Effects of post-session wheel running on within-session changes in operant responding

This study tested the effects of post-session wheel running on within-session changes in operant responding. Lever-pressing by six rats was reinforced by a food pellet under a continuous reinforcement (CRF) schedule in 30-min sessions. Two different flavored food pellets were used as reinforcers. In the wheel conditions, 30-min operant-sessions with one of the flavored pellets were followed by 30-min free-wheel running sessions. Meanwhile, in the home conditions, rats’ operant responding was reinforced by the other flavored pellets during 30-min operant-sessions, and the rats were then returned to their homecages. All rats were exposed to 4 wheel and 4 homecage sessions. Operant responding was lowered during the wheel conditions. However, post-session running did not alter the within-session pattern of operant responding. These effects were practically identical to the effects of drug-induced taste-aversion learning on within-session changes in operant responding, suggesting similar mechanisms in both taste-aversion preparations.     

Behavioral economics and within-session changes in responding

Pigeons and rats responded on fixed-ratio schedules with requirements ranging from 5 to 120 responses. Consistent with past results from several schedules and procedures, responding usually changed systematically within experimental sessions. The within-session changes were usually larger and were less symmetrical around the middle of the session for schedules that provided higher, rather than lower, rates of reinforcement. These results suggest that similar variables contribute to within-session changes in responding under different schedules. When an economic demand function was fit to the data, the intensity and elasticity of demand for food and the percentage of the variance accounted for decreased within sessions, although the trend for elasticity did not reach statistical significance for pigeons. These results suggest that relatively short sessions should be used to study economic demand in open economies and that demand may differ at different times in a session and in sessions of different lengths. Within-session changes in intensity, but not necessarily elasticity, of demand are consistent with behavioral economic theories.     

Prospective factors contribute little to within-session changes in responding

Five rats pressed levers for food delivered by a multiple variable interval 1-min variable interval 1-min schedule. In theunpredictable conditions, sessions were 20, 40, 60, 80, or 100 min long, determined randomly at the beginning of each session. In thepredictable conditions, each of these session durations was presented for 15 consecutive sessions. Rate of responding changed systematically within the session even when the end of the session was unpredictable. This implies that prospective factors related to anticipation of the end of the session are not necessary for producing withinsession changes in responding. Within-session patterns of responding were also similar for the predictable and unpredictable conditions. This suggests that prospective factors contributed little to the form of the within-session patterns under the present conditions.     

Criticisms of the satiety hypothesis as an explanation for within-session decreases in responding

The authors of four papers recently reported that satiation provides a better explanation than habituation for within-session decreases in conditioned responding. Several arguments question this conclusion. First, the contribution of habituation to within-session changes in responding seems clearly established. Information that is consistent with habituation, but that is difficult to reconcile with satiation, is not adequately addressed. Second, the limited evidence offered in support of satiation is ambiguous because the results are just as compatible with habituation as with other satiety variables. Finally, the term satiation is used in an intuitive way that is sometimes contradicted by research about the termination of ingestion. Use of the technical term satiation in a way that differs from its conventional usage will only isolate operant psychology from other areas of psychological research.     

Effect of auditory isolation on activity-based anorexia

The objective was to study male and female rats exposed to Activity-Based Anorexia (ABA; simultaneous exposition to food restriction and free access to an activity wheel) under two conditions of sound attenuation, by means of different arrangements of wheels (standard versus isolation) in the laboratory room. Regardless of the sound attenuation condition, all but one male and one female with access to wheels had to be removed from the experiment, but extended ABA endurance was found in rats in the sound attenuation condition. Furthermore, significantly lower levels of running were observed in both males and females under the sound attenuation arrangement in the isolation condition. The results suggest that external stimulation plays a role in the activity displayed by rats exposed to ABA, and that the reduction of external stimulation diminishes running but does not protect rats from developing ABA.     

