Some aspects of self aversive stimulation in the hooded rat

Three hooded rats were trained to bar press for variable-ratio liquid reinforcement after which an electric shock was delivered following the response. Initially, the shock was presented on a FR 100 basis but the frequency was gradually increased until all responses were punished. Finally, a partial extinction procedure was conducted to determine if the shock resulted in increased bar pressing. No durable suppression of responding occurred, although one subject's rate was reduced during continuous shock. The overall trend for the three animals was one of increased responding. Changes in the pattern of responding were also observed suggesting that the suppressive effects of the punishment were largely restricted to the first response following reinforcement. Increased responding as a function of shock reintroduction during extinction was also observed.     

The effect of punishment shock intensity upon responding under multiple schedules

In the first of two experiments, responses of two pigeons were maintained by multiple variable-interval, variable-ratio schedules of food reinforcement. Concurrent punishment was introduced, which consisted of a brief electric shock after each tenth response. The initial punishment intensities had no lasting effect upon responding. Then, as shock intensity increased, variable-ratio response rates were suppressed more quickly than variable-interval response rates. When shock intensity decreased, variable-interval responding recovered more quickly, but the rates under both schedules eventually returned to their pre-punishment levels. In the second experiment, the following conditions were studied in three additional pigeons: (1) With each shock intensity in effect for a number of sessions, punishment shock intensity was gradually increased and decreased and responding was maintained by multiple variable-ratio, fixed-ratio schedules of food reinforcement; (2) Changes in punishment shock intensity as described above with responding maintained by either a variable-ratio or a fixed-ratio schedule, which were presented on alternate days; (3) Session-to-session changes in shock intensity with responding maintained by multiple variable-ratio, fixed-ratio schedules. Responding under the two schedules was suppressed to approximately the same extent by a particular shock intensity. Also, post-reinforcement pauses under the fixed-ratio schedule increased as response suppression increased.     

Characteristics and response-displacement effects of shock-generated responding during negative reinforcement procedures: pre-shock responding and post-shock aggressive responding

Bar-pressing (Experiment I) or key-pressing (Experiments II and III) responses of monkeys were reinforced according to a fixed-interval schedule of negative reinforcement: the first response after a fixed interval of time terminated regularly spaced shocks for a fixed time designated as the reinforcement period. During extinction, shocks continued during the reinforcement period. That there were two types of responding generated by shock alone was indicated by (1) the level of responding maintained during extinction relative to conditions without shock, (2) the stability of two between-shock response patterns across reinforcement and extinction conditions, and (3) the development of these two between-shock patterns without a history of reinforcement. Subjects developed either a pre-shock or a post-shock response pattern when only the bar was available. However, when both a bite tube, an operandum requiring an aggressive topography, and a recessed key, an operandum that did not require an aggressive topography, were provided, the post-shock pattern was observed in tube biting and the pre-shock pattern was observed in key pressing. Removal of the bite tube produced post-shock key responding similar to that observed when only the bar was available. The displacement of post-shock, aggression-motivated responding confirmed the confounding effect of shock-generated responding in negative reinforcement procedures, and suggests that the use of concurrent response alternatives would reduce such confounding.     

Punishment of temporally spaced responding

The responses of pigeons were maintained by a DRL schedule of food reinforcement. With this schedule, responses were reinforced only when a fixed period of time elapsed without an intervening response. Punishment of all responses reduced the frequency of these responses as a direct function of the punishment intensity. As a consequence of the increased temporal spacing of responses, more reinforcements resulted during punishment. Under progressively higher intensities of punishment, the reinforcement frequency increased to a maximum value and then decreased at the highest intensities. The increased frequency of reinforcement which resulted during punishment did not counteract the suppressive effect of punishment, nor did it lead to a low response rate after punishment was removed. Punishment did not reduce the inter-response time distribution uniformly, but rather especially reduced the number of short inter-response times. Even at the low punishment intensities, the number of short inter-response times was considerably reduced. After punishment was discontinued, performance recovered almost completely after a compensatory burst. The number as well as the temporal pattern of responses returned to normal.     

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.     

