treadle according to multiple VI/VI schedules. After rates of responding stabilized, the schedule in 1 component was changed to extinction. This manipulation resulted in either no change or a decrease in rate of responding in the unchanged component. The Ss were then reinforced for key pecking under the same procedure. When key pecking was the operant, the experimental manipulation resulted in behavioral contrast. Results are discussed in terms of Pavlovian * Instrumental interactions. (17 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex differences in the relationship between activity and weight loss in the rat.

Access to a running wheel combined with restricted feeding produced body weight loss at an equivalent rate in male and female litter-mate rats (Experiment 1). Thus, despite weighing less and running more, females were not more vulnerable to this procedure. When factors influencing weight loss were varied, no sex difference was found in adaptation to a new feeding schedule or in the effect of single versus group housing (Experiment 2). The apparent critical difference was that body weight loss increased running in males but not in females (Experiment 3). In all rats, rapid recovery of body weight occurred when food access was no longer restricted (Experiment 1), suggesting that "activity-based anorexia" is a misnomer for weight loss by rats in a running wheel. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interresponse-time reinforcement and behavior under aperiodic reinforcement schedules: A case study using computer modeling.

Computer modeling was used to investigate the extent to which response rates under variable-interval and variable-ratio schedules are compatible with a simple process of interresponse time (IRT) reinforcement, as argued by Peele, Casey, and Silberberg (1984). Their computer model was duplicated, as well as its principal result of a large response rate difference between the interval and ratio schedules. After their model was run under a variety of interval and ratio schedules, it was found that the response rates produced did not exhibit patterns of sensitivity to schedule parameter variation found experimentally. Furthermore, the model predicted a large response rate difference between a variable-ratio and a "linear feedback" variable-interval schedule, contrary to the results of McDowell and Wixted (1986). We concluded that simple IRT reinforcement was probably not adequate as an explanation of schedule effects under aperiodic interval and ratio schedules, although a modification of the Peele et al. model incorporating behaviors that were not measured operants could exhibit schedule sensitivity. This suggested that realistic molecular models of schedule phenomena must involve more than simple IRT reinforcement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral contrast and behavioral momentum.

In Exp 1, 5 pigeons were trained to peck a key on multiple schedules of food reinforcement. The reinforcer rate was constant in 1 component and varied between conditions in the alternated component. In the constant component, steady-state response rate and its resistance to both prefeeding and extinction were inversely related to the reinforcer rate in the alternated component. Thus, resistance to both prefeeding and to extinction, like response rate, exhibits behavioral contrast. In Exp 2, a time-out period between schedule components eliminated contrast effects on steady-state response rate but not on resistance to extinction. The resistance-to-change results contradict expectations derived from current quantitative accounts of steady-state operant behavior and suggest instead that resistance to change depends on the contingency between component stimuli and reinforcers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

How pigeons estimate rates of prey encounter.

Pigeons were trained on operant schedules simulating successive encounters with prey items. When items were encountered on VI schedules, birds were more likely to accept a poor item (long delay to food) the longer they had just searched, as if they were averaging prey density over a short memory window (Exp 1). Responding as if the immediate future would be like the immediate past was reversed when a short search predicted a long search next time (Exp 2). Experience with different degrees of environmental predictability appeared to change the length of the memory window (Exp 3). The results may reflect linear waiting (J. J. Higa et al, 1991), but they differ in some respects. The findings have implications for possible mechanisms of adjusting behavior to current reinforcement conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Apprentissage vicariant dans une situation de conditionnement operant libre.

Investigated the quantitative and qualitative effects of fixed-ratio (FR) and fixed-interval (FI) reinforcement schedules on a free operant behavior acquired in a vicarious learning situation. 84 medical students underwent the direct or vicarious conditioning session. Complete vicarious acquisition was obtained with the FR schedule. With the FI schedule, response rates were lower than those recorded in the nonvicarious situation, but the temporal distribution of responses was inadequate and the behavioral pause was too brief following presentation of reinforcing stimuli. Observation of the entire conditioning session including the extinction phase did not lead to a more rapid extinction. It is suggested that the processes involved in the learning of the FR-controlled operant activity might be less complex and more immediately available to Ss, while in the FI condition the low perceptual saliency of relevant temporal factors might hinder the vicarious acquisition of the operant behavior. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of paleocerebellar lesions on DRL performance in the albino rat.

18 male albino rats with paleocerebellar lesions and 8 controls were trained to barpress for food on continuous reinforcement (CRF) and differential reinforcement of low response rates (DRL) schedules. Ss with lesions showed normal acquisition of the CRF schedule, but they exhibited a marked deficit on the DRL task. This deficit was related to overresponding that appeared to result from an inability to inhibit the response, rather than from a dysfunction in timing ability or motor capacity. The DRL deficit, however, was overcome by the introduction of a salient stimulus object (wood block) into the operant situation. Although no explicit reinforcement contingencies were placed on interaction with the stimulus object, it appeared that the wood block facilitated the development of "collateral" behaviors that served to mediate the DRL interval. Results are consistent with the suggestion that the cerebellum may contribute to the sequential organization of complex behaviors. (51 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of abstinence on cigarette smoking among outpatients with schizophrenia.

The authors of this study examined the effects of brief smoking abstinence on smoking among 6 individuals with schizophrenia or schizoaffective disorder. Before 6 of 12 experimental sessions, participants were required to provide breath carbon monoxide (CO) samples indicative of smoking abstinence; before the remaining sessions, participants provided CO samples indicating no abstinence. During sessions, participants obtained smoking opportunities (2 puffs/opportunity) under either fixed ratio-1 or progressive ratio (PR) schedules of reinforcement. Abstinence increased smoking under both schedules and increased breakpoint for smoking under the PR schedule. These data offer further evidence that smoking by individuals with schizophrenia is orderly, operant behavior that is modulated, at least in part, by variables that also affect smoking in people without major mental illness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Amphetamine and operant behavior in rats: Relationship between drug effect and control response rate.

