Response rate under varying frequency of non-contingent reinforcement

Two White Carneaux hen pigeons were exposed to a 60-sec random-interval baseline procedure. Six different exteroceptive stimuli were successively correlated, within a single session, with blocks of 10 reinforcement presentations. Following this training, a non-contingent reinforcement procedure was instated with inter-reinforcement intervals of 5, 15, 30, 60, 120, and 240 sec. Within a single session, each non-contingent frequency was correlated with one of the previously presented discriminative stimuli. After an initial increase in the rate of responding as the result of a high density of non-contingent reinforcements, the rate declined as exposure to each non-contingent frequency was prolonged.     

Some notes on conditioned suppression and reinforcement schedules

Two pigeons were trained on an FR 150 schedule of reinforcement. An Estes-Skinner conditioned suppression procedure was then superimposed on this performance at varied intervals. If the CS occurred during the early stages of the ratio run, complete suppression resulted. If the CS occurred during the later stages of the run, the birds continued to respond until the reinforcement was obtained, which was then followed by complete suppression.     

Effects of food deprivation and reinforcement magnitude on conditioned suppression

In Experiment I, the responding of rats lever pressing on a variable-interval schedule for sucrose solution was partially suppressed by a variable duration conditioned stimulus followed by shock. When food deprivation was increased, response rates during and before the conditioned stimulus increased monotonically. Varying the concentration of sucrose across blocks of sessions or from session to session in a semi-random sequence had little effect on response rates either before or during the conditioned stimulus. With a fixed sequence of increasing concentrations across a five-session block, increased concentration produced much more rapid increases in response rates before than during the conditioned stimulus. In Experiment II, rats were presented with the same sequence of increasing concentrations across a five-session block. When tested at 80% body weight, response rates increased rapidly as concentration increased, but at 100%, body-weight rates increased only slightly. The effect of a change in body weight in Experiment II thus mimicked the effect of the conditioned stimulus in the latter part of Experiment I. These findings support the view that the effect of a pre-aversive conditioned stimulus is similar to that of a change in food deprivation, but unlike that of a change in reinforcement magnitude.     

Frequency of reinforcement as a parameter of conditioned suppression

Two pigeons were trained on a multiple VI-1; VI-4 min schedule for food reinforcement until a stable differential rate of response was established. Each component of the multiple schedule was in effect for 10 min and was separated from the other by 1 min time out. An Estes-Skinner conditioned suppression procedure was superimposed on each component of the schedule. The relative magnitude of the suppression behavior was measured during its acquisition and extinction, and at CS durations of 100, 200, and 300 sec. The initial magnitude of the suppression behavior was less severe on the VI-1 baseline than on the VI-4, and it extinguished more rapidly on the VI-1. As the relative duration of the CS was increased, the suppression behavior became less severe on both baselines, but the initial differential magnitude in the suppression remained intact.     

Response rate and reinforcement rate in Pavlovian conditioning

Four experiments used delay conditioning of magazine approach in rats to investigate the relationship between the rate of responding, R, to a conditioned stimulus (CS) and the rate, r, at which the CS is reinforced with the unconditioned stimulus (US). Rats were concurrently trained with four variable-duration CSs with different rs, either as a result of differences in the mean CS-US interval or in the proportion of CS presentations that ended with the US. In each case, R was systematically related to r, and the relationship was very accurately characterized by a hyperbolic function, R = Ar/(r +c). Accordingly, the reciprocal of these two variables-response interval, I (= 1/R), and CS-US interval, i (= 1/r) - were related by a simple affine (straight line) transformation, I = mi+b. This latter relationship shows that each increment in the time that the rats had to wait for food produced a linear increment in the time they waited between magazine entries. We discuss the close agreement between our findings and the Matching Law (Herrnstein, 1970) and consider their implications for both associative theories (e.g., Rescorla & Wagner, 1972) and nonassociative theories (Gallistel & Gibbon, 2000) of conditioning. (PsycINFO Database Record (c) 2011 APA, all rights reserved).     

Effects of conditioned reinforcement frequency in an intermittent free-feeding situation,

Key-pecking intermittently produced a set of brief exteroceptive stimulus changes under two-component multiple schedules of conditioned reinforcement. Throughout the study, free access to grain was concurrently provided on an intermittent basis via a variable-interval tape. Free food presentations scheduled by the tape were delivered if no peck had been emitted for 6 sec, and the brief stimulus changes produced by responding under the multiple schedules were those which accompanied food presentation. The second component of each multiple schedule was always associated with a 1-min, variable-interval schedule of conditioned reinforcement. The schedule associated with the first component was systematically varied and conditioned reinforcement was either absent (extinction) or programmed on a 1-, 3-, 6-, or 12-min variable-interval schedule. Under these conditions, rate of responding in the manipulated component decreased monotonically with a decrease in the frequency of conditioned reinforcement. In addition, contrast effects were often obtained in the constant, second component. These results are similar to those obtained with similar multiple schedules of primary reinforcement.     

