Multiple Variable-interval Extinction Research Articles

Manual and Ocular Observing Behavior in Human Subjects

The present experiment analyzed manual and ocular observing behavior during a Wyckoff observing-response procedure. Following visual discrimination training with a multiple variable-interval extinction schedule, four human subjects pressed a key to earn points under the corresponding mixed schedule. Subjects could emit a manual response, touching a spot on a computer touchscreen, that produced S+ and S- stimuli correlated with the variable-interval and extinction components, respectively, thus converting the mixed schedule into a multiple schedule. Eye-tracking apparatus measured ocular observing behavior in both multiple and mixed schedules. Under the multiple schedule, subjects tended to look at S+ for longer durations than S-. Under the mixed schedule, in contrast, most subjects manually produced S- for longer durations than S+. Comparisons of the ocular and manual observing responses indicate that direct measurements of eye movements reveal characteristics of observing behavior that do not derive from manual observing responses alone.

Effects of Behavioral History on Resistance to Change

Two experiments examined whether differential resistance to change would occur under identical variable-interval schedules as a function of a differential behavioral history. In Experiment 1, each of 3 pigeons first pecked at different rates under a multiple variable-ratio differential-reinforcement-of-low-rate schedule. In a subsequent condition, a multiple variable-interval variable interval schedule operated in the presence of the same training stimuli, during which there were three 4-session prefeeding probes each occurring during a different stage of training. Pecking generally was more resistant to change in the presence of the stimulus previously correlated with the differential-reinforcement-of-low-rate schedule, and this result was more reliable during the earlier probes. In Experiment 2, each of 3 pigeons first was exposed to a multiple variable-interval extinction schedule, after which a variable-interval schedule replaced extinction. During 3 probes, each conducted during a different stage of multiple variable-interval variable-interval schedule training, food was delivered response independently between components. In the first probe, pecking was more resistant to change for each pigeon under the variable-interval schedule that had been in effect longer, but during the final 2 probes this differential resistance was absent. The present results, therefore, show that under identical schedules a behavioral history can influence resistance to change differentially, but that these history effects tend to dissipate with continued exposure to the identical schedules.

Failure to obtain behavioral contrast when components change after reinforcement

The rate of pecking under the variable-interval component of a multiple variable-interval extinction schedule was investigated as a function of whether the components were changed after reinforcement or were changed on the basis of elapsed time. Behavioral contrast—an increase in the response rate during the unchanged variable-interval component—was observed when the components were changed on the basis of time, but not when the components were changed after reinforcement. These results support the hypothesis that behavioral contrast is primarily a result of selective reinforcement of short interresponse times.

Use of A Multiple Schedule to Evaluate Long-Acting Drugs: Results with Mephenytoin

The utility of a novel procedure to examine a drug’s time course of behavioral action was evaluated. Time- and dose-effect relations for the antiepilepsy drug mephenytoin were examined in pigeons during 12-hr sessions through the use of a multiple variable-interval 60-sec extinction (mult VI EXT) schedule of food delivery. The VI 60-sec components were programmed for the first 10 min of each hr and were followed by 50-min EXT components. Mephenytoin produced dose-dependent decreases in rate of responding; the higher the dose the longer the duration of effect. Peak effects of mephenytoin were observed 2 hr after injection (during the third VI component). At the higher doses drug effects were still evident at the end of the session (i.e., 12 hr after injection). The orderliness of results suggests that, although session length was too short to profile fully the time course of high mephenytoin doses, the present procedure merits further attention by behavioral pharmacologists.

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.

Prefood stimulus effects on an operant discrimination

The effects of superimposing a 60-sec prefood stimulus on a multiple variable-interval extinction schedule of reinforcement were examined with a rat. Response rates in both components increased during the stimulus. There was no evidence of an impairment in discrimination performance, as has been reported with a similar procedure involving a preshock stimulus instead of a prefood stimulus.