Examined the effect of amphetamine on the rate of operant responding, using rats trained to press a lever for water reinforcement; 2 experiments were conducted with male albinos of the ZM/Sprague-Dawley strain. Amphetamine's effect was strongly correlated with the mean predrug rate of responding: drug-induced increases in rate were inversely proportional to control rates, while drug-induced decreases were directly proportional to control rates. This relationship was observed in different groups of Ss trained to perform on different types of reinforcement schedules (FR, FI, and VI), in a single group of Ss performing on different schedules of the same type (different FRs), and for a single group of Ss performing in different segments of the same schedule (FI). (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Food motivation and body weight levels in hypothalamic hyperphagic rats: A dual lipostat model of hunger and appetite.

Compared the food and water motivations of 26 normal and 29 hyperphagic female Carworth CFE rats using barpressing performance on continuous reinforcement, VI, and fixed-ratio schedules. Under conditions of food or water deprivation, hyperphagic Ss displayed normal barpressing rates for food or water when their body weights were limited to preoperative or control levels but subnormal barpressing rates when they were tested at obese body-weight levels. Under nondeprived conditions, dynamic hyperphagic Ss barpressed more than controls for a palatable milk diet, while obese hyperphagic Ss worked at control levels for this diet. The findings suggest a dual lipostat model of hunger and appetite to explain feeding and body weight regulations in normal and hypothalamic hyperphagic animals. (62 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Resistance to Extinction in the Steady State and in Transition.

Three experiments with pigeons explored the constancy of reinforcer omission during extinction conjectured by rate estimation theory. Experiment 1 arranged 3-component multiple variable-interval (VI) schedules with a mixture of food and extinction trials within each session. Reinforcers omitted to an extinction criterion increased with food-trial reinforcer rate. Experiment 2 arranged 3-component multiple VI schedules where components differed in rate or number of reinforcers. Resistance to extinction depended on the training reinforcer rate but not on the number of reinforcers omitted. Experiment 3 replicated the partial-reinforcement extinction effect within subjects in a discrete-trial procedure and found that more reinforcers were omitted in continuous- than in partial-reinforcement trials. A model of extinction based on behavioral momentum theory accounted for all the data. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex differences in physical dependence on orally self-administered phencyclidine (PCP) in rhesus monkeys (Macaca mulatta).

Withdrawal from orally self-administered phencyclidine (PCP) has been shown to alter operant baselines of food-maintained responding. The goal of the present study was to determine whether there are sex differences in these alterations. Seven female and 7 male rhesus monkeys (Macaca mulatta) were given concurrent access to PCP and water under fixed ratio (FR) 8 schedules during 2 daily sessions that alternated with 2 sessions during which pellet deliveries were contingent on lever presses under an FR 64 schedule. After operant responding stabilized, PCP was replaced by water for 10 days, and food access remained under the same schedule. Subsequently, concurrent PCP and water access was reintroduced for 10 days. This procedure was repeated with 3 PCP concentrations (0.125, 0.25, and 0.50 mg/ml) and 3 FR requirements for food-reinforced responding (64, 128, and 256). Disruptions in operant responding for food served as a quantitative measure of withdrawal severity. During PCP withdrawal, males showed a greater suppression of food-maintained behavior than females at the 2 highest PCP concentrations and the lowest FR requirement tested. Males responded more than females for PCP; however, when weight was taken into consideration, PCP intake (milligrams per kilogram) in males and females was equal. The data suggest that males may experience more severe withdrawal effects than females, and the duration of the adverse effects of withdrawal lasts longer in males than in females. This study is the 1st to use nonhuman primates to document sex differences in withdrawal severity as measured by a quantifiable baseline. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Timing in Choice Experiments.

In Experiment 1, pigeons chose between variable- and fixed-interval schedules. The timer for 1 schedule was reset by a reinforcement on that schedule or on either schedule. In both cases, the pigeons timed reinforcement on each schedule from trial onset. The data further suggest that their behavior reflects 2 independent processes: 1 deciding when a response should be emitted and responsible for the timing of the overall activity, and the other determining what this response should be and responsible for the allocation of behavior between the 2 response keys. Results from Experiment 2, which studied choice between 2 fixed-interval schedules, support those 2 conclusions. These results have implications for the study of operant choice in general. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Animals foraging in the lab: Problems and promises.

Foraging has become a popular catchword in literature like that published in this Journal. Several different kinds of psychological research on foraging can be distinguished. These include tests of optimal foraging models using operant schedules and other simulations, analyses of the mechanisms assumed as constraints in optimality models, tests of the optimality of behavior on arbitrary schedules, and use of seminaturalistic laboratory situations. This kind of work is not without problems. One is that the gap between "real" and simulated foraging has been insufficiently explored. More important, accounts of behavior in terms of function (e.g., optimal foraging theory) are often confused with those in terms of mechanisms of learning, memory, and choice. The most productive research strategy in this area is to juxtapose predictions of functional and mechanistic models and attempt to understand any differences between them. Studies of foraging behavior can also reveal new or poorly studied phenomena. Because optimal foraging theory makes ideas about function explicit and precise, well-formulated investigations of foraging behavior can contribute substantially to understanding learning, memory, and decision processes as biological adaptations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)