Second-order avoidance behavior in monkeys

Two monkeys were trained on a three-component multiple schedule using discrete trials. In one component (food), a response terminated a red stimulus and produced food and S(Delta). In the second component (avoidance), a response terminated a green stimulus and avoided shock. In the third component (optional), a response terminated a blue stimulus and produced S(Delta). The consequence of not responding in the blue stimulus, however, was the production of either a food or an avoidance trial. Manipulation of these consequences showed that when food trials were available only a small percent of the time after optional trials, the subjects tended not to respond in the blue, even though this led to an increase in the total number of avoidance trials per day. If only avoidance trials followed as a consequence of not responding in the optional component, the animals terminated the blue stimulus and avoided the avoidance trials. Throughout the experiment both subjects maintained consistently low shock rates (about 10 per day) and these were not affected by the various manipulations. The data suggest that a stimulus associated with avoidance can be a conditioned aversive stimulus and will maintain a more remote avoidance response under certain conditions.     

Maintenance and suppression of responding under schedules of electric shock presentation

In squirrel monkeys previously trained under a continuous avoidance schedule, characteristic patterns of responding were maintained under a 3-min variable-interval schedule of shock presentation (response-produced shock). Responding in the presence of a periodically presented stimulus, the termination of which coincided with the delivery of a response-independent electric shock (Estes-Skinner procedure), was not reliably affected. When shocks followed every response during certain signalled portions of the session, and were presented under the variable-interval schedule during the rest of the session (multiple 1-response fixed-ratio, 3-min variable-interval schedule of shock presentation), responding was suppressed during the fixed-ratio component and maintained during the variable-interval component. Environmental consequences do not have immutable properties, and may either support or suppress behavior, depending on the schedule of presentation.     

Schedules using noxious stimuli. III. Responding maintained with response-produced electric shocks

Responding was maintained in two squirrel monkeys under several variations of a 10-min fixed-interval schedule of electric shock presentation. The monkeys were first trained under a 2-min variable-interval schedule of food presentation, and then under a concurrent schedule of food presentation and shock presentation. In one monkey, when shocks (12.6 ma) followed each response during the last minute of an 11-min cycle ending with a timeout period, responding was increased during the first 10 min and suppressed during the last minute of each cycle. When the shock schedule was eliminated, both the enhancement and suppression disappeared, and a steady rate of responding was maintained under the variable-interval schedule. When the food schedule was eliminated, the shock schedule maintained a characteristic fixed-interval pattern of responding during the first 10 min, but suppressed responding during the last minute of each cycle. The fixed-interval pattern of responding was maintained when the timeout period was eliminated and when only one shock could occur at the end of the cycle. In the second monkey, responding under the concurrent food and shock schedule was suppressed when responses produced shocks after 3-min. Under an 11-min cycle, responding continued to be maintained at increasing shock intensities. When the food schedule was eliminated, a fixed-interval pattern of responding was maintained under a 10-min schedule of shock presentation (12.6 ma). Whether response-produced electric shocks suppressed responding or maintained responding depended on the schedule of shock presentation.     

The effects of stimuli followed by response-independent shock on shock-avoidance behavior

Four rhesus monkeys were trained on a non-discriminated shock-avoidance schedule (baseline). Stimuli followed by response-independent shock were then presented with the avoidance baseline no longer in effect. The main portion of the experiment consisted of superimposing (independently of responding) the stimuli followed by response-independent shock on the avoidance baseline. Different temporal values of stimulus duration and delay of shock (produced by an avoidance response) were presented successively, using each subject as his own control. When the stimulus duration was short or the delay of shock was long, so that avoidance rate during the stimulus could assume any value without resulting in baseline (avoidable) shocks during the stimulus, a lowered or "suppressed" rate of responding developed during the stimulus. When the stimulus duration was long or the delay of shock was brief, so that avoidable shocks resulted from a response decrement during the stimulus, high or "facilitated" rates of responding developed for a large proportion of the time that the stimulus was present.     