Response Interactions in Multiple Schedules: The Influence of Response Displacement

Rats’ lever pressing and wheel running were maintained on concurrently operating variable-interval (VI) schedules of food reinforcement. When the schedule for lever pressing was changed to a multiple VI extinction (EXT) schedule, the probability of lever pressing decreased in EXT and increased in VI (positive behavior contrast). Simultaneously, the probability of wheel running increased in EXT and decreased in VI. Next, the wheel locked either in VI or in EXT. To hold reinforcement parameters constant when the wheel was locked, the schedule for wheel running was changed to response-independent reinforcement on a variable-time schedule. With the wheel locked in VI, the probability of VI lever pressing increased. With the wheel locked in EXT, the probability of wheel running increased in VI, and the probability of VI lever pressing simultaneously decreased resulting in prevention of positive behavior contrast. For one rat, lever pressing and wheel running developed into chained behaviors that were emitted simultaneously, and the results differed for that animal. The experiment shows that positive behavior contrast can depend upon concurrently reinforced behavior, even when reinforcement parameters are unchanged.

Changeover delay effects on topographically tagged discriminative behavior.

In a multiple variable-interval extinction schedule, pigeons' responses on an operant key were differentially reinforced in the presence of discriminative stimuli located on a signal key. Changeover delays of zero, one, two, or four seconds specified the time following a signal-key response within which an operant-key response was not reinforced. Systematic reduction of signal-key response rates with increasing changeover-delay duration indicated that signal-key responding was largely maintained by reinforcement of adventitious signal-key/operant-key response chains.

Differential production of positive and negative discriminative stimuli by normal and retarded children

Using an observing procedure similar to Wyckoff's (1969), two normal and two mentally retarded children were studied. The children were initially trained to earn pennies by pressing a rectangular key according to a multiple variable-interval extinction schedule of reinforcement. After discrimination training, the children were allowed to produce the discriminative stimuli by depressing a second or observing key. The retarded children were different from the normal children in that they produced more of the positive discriminative stimulus (S+) than the negative discriminative stimulus (S−). In the case of the retarded children, S+ observing started high and remained high. In the case of the normal children, S+ observing was initially substantial and then rapidly diminished.

An investigation of peak shift and behavioral contrast for autoshaped and operant behavior.

Instrumental treadle press and nonreinforced key peck responses were monitored during discrimination training and generalization testing in pigeons on positive and negative reinforcement schedules. In Experiment 1, six pigeons pressed a treadle for food on a multiple variable-interval extinction schedule. In Experiment 2, three pigeons pressed a treadle to avoid shock on a multiple free-operant avoidance extinction schedule. Different color keylights signaled S+ and S- components. Some positive behavioral contrast occurred during discrimination training, but the effect was small. Pecking occurred to the S+ keylight in Experiment 1 but not in Experiment 2. On stimulus generalization tests, all subjects displayed a positive peak shift when pressing the treadle for food or to avoid shock. However, peak shift was not found for nonreinforced "autopecks" on the stimulus key, although an area shift was observed in Experiment 1. This is the first demonstration of peak shift for pigeons pressing treadles and the only reliable demonstration of peak shift when negative reinforcement maintained responding. These results, in combination with previous demonstrations of peak shift for rats pressing levers and pigeons pecking keys, indicate that peak shift is a general by-product of operant discrimination learning, since it occurs across a variety of the organisms, responses, and reinforcers.

Stimulus control of topographically tagged responding

Pigeons’ responses on an operant key were reinforced according to either multiple variable-interval variable-interval or multiple variable-interval extinction schedules. The multiple-schedule components were signaled by line-tilt stimuli on a second key (signal key). Signal-key responses never produced reinforcement, and operant-key responses were not reinforced if they followed within 1 sec of a signal-key response. Behavioral contrast was not observed on the operant key, although there was a small, but reliable, increase in signal-key responding in the variable-interval component of the multiple variable-interval extinction condition. Generalization tests were interspersed between sessions of multiple variable-interval extinction training. Generalization gradients along the line-tilt dimension exhibited peak shift for both operant-key and signal-key responding following intradimensional (line tilt) discrimination training. Line-tilt generalization gradients following interdimensional discrimination did not exhibit peak shift. Gradients following intradimensional discrimination were sharper than gradients following interdimensional discrimination for both operant-key and signal-key responding. It was concluded that dimensional stimulus control of topographically tagged responding maintained by the stimulusreinforcer relation parallels that maintained by the response-reinforcer relation.