Context, observing behavior, and conditioned reinforcement

Pigeons made observing responses for stimuli signalling either a fixed-interval 30-sec schedule or a fixed-ratio x schedule, where x was either 20, 30, 100, 140, or 200 and the schedules alternated at random after reinforcement. If observing responses did not occur, food-producing responses occurred to a stimulus common to both reinforcement schedules. When the fixed-interval schedule was paired with a low-value fixed ratio, i.e., 20 or 30, the presentation of the stimulus reliably signalling the fixed-ratio schedule reinforced observing behavior, but the presentation of the stimulus reliably signalling the fixed-interval schedule did not. The converse was the case when the fixed-interval schedule was paired with a large-valued fixed ratio, i.e., 100, 140, or 200. The results demonstrated that the occasional presentation of the stimulus signalling the shorter interreinforcement interval was necessary for the maintenance of observing behavior. The reinforcement relationship was a function of the schedule context and was reversed by changing the context. Taken together, the results show that the establishment and measurement of conditioned reinforcement is dependent upon the context or environment in which stimuli reliably correlated with differential events occur.     

Uncertainty reduction, conditioned reinforcement, and observing

In a concurrent-chains procedure, pigeons chose between equivalent mixed and multiple fixed-interval schedules of reinforcement. In the first experiment, preference for the multiple schedule was higher when the probability of the shorter fixed interval was less than .50 than for complementary points, an outcome consistent with the delay-reduction hypothesis of conditioned reinforcement and observing, but inconsistent with the uncertainty-reduction hypothesis which requires symmetrical preferences with a maximum when the two intervals are equiprobable. A second experiment assessed preference for equivalent mixed and multiple schedules when each choice outcome resulted in two reinforcements, one on the longer and one on the shorter fixed interval. The order of the two fixed intervals was determined probabilistically. Pigeons again preferred multiple to mixed schedules, although multiple-schedule preference did not vary systematically with the likelihood of the shorter fixed interval occurring first. The results from these choice procedures are consistent with those from the observing-response literature in suggesting that the strength of a stimulus cannot be well described as a function of the degree of uncertainty reduction the stimulus provides about reinforcement.     

Positive conditioned suppression: Transfer of performance between contingent and noncontingent reinforcement situations

Five homing pigeons were trained on concurrent variable-interval schedules. A fixed-duration stimulus was occasionally presented on one key; and, in various conditions, this stimulus terminated (a) without reinforcement, (b) in noncontingent reinforcement, (c) with reinforcement contingent on a response on the key on which the stimulus was presented, and (d) with reinforcement contingent on a response on the key on which the stimulus was not presented. Initially, a stimulus terminating in noncontingent reinforcement generally produced decreased response rates on both keys during the stimulus. Contingencies, however, reliably produced increased rates during the stimulus on the key on which the contingency was arranged, relative to the rate on the concurrently available key. Contingency conditions were followed by noncontingency conditions in which the separation of rates caused by contingencies was maintained. When rates during the stimulus were compared with response rates on the same keys in the absence of the stimulus, contingency-caused rate increases and decreases were again found, but only the rate decreases were maintained in subsequent noncontingency conditions. Further data suggested that the contingency-caused rate changes were not maintained when the stimulus terminated without reinforcement, and that they were unaffected by a threefold decrease in the reinforcement rate provided by the baseline schedules. The results support the suggestion that performance in the positive conditioned suppression procedure results from concurrent and multiple schedule interactions. They further suggest that the production of either acceleration or suppression is dependent on adventitious and historical contingencies.     

Relative frequency of reinforcement and rate of punished behavior

After training on a multiple variable-interval variable-interval schedule of reinforcement, each response in one component of the schedule was followed by a brief electric shock. When the rate of punished responses stabilized, the frequency of reinforcement in the other component was first decreased and then increased from the baseline frequency. The effects of these manipulations were consistent with reports of interactions in multiple schedules involving only unpunished behavior, i.e., the rate of punished responses increased with a higher relative frequency of reinforcement in the punishment component and decreased with a lower relative frequency of reinforcement in that component. The relevance of such findings to a further generality of behavioral contrast effects is discussed.     

Choice and conditioned reinforcement.