Towards a mathematical model of within-session operant responding

Operant response rate changes within the course of a typical free-operant experimental session. These changes are orderly, and reliably demonstrated with subjects from different species, responding under different experimental conditions. Killeen (1995) postulated that the response rate changes are a function of the interplay between arousal and satiation and offered a mathematical model for this hypothesis. Here we analyze Killeen's model, demonstrating that, although solid in its principles, it presents some flaws in its implementation. Then, based on the same principles, we build and test a new model of within-session motivation dynamics. We also demonstrate that, by representing arousal as a variable that ranges between 0 and 1, we can obtain a surprisingly simple model of free-operant response rate.     

A procedure for studying the within-session onset of human drug discrimination.

The purpose of the present study was to develop a procedure for measuring the within-session onset of human drug discrimination. During daily sessions, under double-blind conditions, caffeine-abstinent adults ingested a letter-coded capsule containing 178 mg caffeine or placebo. Trials were presented at 30-s intervals, beginning immediately after drug ingestion and continuing for 60 min. On each trial, subjects could guess which of their two letter-coded drugs they had received by pressing a left button (for one drug) or right button (for the other drug); subjects could also press a center "no guess" button instead of guessing. Each trial ended after one button press. After each session, subjects were told which drug they had received. Subjects earned one point (worth $0.10 per point) for each correct guess. Subjects lost either 0, 1, or 10 points for each incorrect guess; the point-loss contingencies were varied in random order across sessions. Discrimination earnings accumulated across all sessions. The point-loss contingencies decreased random responding and delayed the discrimination time course. Overall, this procedure provided an orderly and relatively continuous measure of the within-session onset of drug discrimination and should have a range of applications in understanding the human behavioral pharmacology of drugs.     

Preadaptation to the feeding schedule does not eliminate activity-based anorexia in rats

To test whether activity-based anorexia (ABA) still occurs after preadaptation to the feeding schedule, 20 rats were first exposed to a feeding schedule of one 90-min meal per day until adaptation occurred (measured by maintenance of stable body weight). Then, during ABA training, half the rats (wheel group) were confined in running wheels except during the daily meal, and half (cage group) were not. Wheel running suppressed feeding—that is, food intake in the wheel group was less than that in the cage group. Also, the rats in the wheel group lost weight, whereas those in the cage group did not. Wheel running increased over days. Thus, the defining characteristics of ABA were evident in rats that were not subjected to ABA training until after they had become well adapted to the feeding schedule. These findings support the view that the suppression of feeding produced by wheel running triggers the vicious circle of ABA. They also cast doubt on the hypothesis that activity-induced interference with adaptation to the feeding schedule plays a key role in causing ABA.     

Habituation contributes to within-session changes in free wheel running.

Three experiments tested the hypothesis that habituation contributes to the regulation of wheel running. Rats ran in a wheel for 30-min sessions. Experiment 1 demonstrated spontaneous recovery. Rats ran more and the within-session decreases in running were smaller after 2 days of wheel deprivation than after 1 day. Experiment 2 demonstrated dishabituation. Running rate increased immediately after the termination of a brief extra event (application of the brake or flashing of the houselight). Experiment 3 demonstrated stimulus specificity. Rats completed the second half of the session in either the same wheel as the first half, or a different wheel. Second-half running was faster in the latter case. Within-session patterns of running were well described by equations that describe data from the habituation, motivation, and operant literatures. These results suggest that habituation contributes to the regulation of running. In fact, habituation provides a better explanation for the termination of wheel running than fatigue, the variable to which this termination is usually attributed. Overall, the present findings are consistent with the proposition that habituation and sensitization contribute to the regulation of several forms of motivated behavior.     