SOME RELATIONS BETWEEN CLASSICALLY CONDITIONED AGGRESSION AND CONDITIONED SUPPRESSION IN SQUIRREL MONKEYS

During three experiments with squirrel monkeys, stimulus and shock pairings were given in the presence of a bite tube. Experiments 1 and 2 used a conditioned-suppression procedure in which bar pressing was reinforced with food. A transparent shield prevented biting of the bar. When the stimulus was paired with shock, bar pressing decreased (conditioned suppression) and tube biting increased during the stimulus (classically conditioned aggression). When the bite tube was removed on alternate sessions in Experiment 2, there was more suppression when the tube was present, thus suggesting that biting competed with bar pressing. However, this simple competing-response interpretation was complicated by the findings of Experiment 3 where, with naive monkeys, bar pressing was never reinforced with food, yet bar pressing was induced during the stimulus and was highest when the bite tube was absent. The fact that stimulus-induced bar pressing developed indicates that bar pressing in conditioned-suppression procedures, suppressed or not, may be maintained by two types of control—the food reinforcer and induced CS control. The higher rate of induced bar pressing during the stimulus with the bite tube absent confounds a simple competing response interpretation of conditioned suppression. It suggests that shock-induced responses during conditioned suppression could be both contributing to and competing with responding maintained by food, with the net effect depending on specific but ill-defined features of the situation.     

Toward a quantitative theory of punishment

In two experiments, pigeons' key pecking for food on concurrent variable-interval schedules was punished with electric shock according to concurrent variable-interval punishment schedules. With unequal frequencies of food but equal rates of punishment associated with the two keys and at several intensities of shock, the response and time allocation of all six pigeons overmatched the obtained relative frequency of food. The overmatching was predicted by a subtractive model of the interaction between punishment and positive reinforcement but not by two alternative models. Increases in the k and r_e parameters of the generalized matching law could not account for the observed shifts in preference.     

Suppression of operant behavior and schedule-induced licking in rats

The first experiment studied the effects of punishment on rats' lever pressing maintained by a fixed-interval schedule of food reinforcement and on the associated schedule-induced licking. When licking was followed by shock, licking was suppressed but lever pressing was largely unaffected. When lever pressing was followed by shock, lever pressing was suppressed but licking was unaffected. In both cases, the punished behavior recovered its previous unpunished level when the shocks were discontinued. In a second experiment, the rats' lever pressing was maintained by a variable-interval schedule of food reinforcement under which polydipsic licking also developed. Both lever pressing and licking were partially suppressed during a stimulus correlated with occasional unavoidable electric shocks. With a higher shock intensity, both behaviors were suppressed further. Both lever pressing and licking recovered their previous levels when shocks were discontinued. These results show that schedule-induced licking, which has been described as adjunctive behavior, can be suppressed by procedures that suppress reinforced lever pressing, an operant behavior.     

Punishment of an extinguishing shock-avoidance response by time-out from positive reinforcement

Two experiments were conducted to determine the effects of punishment by time-out from positive reinforcement on the extinction of discriminated shock-avoidance responding. Subjects were trained initially to bar press for food on an intermittent schedule of reinforcement and, concurrently, to avoid shock at the onset of a warning signal. Experiment I compared avoidance extinction performance under no punishment and when avoidance responding resulted in a 30-sec TO from reinforced appetitive responding. In Exp II, the contingent use of TO punishment was compared with its random, or noncontingent use. The results of both experiments showed that in the absence of punishment, avoidance extinction was characterized by short latencies and nearly 100% avoidance responding. Avoidance responding in extinction was little affected by noncontingent TO punishment. When TO was made contingent upon avoidance responding, however, avoidance latencies immediately increased and the frequency of avoidance responses subsequently decreased to zero.     

A ROLE FOR NEGATIVE REINFORCEMENT OF RESPONSE OMISSION IN PUNISHMENT?

This experiment attempted to disentangle response-rate reductions controlled by the direct suppressive effects of a punisher from those due to negative reinforcement of response omission. Key-peck responding of pigeons was maintained by a conjoint variable-interval 3-min schedule of food presentation variable-interval 30-s schedule of response-dependent electric shock presentation. Omission of responses for 5, 10, or 30 s resulted in the possibility of canceling a scheduled shock. Response rates were a function of required pause duration, with lower rates occurring when longer periods of response omission were required for shock cancellation. These results show that, with several parameters of punishment held constant, response rates were controlled by the negative reinforcement contingency. Such a finding argues for renewed consideration of the role of negative reinforcement in punishment contingencies.     

