Variable-interval Food Reinforcement Research Articles

ＶＩ強化によって維持しているラットのレバー押し反応に対するＶＲ罰の効果

The effects of reinforcement and punishment on response suppression under variable-interval reinforcement and variable-ratio punishment schedules were investigated. At baseline, lever pressing in rats was maintained by a variable-interval food reinforcement schedule. In the punishment condition, responding was punished by a grid shock under a variable-ratio schedule in which three rats experienced four or five punishment rates and a fixed reinforcement rate. Results indicated that there was a negative linear correlation between the variable-ratio punishment rate and the response rate. Results of three rats that experienced five or six reinforcement rates with a fixed punishment rate indicated that punishment suppressed responding at all reinforcement rates. These findings suggest that the punishment rate was strongly related to response suppression under both variable-interval reinforcement and variable-ratio punishment schedules.

Response reduction through the superimposition of continuous reinforcement: a systematic replication.

Prior clinical research suggests that superimposition and subsequent removal of a schedule of continuous reinforcement (CRF) may be a viable rate-decreasing procedure in that an extinction-like condition is arranged. The arrangement of similar conditions in the laboratory, however, resulted in the quick recovery of baseline rates. Lever-pressing patterns of eight male rats maintained by different schedules of variable-ratio and variable-interval food reinforcement were examined in an A-B-A experimental design of CRF food superimposition and removal. Responding was substantially reduced during the superimposition of CRF. Upon removal of the superimposed schedule, responding quickly approached presuperimposition baseline rates.

The influence of positive and negative reinforcement on selective attention in the rat

In Experiments 1 and 2 rats were trained under two multiple schedules of reinforcement. In one, bar pressing during a tone-light compound stimulus was reinforced under a variable-interval food reinforcement schedule. In the other multiple schedule, bar pressing avoided grid shock on a free-operant schedule. In both multiple schedules, a discrimination was maintained by an extinction schedule that was operative during the absence of the tone-light compound. In Experiments 1 and 2 the intensity of the tone-light compound was manipulated over three levels. Subsequent extinction tests revealed that light was attended to, almost exclusively of the tone, when food reinforcement had maintained bar pressing. On the other hand, the tone gained considerable attentional control under the shock avoidance schedule. This stimulus-reinforcer interaction was maintained for all three levels of the compound intensity. In Experiment 3 it was investigated whether this interaction was associative by presenting shock during the absence of the tone-light compound when food reinforcement maintained responding, and food during the absence of the compound when shock avoidance maintained responding. Since both food and shock were presented during a single session for both schedules, nonassociative effects of the reinforcing stimuli were equivalent across the schedules. Nevertheless, the stimulus-reinforcer interaction was maintained, indicating that the interaction was an associative effect.

GENERALIZATION PEAK SHIFT IN RATS UNDER CONDITIONS OF POSITIVE REINFORCEMENT AND AVOIDANCE

Rats were trained to discriminate between two click frequencies. One frequency was associated with either variable-interval food reinforcement (Experiment 1) or free-operant avoidance (Experiment 2). The other frequency was associated with the absence of food in Experiment 1 and the absence of shock in Experiment 2. On a click frequency generalization test, the rats in both experiments showed positive peak shift with the shape of the relative gradients being very similar. This is the first reported instance of peak shift in rats when responding was maintained by an avoidance contingency. Nondifferentially trained controls showed that this shift was due exclusively to associative processes, with nonassociative stimulus factors in themselves apparently making no contribution to increased rates at particular stimulus values. These results show the comparability of appetitive and aversive control and support the position that gradient differences do not result from approach versus avoidance per se.

Transfer of conditioned suppression and conditioned acceleration from instrumental to consummatory baselines

Following training on a variable-interval food reinforcement schedule, rats were exposed to Pavlovian procedures which produced reliable conditioned suppression and conditioned acceleration of the leverpressing (instrumental) baseline. When free food was simultaneously made available in the test cage, all subjects spent the majority of each session “freeloading,” that is, eating food from a dish rather than leverpressing for it. When superimposed upon the freeloading baseline, the conditioned suppression and conditioned acceleration procedures affected the rate of pellet consumption identically in magnitude and direction to their previous effects on leverpressing. These results suggest a motivational mechanism for conditioned suppression and acceleration, rather than one which depends upon spurious punishment of specific response sequences.