Effects of cycle length on performance on a temporally defined avoidance schedule

Three rats were trained on a temporally defined avoidance schedule logically similar to a fixed-interval, limited-hold positive reinforcement schedule. This avoidance schedule was composed of time periods during which responses had no scheduled consequences alternating with time periods during which a response precluded shock. As with fixed-interval length and response rate on positive reinforcement schedules, an inverse relationship was obtained between the length of the no-consequence interval and response rate during the no-consequence interval. An inverse relationship was also obtained between the length of the no-consequence interval and the per cent of shocks avoided. A rate increase within the no-consequence interval, similar to that typically produced by fixed-interval positive reinforcement procedures, was displayed by one of the rats where the no-consequence interval was at intermediate values and frequency of shock was relatively high. The introduction of a discriminative stimulus correlated with the avoidance interval produced typical discriminated avoidance behavior as well as alterations in temporal patterning of responses during the no-consequence interval in the two rats exposed to this procedure. These alterations in temporal patterning disappeared when the discriminative stimulus was removed. The results were consonant with those reported in the literature involving food reinforcement and fixed-interval, limited-hold schedules.     

Avoidance response rates during a pre-food stimulus in monkeys

Free-operant avoidance responding was maintained by a shock avoidance schedule in three monkeys. The frequency of avoidance responses during a stimulus terminated by response-independent food pellet presentation was dependent upon the method of pellet delivery. Avoidance rates were relatively increased when food retrieval responses followed pellet delivery. Avoidance rates were decreased when retrieval responses preceded pellet delivery.     

Drug-behavior interaction history: modification of the effects of morphine on punished behavior.

Squirrel monkeys were trained to respond under a multiple fixed-interval, fixed-interval schedule in which the first response after 5 min terminated a visual stimulus in the presence of which electric shocks could occur. During one component of the schedule, correlated with one color of stimulus lights, every 30th response also produced electric shock; responding was suppressed during this component to approximately 10 to 12% of that occurring in the alternate component in which responding was not punished. In contrast to previous research, morphine (0.03 to 1.0 mg/kg) increased punished responding. Unpunished responding, however, was either not affected or decreased at doses of morphine that increased punished responding. Increases in rate of punished responding also occurred when the single-schedule punishment condition was studied alone in these animals. Subsequent experimentation, which systematically analyzed the development of the rate-enhancing effects of morphine on punished responding, involved the study of drug effects in additional monkeys trained initially under a single-schedule punishment condition. The effects of morphine on punished responding were studied before, after, and then during exposure to the multiple schedule that included a component in which responding was not punished. Increases in response rate with morphine did not occur until it was administered during exposure to the multiple schedule that included a component in which responding was not punished. As with the other monkeys, once the rate increases in punished responding occurred under the multiple schedule, these effects of morphine persisted, even when the multiple schedule was removed.(ABSTRACT TRUNCATED AT 250 WORDS)     

The relative aversiveness of signalled vs unsignalled avoidance

Subjects avoided shock by pressing on one lever under an unsignalled condition, but by pressing a separate lever they changed the condition to signalled avoidance for 1-min periods. Signalled avoidance periods were identified by a correlated stimulus. All eight subjects responded to change the unsignalled schedule to a signalled one. Once contact with signalled avoidance was made, subjects continued responding to remain in that condition. Other tests showed that changeover responding was greater when the correlated stimulus was presented without the signal than when the signal was presented without the correlated stimulus. An analysis based upon shock and shock-free periods is presented.     

Actual versus potential shock in making shock situations function as negative reinforcers

The relative importance of potential and actual shocks in making shock situations function as negative reinforcers was studied. Shocks were scheduled to occur at the same rate during two stimuli. During one, squirrel monkeys could avoid the shocks; during the other, they were unavoidable. For the two stimuli the potential rate of shocks was the same, but the actual rate was lower during avoidance because of avoidance responding. Fixed-ratio responding was maintained by the change from unavoidable shock to avoidance, indicating that the change was reinforcing when it resulted in a reduction in actual shock rate with no reduction in potential shock rate. Further increases in the rate of potential shock during avoidance had little effect upon the fixed-ratio responding until the rate was increased to the point that the actual shock rate during avoidance was comparable with that during unavoidable shock. At that point, the fixed-ratio response rate decreased nearly to zero. These findings show that actual shocks are more important than potential shocks in determining whether or not a shock situation will function as a negative reinforcer; this explains why the change from unavoidable shock to avoidable shock is reinforcing.     

Second-order optional avoidance as a function of fixed-ratio requirements

Two rhesus monkeys responded on a fixed-ratio schedule in Stimulus 1 (blue light) to avoid the onset of Stimulus 2 (green light). Failure to avoid Stimulus 2 required a second fixed-ratio performance to avoid Stimulus 3 (red light) in the presence of which unavoidable shock occurred. Relative frequencies of avoidance performance in the blue light and in the green light were inversely related to the ratio requirement under each stimulus condition. Both differential response-cost and avoidance-failure probability factors were related to the observed changes.     