Behavioral contrast and type of reward: Role of elicited response topography

Groups of pigeons were exposed to multiple variable-interval variable-interval and multiple variable-interval extinction schedules of either food or water reinforcement for keypecking. Discriminative stimuli associated with component schedules were located either on the operant key or on a second “signal” key. When the stimuli were projected on the operant key, positive contrast appeared during discrimination conditions with either food or water as the reinforcer. When the stimuli were projected on the signal key, overall responding to the operant and signal keys showed contrast with food, but negative induction with water as the reinforcer. In the latter condition, the signal for the variable-interval shcedule of water reinforcement elicited a variety of water-related behavior, only some of which was directed at the signal. Thus, the type of reward and location of discriminative stimuli interacted to determine the presence or absence of behavioral contrast effects. In large part, these results support and extend the autoshaping view of contrast.

Positive Contrast in the Rat: A Test of the Additivity Theory

Rats were trained to lever press for food on a multiple variable-interval variable-interval schedule, then shifted to a multiple variable-interval extinction schedule. For six subjects (group L), schedule components were signalled by the presence or absence of a flashing light emitted from an alternate, "signal" lever. For four subjects (group T), schedule components were signalled by two distinct auditory tones. Contrary to the predictions of an additivity theory based on the summation of response classes, contacts on the signal lever did not increase after the schedule shift in group L. However, nine of the ten subjects in the study demonstrated positive contrast effects on the operant lever. In a subsequent test for stimulus control, enhancement and suppression by the discriminative stimuli were found in these same nine subjects. An additivity theory based on the summation of excitatory processes, rather than response classes, appears to account for these data.

INTERACTIONS IN MULTIPLE SCHEDULES: NEGATIVE INDUCTION WITH SQUIRREL MONKEYS1

In Experiment I, lever pressing by squirrel monkeys was maintained under a sequence of variable-interval, multiple variable-interval variable-interval, and multiple variable-interval extinction schedules of food presentation. Negative induction (decreased responding in the unchanged component) occurred when one component of the multiple variable-interval variable-interval schedule was changed to extinction. Negative induction was transient over sessions; responding in the unchanged component usually recovered to a rate similar to that under the multiple variable-interval variable-interval schedule. Negative induction was not accompanied by consistent changes in the patterns of local responding within the unchanged component, and did not depend on whether component schedules were associated with localized (lever lights) or diffuse visual stimuli (houselights), or on whether the unchanged component was a 60- or 180-sec variable-interval schedule. In Experiment II, responding was maintained under a sequence of variable-interval and multiple variable-interval timeout schedules of food presentation. Negative induction occurred when responding declined gradually in the timeout component but not when responding declined abruptly. The nature of interactions in multiple schedules may depend on the species; negative induction was observed with squirrel monkeys under conditions similar to those that produce positive contrast with pigeons.

Behavioral contrast and induction in the crow

Common crows received baseline training on an equal-valued multiple variable-interval variable-interval schedule of food reinforcement. When the schedule was subsequently changed to a multiple variable—interval variable-time schedule, in which reinforcement was delivered independently of responding in the latter component, this resulted in negative induction. That is, responding decreased in both components. After a return to the baseline schedule, a change to a multiple variable—interval extinction schedule, resulted in decreased responding in the extinction component. Accompanying this change was an increase in responding during the unaltered variable—interval component, i.e., positive behavioral contrast. Differences between these findings and predictions derived from several theories of behavioral contrast are discussed.

Operant and Pavlovian factors in cross-response transfer of inhibitory stimulus control

Experiment 1 used a within-response procedure to compare inhibitory stimulus control of the extinction cue in multiple variable interval-extinction ( mult VI EXT) and the variable time cue in multiple variable interval-variable time ( mult VI VT). Experiment 2A made the same comparison using a crossresponse procedure. In addition, Experiment 2A also tested the extinction cue in multiple variable time-extinction ( mult VT EXT), and Experiment 2B tested the variable time cue in mult VT EXT. Unlike the mult VI EXT and mult VI VT conditions, the mult VT EXT condition was administered in the absence of a response manipulandum. The main findings of the present study were: (1) cross-response suppression by the variable time cue in mult VI VT; (2) greater response suppression by the extinction cue in mult VI EXT than by either the variable time cue in mult VI VT or the extinction cue in mult VT EXT; and (3) response facilitation by the variable time cue in mult VT EXT. These findings indicate that inhibitory stimulus control based on an operant source (i.e., absence of an R-S contingency) does transfer across responses, and that such transfer cannot be explained in terms of competing responses. These findings also indicate that operant and Pavlovian sources of stimulus control summate algebraically to determine the inhibitory strength of the extinction cue in mult VI EXT. Finally, the third finding is not consistent with notions that emphasize the importance of location and localization of cues explicitly paired with positive events.