CHOICE PERFORMANCE IN SEVERAL CONCURRENT KEY‐PECK TREADLE‐PRESS REINFORCEMENT SCHEDULES1

Five pigeons were exposed to several concurrent variable-interval food reinforcement schedules. For three subjects, one component of the schedule required a key-pecking response, the other a treadle-pressing response. For the other two subjects, both schedule components required treadle-pressing responses. The relative probability of reinforcement associated with the manipulanda was varied from 0 to 1.0 in 13 experimental conditions for the Key-Treadle subjects and nine conditions for the Treadle-Treadle subjects. The results indicated that the logarithms of relative time spent responding, and the logarithms of relative number of responses emitted on a manipulandum, approximated direct linear functions of logarithms of the relative frequencies of reinforcement associated with that manipulandum. No systematic bias in favor of time spent key pecking over time spent treadle pressing was apparent for the Key-Treadle subjects. All subjects exhibited undermatching, in that the ratios of time and response allocation at the alternatives systematically differed from the ratios of reinforcers obtained from the alternatives in the direction of indifference. Key pecking appeared to have no special link to food beyond treadle pressing or what would be expected on the basis of the reinforcement dependencies alone.

Perinatal hypothyroidism in rats: persistent motivational and metabolic effects.

Five groups of female rats which were exposed to thiouracil for varying periods around the time of birth were compared with a 6th group of untreated controls in motivational, metabolic, and hormonal test situations during adolescence and adulthood. The thiouracil-treated rats displayed reduced fearfulness in lever-touching and lever-pressing tasks in operant conditioning chambers and in their initial adaptation to activity-wheel and maze apparatuses. These rats also showed hyperactivity in asymptotic running-wheel performance, increased spontaneous recovery of extinguished lever-pressing, and elevated responding in lever-pressing for variable-interval food reinforcement. A supplemental study revealed significantly greater ad libitum food and water intake and oxygen consumption in male thiouracil-treated rats and elevated serum thyroxine levels in thiouracil-treated females. In general the results indicate that perinatal thyroid deficiency engenders a chronic hypermetabolic state in both sexes which may be associated with a persistent, mild hyperthyroid condition in the case of female rats.

Polydipsia in adult mice and rats given corticosterone in infancy: accentuation by variable interval food reinforcement.

Mice and rats were given crystalline corticosterone subcutaneously at 2 days of age, and water intake was measured when the animals were adult. In both species, corticosterone-treated animals consistently drank more water than their littermate controls when at rest in their home cages. In rats, there was no difference in food consumption relative to body weight, and urine volume responded equally well to withdrawal of water. The polydipsia of steroid-treated rats was greatly accentuated when the animals were working for food on a variable-interval schedule (VI 60-sec.) with free access to water. The findings are compatible with other evidence suggesting lasting alterations in the emotional disposition of rodents after hypercorticism in infancy. When mice or rats are given intensive corticosterone treatment during infancy and then allowed to grow to maturity without further manipulation, they show evidence of lasting alterations in certain behavioral patterns, such as exploration of an open field (Howard & Granoff, 1968), performance on various food-reinforced operant schedules (Howard, 1973), and acquisition of 2-way conditioned active avoidance (Olton, Johnson, & Howard, in press). The present paper extends these observations to include drinking behavior and reports the existence of increased water intake in adult mice and rats given an implant of crystalline corticosterone at 2 days of age. Water intake was measured both when the animals were at rest in their home cages and during bar pressing for food with water freely available. The latter condition is of interest in view of the observations of Falk (1961, 1969), who found polydipsia in normal rats bar pressing for food on a variable interval schedule of 60 sec. (VI 60-sec.). The polydipsia induced by operant schedules has been considered to be psychogenic be

Effect of a signal previously paired with free food on operant response rate in pigeons

In Phase 1, food was presented independently of the birds’ behavior. In one group, the food was paired with an auditory CS; in the other group, CS and food occurred randomly. In Phase 2, the birds were trained to peck a key for variable-interval food reinforcement, with CS off. Then, following additional Phase 1 training, they were tested with CSs presented during operant extinction. For both key pecking and a photocell measure of activity near the speaker, the CS produced changes in behavior which, when measured independently of the direction of change, were significantly greater in the paired group than in the random group.