Transfer of control of the pigeon's key peck from food reinforcement to avoidance of shock

Eight pigeons were initially trained to peck a white key for food under a variable-interval 1-min schedule of reinforcement. Then, a shock-avoidance schedule was initiated and food was no longer available in the experimental situation. Under the avoidance schedule, each peck on the key postponed shock for 40 sec. A warning signal, consisting of tone and red houselights, was presented after 30 sec without a response. If no response occurred, a shock was delivered 10 sec after warning-signal onset. Shocks were delivered every 10 sec in the presence of the warning signal until a response was made. The warning signal was terminated only by a response. Key pecking of all eight pigeons came under control of the avoidance schedule and responding continued throughout the 20-day avoidance training period.     

Generalization of excitation and inhibition after different amounts of training of an avoidance baseline

After acquisition of a treadle-pressing response maintained by an avoidance contingency, four groups of pigeons received interdimensional discrimination training. For two groups, the positive stimulus was a 1000-Hertz tone correlated with the avoidance schedule and the negative stimulus was noise correlated with extinction. The discriminative stimuli were reversed for the other two groups. For two groups, the test stimuli were presented during extinction without any shocks during the test stimuli, for the other two groups, an unavoidable shock was presented during each test stimulus. Generalization was measured daily during discrimination training by randomly substituting each of six test frequencies for the 1000-Hertz tone. When the 1000-Hertz tone was correlated with the avoidance schedule, the number of responses to it increased and the excitatory gradient became steeper as a function of the amount of training. When the 1000-Hertz tone was associated with extinction, the number of responses to it decreased as a function of days of training and the inhibitory gradient became slightly steeper, provided that responding to the test stimulus was elevated by unavoidable shock. The training effects parallel those obtained with positive reinforcement.     

Variable-interval schedules of timeout from avoidance

Rats were trained on concurrent schedules in which pressing one lever postponed shock and pressing the other occasionally produced a 2-min timeout during which the shock-postponement schedule was suspended and its correlated stimuli were removed. Throughout, the shock-postponement schedule maintained proficient levels of avoidance. Nevertheless, in Experiment 1 responding on the timeout lever was established rapidly, was maintained at stable levels on variable-interval schedules, was extinguished by withholding timeout, was reestablished when timeout was reintroduced, and was brought under discriminative control with a multiple variable-interval extinction schedule of timeout. These results are in contrast with Verhave's (1962) conclusion that timeout is an ineffective reinforcer when presented to rats on intermittent schedules. In Experiment 2 the consequence of responding on the timeout lever was altered so that the shock-postponement schedule remained in effect even though the stimulus conditions associated with timeout were produced for 2 min. Responding extinguished, indicating that suspension of the shock-postponement schedule, not stimulus change, was the source of reinforcement. By establishing the reinforcing efficacy of timeout with standard variable-interval schedules, these experiments illustrate a procedure for studying negative reinforcement in the same way as positive reinforcement.     

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.     

Concurrent performances: a baseline for the study of conditioned anxiety

Three rats were trained to lever press on concurrent random interval 2-min random interval 2-min schedules of milk reinforcement. With a 5-sec changeover delay, relative response rate matched the relative reinforcement duration associated with each lever. A stimulus, during which unavoidable shocks occurred at random intervals, was superimposed on this concurrent baseline, and shifts in preference were found. However, data from this procedure were ambiguous, apparently confounded by shock-elicited response bursts. Termination of the shocks during the stimulus resulted in a rapid recovery of matching, which was preceded by a brief facilitation of responding on the less-preferred lever. The procedure was then changed to a conventional conditioned anxiety paradigm with a variable duration pre-shock stimulus. A marked shift in relative response rate towards the preferred lever was found in all three rats; that is, responding on the preferred lever was far less suppressed during the pre-shock stimulus than responding on the less-preferred lever.     

Responding in the cat maintained under response-independent electric shock and response-produced electric shock

Key-pressing responses in the cat were maintained under conditions in which brief electric shock was first postponed by responses (avoidance), then periodically presented independently of responses, and finally produced by responses on a fixed-interval schedule of 15 min (FI 15-min). A steady rate of responding occurred under shock avoidance and under response-independent shock; positively accelerated responding was engendered by the FI 15-min schedule. A second experiment studied responding under second-order schedules composed of three FI 5-min components. Responding was suppressed when a stimulus was presented briefly at completion of each FI 5-min component and a shock followed the brief stimulus at completion of the third component. Responding was maintained when each of the first two components was completed either with or without presentation of a brief stimulus and a shock alone was presented at completion of the third FI 5-min component.     