Predator videos and electric shock function as punishers for zebrafish (Danio rerio)

Zebrafish (Danio rerio) are a promising animal model for studying the effects of gene–environment interactions on behavior. Two experiments were conducted to assess punishment effects of presenting predator videos (Indian leaf fish; Nandus nandus) and electric shock on operant approach responses in zebrafish. In Experiment 1, the predator video and shock stimuli were presented upon a response maintained by a single variable‐interval schedule of food reinforcement in different groups of fish. In Experiment 2, the predator video and shock stimuli were presented upon one of two response alternatives maintain by concurrently available variable‐interval schedules of food reinforcement in different groups of fish. Responding decreased when the predator video and shock stimuli were presented relative to their absence in both experiments. Moreover, responding on an unpunished alternative did not reliably decrease in Experiment 2. These results indicate that the decrease in responding resulted from the punishment contingency rather than from elicited species‐specific defense responses or conditioned avoidance. Thus, the predator video and electric shock functioned as punishers of operant behavior for zebrafish. Identifying punishers for this species could lead to research on how gene–environment interactions influence individual differences in sensitivity to punishment.     

Summation of punishment suppression

In two experiments, eight rats were trained to lever press with food on a variable-interval schedule. Bar pressing produced shock on a variable-interval schedule in the presence of two independently presented stimuli, a light and a tone. Two rats in each experiment received alternative presentations of the light and the tone and were consequently always in the presence of a stimulus that signalled variable-interval punishment. The other two rats in each experiment were treated similarly except that they received periods in which neither light nor tone was present. During these periods, bar pressing was not punished. The two stimuli that signalled punishment were then presented simultaneously to evaluate the effect of stimulus compounding on response suppression. The subjects trained without punishment-free periods did not show summation to the compound stimulus; the subjects trained with punishment-free periods showed summation of suppression. The major difference between the two experiments was the longer mean interval of variable-interval punishment used in the second experiment. This manipulation made the summation effect more resistant to extinction and thus increased its magnitude.     

Punishment and rate of positive reinforcement

This experiment investigated the effect of several punishment intensities on two responses maintained by contrasting rates of reinforcement. The responses were concurrently reinforced according to two different variable-interval schedules. Because these schedules were independent of one another and programmed different rates of reinforcement, the two responses occurred at dissimilar rates. When responses were simultaneously suppressed by punishment, both rates were reduced proportionately until suppression was virtually complete. In other words, the per cent suppression resulting from punishment was independent of the rate at which the response was reinforced. Phenomena found in single-response studies were duplicated here. Responding tended to increase both within and between punishment sessions at mild and moderate punishment intensities. Cessation of punishment led to a "compensatory" overshooting beyond the prepunished response rate.     

An interresponse time analysis of variable-ratio punishment

An interresponse time analysis was used to study the effects of variable-ratio punishment schedules on the temporal pattern of reinforced responding. Twelve pigeons responded on a baseline variable-interval schedule of food reinforcement. A variable-ratio ten schedule of electric shock punishment was then introduced. The shock intensity was systematically increased to the highest intensity at which responding could be maintained. At this intensity, the mean variable-ratio value was increased and then decreased. Variable-ratio punishment resulted in an increased relative frequency of very short unreinforced interresponse times (response bursting). Increased response bursting accounted for instances of response rate facilitation. In addition, shock was followed by interresponse times of decreasing mean length over the first several responses after shock.     

Reversal of preference under progressive-ratio schedules by punishment

A progressive-ratio reinforcement schedule, in which successive reinforcements required an additional 50 responses, was programmed on one key. A response on a second key reset the progressive-ratio schedule to the first step. Before punishment, all pigeons consistently reset the schedule after reinforcement on the first step, thereby minimizing the number of responses required for reinforcement. Punishment was a brief electric shock contingent upon each response on the reset key. The first effect of punishment was to change the frequency of extra responses on the reset key. Under higher intensities of punishment, the pigeons completed the advanced steps of the progressive-ratio schedule before resetting to the first step. Completions of advanced steps were accompanied by decreases in the overall rate of responding and the rate of reinforcement. When the punishment contingency was removed, the major features of pre-punishment performance were recovered.     