Differential responses to line orientation after training to a blank stimulus

Pigeons were trained to respond with variable-interval food reinforcement in the presence of a green key. During extinction, lines of different orientation were projected on the green field. Responding to these stimuli was differential but idiosyncratic. These findings may present methodological problems to Es using two dimensions to measure gradients of generalization of inhibition.

BEHAVIORAL CONTRAST IN CHAINED SCHEDULES1

In each of two experiments, the rate of key pecking maintained by a variable-interval food reinforcement schedule was measured, first when that schedule was studied in isolation, and then when it was correlated with the second component of a two-component chained schedule. In the first experiment, the first component of the chained schedule was correlated with a fixed-interval schedule; in the second experiment it was correlated with a variable-interval schedule. In both experiments, behavioral contrast was demonstrated in the second component of the chained schedule. Compared to the rate of responding on the food-reinforcement schedule when it had operated in isolation, the rate of responding on the food-reinforcement schedule when it was correlated with the second component was higher, while the rate on the schedule of the first component was lower. The results are discussed with reference to the determinants of contrast.

ENHANCEMENT OF OFF‐KEY PECKING BY ON‐KEY PUNISHMENT1

Under a variable-interval food reinforcement schedule, some of a pigeon's pecking responses land on the wall area adjacent to the response key. These off-key pecks increase in frequency when key responses produce shocks and decrease when shock is removed.

Response patterning during stimulus generalization in the rat.

Nine rats were trained to bar press in the presence of a clicking sound of 6.67 cps (S(D)) for 1-min variable-interval food reinforcement randomly alternated with a clicking sound of 20 cps (S(Delta)) signifying extinction. After a criterion of 90% of total responses in the presence of the S(D) was obtained, a generalization test was administered, including values of 6.67, 10.00, 13.33, and 20.00 cps, with responses in the presence of the S(D) continuing to be reinforced during testing. The test yielded a gradient of response strength with rate highest in the presence of the S(D) and decreasing with increasing distance from this value. An interresponse time (IRT) analysis of responding during generalization testing revealed no systematic differences in modal IRT category or in median IRT to the different test stimuli. Mean IRT was lowest in the presence of the S(D) and increased systematically with increasing distance from this value, supporting the hypothesis that the generalization gradient of response rate is primarily the result of an increasing proportion of "long" IRT responses to stimuli increasingly distant from the S(D).

Variable-interval punishment during variable-interval reinforcement.

Variable-interval punishment was superimposed on a variable-interval food reinforcement baseline for three groups of rats. The value for the variable-interval punishment schedule was the same as that for the variable-interval food reinforcement schedule, although the two schedules were programmed independently. The three groups were Variable Intervals 0.5, 1, and 3 min. Little or no suppression occurred in the three groups at mild (0.2 and 0.4 ma) intensities of punishment, but at 0.6 ma, complete suppression occurred almost uniformly. During continued punishment, there was no consistent recovery toward the pre-punishment baseline at suppressing intensities of punishment. After punishment was discontinued, recovery from suppression was more rapid the lower the punishment intensity, and the lower the value of the variable-interval schedules of reinforcement and punishment.

Licking behavior of rats on a schedule of food reinforcement.

Rats were trained on a variable-interval food reinforcement schedule. Lever presses and licks at the milk reinforcement were recorded independently. A dose of d-amphetamine which increased lever-pressing rates failed to affect licking rates. Licking rates increased as the duration between reinforcements on the variable-interval schedule increased.

Some observations on the adventitious reinforcement of drinking under food reinforcement.

The development of strong postreinforcement drinking behavior under variable-interval food reinforcement in rats was found to be influenced by the proportion of short intervals in the VI and the proximity of the water tube to the lever.