A potential weakness of one formulation of delay-reduction theory is its failure to include a term for rate of conditioned reinforcement, that is, the rate at which the terminal-link stimuli occur in concurrent-chains schedules. The present studies assessed whether or not rate of conditioned reinforcement has an independent effect upon choice. Pigeons responded on either modified concurrent-chains schedules or on comparable concurrent-tandem schedules. The initial link was shortened on only one of two concurrent-chains schedules and on only one of two corresponding concurrent-tandem schedules. This manipulation increased rate of conditioned reinforcement sharply in the chain but not in the tandem schedule. According to a formulation of delay-reduction theory, when the outcomes chosen (the terminal links) are equal, as in Experiment 1, choice should depend only on rate of primary reinforcement; thus, choice should be equivalent for the tandem and chain schedules despite a large difference in rate of conditioned reinforcement. When the outcomes chosen are unequal, however, as in Experiment 2, choice should depend upon both rate of primary reinforcement and relative signaled delay reduction; thus, larger preferences should occur in the chain than in the tandem schedules. These predictions were confirmed, suggesting that increasing the rate of conditioned reinforcement on concurrent-chains schedules may have no independent effect on choice.     

Effects on choice of reinforcement delay and conditioned reinforcement

Pigeons chose between fixed-interval schedules of different durations presented in the terminal links of concurrent-chains schedules. The pair of schedules was always in the ratio of 2:1, but the absolute duration of the fixed intervals varied. In one set of conditions, the different terminal-link schedules were associated with different keylight stimuli (cued conditions). In a second set of conditions, the different terminal-link schedules were associated with the same stimulus (uncued conditions). Results from the cued conditions replicated previous findings that preference for the shorter fixed-interval schedule increased with fixed-interval duration. Preferences in the uncued conditions were lower than in the corresponding cued conditions but also increased with fixed-interval length. In addition, the degree of control under the uncued conditions was correlated with the extent to which the schedule during the terminal link was discriminated immediately upon entry into the terminal link. The pattern of results in both conditions was inconsistent with the notion that choice behavior matches relative immediacy of reinforcement. Reanalysis of previous evidence for matching (Chung and Herrnstein, 1967) showed that matching in fact did not occur, as the preferences of their subjects for the shorter of two delays also increased with the absolute size of the delays.     

Response deprivation, reinforcement, and economics

Reinforcement of an instrumental response results not from a special kind of response consequence known as a reinforcer, but from a special kind of schedule known as a response-deprivation schedule. Under the requirements of a response-deprivation schedule, the baseline rate of the instrumental response permits less than the baseline rate of the contingent response. Because reinforcement occurs only if the schedule deprives the organism of the contingent response, reinforcement cannot result from any intrinsic property of the contingent response or any property relative to the instrumental response. Two typical effects of response-deprivation schedules—facilitation of the instrumental response and suppression of the contingent response—are discussed in terms of economic concepts and models of instrumental performance. It is suggested that response deprivation makes the contingent response function as an economic good, the instrumental response as currency.     

Response rate and sensitivity to the molar feedback function relating response and reinforcement rate on VI+ schedules of reinforcement

In 5 experiments, the author examined rats' sensitivity to the molar feedback function relating response rate to reinforcement rate on schedules of reinforcement. These studies demonstrated that, at lower rates of responding, rats' performance on variable ratio (VR), variable interval (VI), and variable interval with linear feedback loop (VI+) schedules was determined largely by reinforcement of interresponse times; response rates were faster on VR than on both VI and VI+ schedules. In contrast, when procedures were adopted to maintain high rates of response, rats showed sensitivity to the molar characteristics of the schedules; they responded as fast on a VI+ schedule as on a VR schedule and faster on both of these schedules than on a yoked VI schedule. When the variance of response rate was manipulated, this factor was noted as an important element in determining sensitivity to the molar characteristics of the schedule.     

Temporal context and conditioned reinforcement value

The effectiveness of a stimulus as a conditioned reinforcer depends on the temporal context of reinforcement, that is, the overall rate of reinforcement in the situation. The dominant view has been that context determines the learned value of a stimulus directly, according to delay-reduction theory. By contrast, the contextual choice model (CCM) maintains that value is independent of context and incorporates the effects of context on choice in the framework of the matching law. The authors report 2 experiments with pigeons as subjects that use transfer tests to assess the value of stimuli in the concurrent-chains procedure. Results strongly support the assumption of CCM that pigeons learn the temporal relations between events independently of context but that context modulates the expression of that learning as choice.     

Preference for conditioned reinforcement.

Pigeons were presented with a concurrent-chains schedule in which both choice alternatives led to the same terminal-link stimulus, which was followed by food. Superimposed on the food-reinforced presentations of the terminal-link stimulus was a second schedule of presentations of the same stimulus that were followed by no food. The absolute number of these no-food stimulus presentations was held constant while their relative frequency assigned to one or the other choice alternative was systematically varied. Preference for a given choice alternative tracked the relative frequency of these stimulus presentations, thus demonstrating that they served as reinforcers. These results resolve conflicts in the literature regarding the effect of conditioned reinforcement on choice.