Effects of signals preceding and following shock on baseline responding during a conditioned-suppression procedure

Long-Evans rats were exposed to a succession of conditioned-suppression procedures involving pairings of (1) signal-shock, (2) shock-signal, and (3) a signal-shock-signal sequence in which first and second signals were at first physically identical. Traditional suppression of food-reinforced responding was obtained under the signal-shock arrangement, and exposure to the shock-signal sequence resulted in conditioned enhancement of responding during the signal. The signal-shock-signal condition reliably suppressed responding during the first signal, but produced no differential effect on response rate during the second signal. Baseline responding was least changed from preshock rates under the signal-shock-signal procedure, but baseline rate was considerably reduced under the signal-shock and shock-signal arrangements, the latter yielding most substantial reductions. A second experiment indicated that the magnitude and direction of changes in baseline responding reported in Experiment I were not confined to cases in which the first and second signals in the signal-shock-signal arrangement were physically identical. It is suggested that the major effects of the conditioned-suppression procedure on response rate might not be confined to presentations of the signal.     

Absence of effect of the change of food context in the activity-based anorexia phenomenon in rats

The goal of this study was to analyse how the context in which animals remain during the period of access to food modulates the development of activity-based anorexia in rats. For this purpose, the effect of changing the context of the activity period and the eating period was measured in terms of body weight loss, reduction in food intake and increase in physical activity. A 2 yen 2 factorial design was implemented, by having or not having access to a running wheel, and by being exposed or not exposed to a context change. Results showed that exposure to different contexts for the wheel and for the food did not affect weight loss, food intake or activity levels. These results are in line with the theoretical position of Epling and Pierce (1992) that activity is induced by the food restriction regime.     

Effects of timeout on spaced responding in pigeons

Three pigeons were trained under a differential-reinforcement-of-low-rate schedule of 20 sec, and then exposed to a schedule under which responses terminating interresponse times less than 20 sec produced timeout and responses terminating interresponse times greater than 20 sec produced reinforcement. Response-produced timeouts selectively decreased the probability of short interresponse times and thereby produced a higher frequency of reinforcement. The suppressive effect of timeout was independent of timeout duration, with timeouts of 5, 10, or 20 sec. Similar effects were found when the minimum interresponse time that could be terminated by response-produced reinforcement was increased to 30 sec. The suppressive effects of timeout on responding maintained by these schedules were similar to previous reports in which responding was punished with electric shock.     

Within-session changes in responding during several simple schedules

Pigeons' key pecking was reinforced by food delivered by several fixed-interval, variable-ratio, and differential-reinforcement-of-low-rate schedules. Rate of responding, number of responses per reinforcer, length of postreinforcement pause, running response rate, and the time required to collect an available reinforcer changed systematically within sessions when the schedules provided high rates of reinforcement, but usually not when they provided low rates. These results suggest that the factors that produce within-session changes in responding are generally similar for different schedules of reinforcement. However, a separate factor may also contribute during variable-ratio schedules. The results question explanations for within-session changes that are related solely to the passage of time, to responding, and to one interpretation of attention. They support the idea that one or more factors related to reinforcement play a role.     

Effects of a concurrent task on fixed-interval responding in humans

Subjects pressed a telegraph key to illuminate a meter dial on which pointer deflections appeared at fixed intervals. Upon detecting a deflection they were required to press another key to reset the pointer to zero. This detecting and resetting operation reinforced the behavior of pressing the light-flashing key (i.e., the observing responses). The usual pattern of responding on the light-flashing key was a long pause following the reinforcement and an abrupt transition to a steady response rate toward the end of the interval. When the subjects were required to perform a concurrent subtraction task, the pattern of responding changed in varying degrees, ranging from complete loss of typical fixed-interval behavior to a slight shortening of the post-reinforcement pause. These effects were attributed to the disruption of the self-produced verbal chains (counting or reciting) that ordinarily govern human behavior on this schedule.     