Visual evoked potential augmenting/reducing slopes in cats—2. Correlations with behavior

Relationships were studied in cats between the augmenting/reducing slopes of visual evoked potentials (VEP) and three types of behavioral responses: learning and performance measures in (1) fixed interval (FI), and (2) differential reinforcement of low rate of response (DRL) bar pressing tasks for food reward, and (3) the effect of noise stress or increasing task difficulty on performance of an FI, DRL or 2 bar discrimination task. The most reliable slope measure (N1 at a medium intensity range) was found to correlate most highly with inhibitory behaviors such that reducers were most successful in controlling bar pressing behavior during an inhibitory DRL task or when stress was introduced. At a higher range of flash intensity slopes tended to be more negative, and the P1 - N1 slopes although more variable correlated most consistently with general temperament. Augmenters at a high intensity range were more active and explaratory, and learmed to bar press more quickly and efficiently.     

Motivational aspects of escape from punishment

Punishment and escape were studied simultaneously by allowing a subject to escape from a stimulus situation in which responses were punished, into a stimulus situation in which responses were not punished. The frequency of the punished responses was found to be an inverse function of the intensity of punishment, whereas the frequency of the escape response was a direct function of the intensity of punishment. Both of these functions were obtained under three different schedules of food reinforcement. The strength of the escape behavior was evidenced by (1) the emergence of the escape response even when the frequency of food reinforcement decreased as a consequence of the escape response, (2) the maintenance of the escape response by fixed-interval and fixed-ratio schedules of escape reinforcement, and (3) the occurrence of escape responses at intensities of punishment that otherwise produced only mild suppression of the punished response when no escape was possible. This last finding indicates that a subject may be driven out of a situation involving punishment even though the punishment is relatively ineffective in suppressing the punished responses when no escape is possible.     

An extinction-induced increase in an aggressive response with humans

Nine subjects, 14 to 18 yr old, pulled a knob on a schedule of monetary reinforcement. Concurrently, they escaped or avoided periodic presentations of a tone by pressing a button that required 1.5 lb (6.67 N) of force or by punching a padded cushion that required 20 lb (88.96 N) of force. The punching response was designated as an aggressive response because the force of this response together with its topography was comparable to responses of humans that deface objects and produce escape or counter aggression from other humans. It was found that button pressing was the preferred concurrent avoidance response and there were few punches. However, when the monetary reinforcer was discontinued (extinction) punching increased for seven of the nine subjects, but there was no consistent change in the rate of button pressing. When the punching response was replaced by another non-preferred but non-aggressive response, neither this response nor button pressing increased during extinction. Hence, the increase in punching during extinction cannot be attributed solely to the fact that it was a concurrent response or a non-preferred response.     

Two types of pigeon key pecking: suppression of long- but not short-duration key pecks by duration-dependent shock

The key pecking of eight pigeons was maintained on a variable-interval 1-minute schedule of food reinforcement. Sometimes, all responses between 35 and 50 milliseconds in duration produced a shock; sometimes, all responses between 10 and 25 milliseconds produced a shock; sometimes, shocks were produced by pecks without regard to duration (nondifferential punishment), and sometimes shocks were delivered independently of responding. Punishment of 35- to 50-millisecond responses selectively suppressed those responses, while punishment of 10- to 25-millisecond responses and nondifferential punishment suppressed responding overall but did not suppress responses of particular duration. Punishment of 35- to 50-millisecond responses suppressed key pecking slightly less than did nondifferential punishment. Punishment of 10- to 25-millisecond responses and response-independent shock produced roughly equal amounts of suppression, substantially less than the other punishment procedures. The data support the view that there are at least two kinds of key peck, identifiable on the basis of duration, one of which (short duration) is insensitive to its consequences.     

Extinction of a heterogeneous chain after several reinforcement schedules

Rats were conditioned to emit the following two-member chain of responses on two different operanda always available: responses on a vertical bar produced a discriminative stimulus for food-reinforced responding on a horizontal bar. Responses on the vertical bar produced a discriminative stimulus on a variable-interval 1-min schedule, and the horizontal bar produced food on a variable ratio of 10 responses. Control conditions were included in which vertical bar responses were also food-reinforced simultaneous with the onset of the discriminative stimulus for the horizontal bar response and a tandem schedule which had the same response requirements but without different exteroceptive stimuli associated with the separate components of the response chain. The latter condition greatly retarded acquisition of the response chain compared to the other schedules studied here and compared to reports in the literature on homogeneous (single operandum) response chains. Intermittent reinforcement of the chain led to greater resistance to extinction of both members and the chain remained intact longer in the sense that stimulus control was maintained.