Responding under schedules combining response-dependent and response-independent shock delivery

Lever pressing of three squirrel monkeys with experience under continuous avoidance schedules was maintained by response-produced shock under a 5-minute variable-interval schedule. Responding decreased when half of the scheduled shocks were delivered independently of lever pressing and decreased further when all shocks were independent of lever pressing. Responding was lowest when all shocks were eliminated. When the proportion of response-dependent shocks increased, responding increased. This relation occurred even though the frequency and temporal distribution of shock delivery remained the same. Responding of two monkeys increased in a graded fashion as the frequency of shock was increased by arranging variable-time 5-minute, 2-minute, and 1-minute schedules jointly with the variable-interval 5-minute schedule. Thus, increasing the proportion of response-independent shocks decreased responding when the overall frequency of shocks stayed the same, but increased responding when the overall frequency of shock delivery increased.     

Conditioned suppression of drl responding: Effect of ucs intensity, schedule parameter, and schedule context

In Experiment I, groups of rats were trained to press a lever for food reinforcement on differential reinforcement of low rate (DRL) schedules which differed in parameter value. A stimulus which terminated with either a 0.5-mA or 2.0-mA electric shock was then superimposed upon each DRL baseline. In general, the magnitude of conditioned suppression was an inverse function of DRL schedule parameter and a direct function of shock intensity. Experiment II demonstrated that the rate of responding maintained by the DRL component of a multiple DRL-extinction schedule decreased during a stimulus preceding a 0.5-mA shock, whereas the rate of responding maintained by the DRL component of a multiple DRL-variable interval schedule showed little change or increased slightly during a stimulus preceding a 0.5-mA shock.     

Avoidance extinction in goldfish

Independent groups of goldfish trained to avoid shock in a shuttlebox situation were presented with several extinction procedures in which the relationships between the conditioned stimulus and shock were altered and/or response contingencies removed. Random shock presentations, equivalent to the number of shocks received during avoidance acquisition, resulted in response decrements similar to those obtained when the conditioned stimulus was presented alone. Pairing the conditioned stimulus with shock on every trial, however, served to maintain response levels. When response-contingent punishment was superimposed upon these Pavlovian pairings, performance was facilitated slightly although punishment alone resulted in somewhat faster response reduction than that produced by exposure only to the conditioned stimulus. Extinction of avoidance responding produced by exposure to the conditioned stimulus alone was dependent on the total duration of exposure and independent of both number of stimulus onsets and response prevention. These experiments demonstrated that, in general, the procedures used to reduce avoidance responding in rats were equally effective for goldfish, with one exception: the introduction of a Pavlovian contingency following avoidance acquisition, making the previously avoidable shock unavoidable, maintained response probabilities near previously established levels.     

Autonomic concomitants of discriminative avoidance and punishment training in the monkey

TwoCebus albifrons monkeys were trained to press a back-lighted panel to postpone a brief electric shock to the tail using a Sidman avoidance schedule (SS = 40 sec, RS = 40 sec). After 25 training sessions, a discriminative schedule was introduced, with the Sidman avoidance continuing in the presence of one discriminative stimulus and punishment introduced in the presence of the other. The discriminative stimuli were colors on the panel. Discriminative training also involved 25 sessions, each with a random sequence of 6 avoidance and 6 punishment segments, with 30 sec intervals between the segments. Plantar skin conductance and heart rate were recorded along with the panel-pressing behavior. The two monkeys adjusted to the discriminative schedule quite differently from one another. One animal responded at a high level and avoided very well (during avoidance) but was punished frequently (during punishment). The other animal responded less frequently and received many shocks during avoidance but almost none during punishment. The animal that showed less ability to inhibit responding (and received about four times as many shocks overall) appeared to have discriminated better temporally in spacing its responses during avoidance training. The monkey whose panel-pressing behavior resulted in more shocks also tended to show a higher tonic level of autonomic arousal. However, within-animal differences in shock frequency (between avoidance and punishment) were not similarly related to autonomie arousal. The animal that received fewer shocks overall (but more during avoidance) showed greater arousal during punishment. The animal that received more shocks overall (but fewer during avoidance) showed no arousal differences between avoidance and punishment.