Differential Multiple-Schedule Interactions in Rats

Three experiments examined multiple-schedule interactions in a free-operant paradigm for rats. In Exps. 1 and 2 three rats each and in Exp. 3 five rats were given extended multiple variable-interval baseline training before being shifted to multiple variable-interval extinction. Visual discriminative stimuli and regular extinction, which allowed nonreinforced responding, were used in Exps. 1 and 2, but auditory discriminative stimuli and retraction of the lever to prevent responding during extinction were used in Exp. 3. Positive behavioral contrast was observed in only one out of six rats in Exps. 1 and 2, while negative induction was observed in the other five subjects. However, contrast was observed at some point in training for all five subjects in Exp. 3. The differential multiple-schedule interactions were attributed to the introduction of an additional stimulus-reinforcer dependency with regard to the presence vs absence of the lever in Exp. 3. Results support an autoshaping or additivity account of behavioral contrast.

Signalled Reinforcement and Dimensional Stimulus Control

Summary For four pigeons reinforcement was signalled in one component of a multiple variable-interval 1-min variable-interval 1-min schedule, and two pigeons were trained on a multiple variable-interval 1-min extinction schedule. Following training each bird was given a resistance-to-extinction generalization test, followed by an additional training session, and a final resistance-to-reinforcement generalization test. Test stimuli were combined with presence or absence of the signal. Generalization tests uniformly showed differential dimensional stimulus control in the presence and absence of the signal for three of the four signalled-reinforcement subjects. However, excitatory dimension stimulus control was obtained for the one signalled-reinforcement bird that did not respond differentially during training. Similarly, nondifferential, flat, or inhibitory gradients were obtained for the two extinction subjects. These data support an analysis of signalled reinforcement as a conditional discrimination.

BEHAVIORAL CONTRAST IN THE PIGEON: A STUDY OF THE DURATION OF KEY PECKING MAINTAINED ON MULTIPLE SCHEDULES OF REINFORCEMENT1

Pecks on an operant key were reinforced on either multiple variable-interval variable-interval or multiple variable-interval extinction schedules of reinforcement. The stimuli that signalled the multiple-schedule components were located on a second key (signal key), and a changeover delay prevented reinforcement of signal key-peck-operant key-peck sequences. No behavioral contrast was observed on the operant key, and appreciable responding to the signal key occurred during the variable-interval component of the multiple variable-interval extinction procedure. Peck durations on the signal key were markedly shorter than peck durations on the operant key. Moreover, most responses on the signal key occurred just after the multiple-schedule components changed. These data support an account of behavioral contrast in terms of the summation of pecks that are separately controlled by stimulus-reinforcer and response-reinforcer dependencies, and suggest that the stimulus-reinforcer dependency is responsible primarily for local contrast. In addition, the data suggest that pecks that are controlled by these two dependencies may belong to topographically different classes.

THE CONTROL OF SWITCHING INTO BLACKOUT DURING EXTINCTION1

During the extinction component of a multiple variable-interval extinction schedule, four pigeons learned to peck a second key that switched off the keylights. Two experiments attempted to isolate the events that control this behavior. In the first experiment, switching into blackout was equally maintained when switches were restricted to the first minute as when they were restricted to the last minute of the extinction component. When switches could be emitted in the first and last minutes, they occurred more frequently in the first. Restricting switching to the first minute of each component and eliminating the blackout between components had no effect on switching. In the second experiment, when the stimulus correlated with extinction was omitted, switching decreased slightly. Omission of both multiple schedule stimuli decreased the switching rate, but switching was still maintained. Food reinforcement was then omitted and switching by two birds increased. Switching ceased when blackout was no longer the consequence of pecking the switching key. It was concluded that switching was not controlled by the similarity of the blackouts produced by the switching key and those that occurred between components; nor was it maintained by the temporal proximity of switching responses to the onset of the reinforced component. Finally, switching did not appear to be controlled by the main-key stimuli correlated with the components of the multiple schedule.