Effects of d-amphetamine and chlordiazepoxide on spaced responding in pigeons

The effects of d-amphetamine and chlordiazepoxide were studied in pigeons on performance (1) under a schedule that reinforced responses on a key (food key) if they were more than 20 sec apart, (2) under the same schedule when responses also were required on a collateral key during the interresponse time on the food key, and (3) under the same schedule when responses were required on a collateral key during the interresponse time on the food key and collateral-key responses could produce a stimulus correlated with the availability of food. Under all three spaced-responding schedules, d-amphetamine and chlordiazepoxide at low dose levels slightly increased the frequency of short interresponse times on the food key for about half the birds, and either did not affect the interresponse time patterns of the other birds, or lengthened the durations slightly. At higher dose levels, d-amphetamine and chlordiazepoxide increased the frequency of long interresponse times or abolished responding in all birds. Changes in the pattern of interresponse times on the food key did not seem to depend on changes in the rate or pattern of collateral-key responses.     

Studies on responding under fixed-interval schedules of reinforcement: the effects on the pattern of responding of changes in requirements at reinforcement

In pigeons responding under a 180-sec fixed-interval schedule of reinforcement, the frequency distribution of the duration of the final interresponse time before the reinforcer was compared with the distribution of the preceding two interresponse times. The results confirmed qualitatively and quantitatively the expected preferential reinforcement of longer interreinforcement times under fixed-interval reinforcement. Requirements at reinforcement were then changed to eliminate the preferential reinforcement of longer interresponse times. Local patterns and mean rate of responding could change, without the characteristic fixed-interval pattern of increasing responding through the interval (scalloping) being much affected. It is concluded that this characteristic pattern of fixed-interval responding does not depend crucially on effects of the reinforcer at the moment of reinforcement, but rather to effects extending over much longer periods of time than just the last interresponse time.     

Rats’ memory for time and relational responding in the duration-comparison procedure

Rats were trained in a duration-comparison task to press one lever if the comparison duration (c) was 1.2-s shorter than a standard duration (s), and another lever if c was 1.2-s longer than s. The interval between s and c duration was 1 s. The 10 duration pairs used during training controlled for the absolute duration of c and the total duration of an s-c pair. The total duration of an s-c pair was not predictive of the correct response. In Experiment 1, during equal-duration pair test trials, rats increasingly responded long (i.e., c > s) as the s-c delay was lengthened. In Experiment 2, long responding increased as the s-c delay was lengthened, even when the illumination condition during the s-c delay differed from that during the intertrial interval (ITI). In Experiment 3, transfer to novel duration pairs was assessed. Overall accuracy for the novel duration pairs was significantly above chance, but transfer performance was also affected by the absolute value of the novel c durations. This is the first study to demonstrate that rats can acquire relational duration discriminations. As in previous studies with pigeons the evidence was consistent with subjective-shortening of the standard duration and there was also evidence of a reliance on a mixture of absolute and relational strategies in responding.     

Three-month-old infants' object recognition across changes in viewpoint using an operant learning procedure

Object knowledge refers to the understanding that all objects share certain properties. Various components of object knowledge (e.g., object occlusion, object causality) have been examined in human infants to determine its developmental origins. Viewpoint invariance--the understanding that an object viewed from different viewpoints is still the same object--is one area of object knowledge, however, that has received less attention. To this end, infants' capacity for viewpoint-invariant perception of multi-part objects was investigated. Three-month-old infants were tested for generalization to an object displayed on a mobile that differed only in orientation (i.e., viewpoint) from a training object. Infants were given experience with a wide range of object views (Experiment 1) or a more restricted range during training (Experiment 2). The results showed that infants generalized between a horizontal and vertical viewpoint (Experiment 1) that they could clearly discriminate between in other contexts (i.e., with restricted view experience, Experiment 2). Overall, the outcome shows that training experience with multiple viewpoints plays an important role in infants' ability to develop a general percept of an object's 3D structure and promotes viewpoint-invariant perception of multi-part objects; in contrast, restricting training experience impedes viewpoint-invariant recognition of multi-part objects.