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.     

Effect of variable-interval punishment on the behavior of humans in variable-interval schedules of monetary reinforcement

One male and three female human subjects pressed a button for monetary reinforcement under a range of variable-interval schedules specifying different frequencies of reinforcement. On alternate days, responding was also punished (by subtraction of money) according to a variable-interval 170-second schedule. In the absence of punishment, the rate of responding was an increasing negatively accelerated function of reinforcement frequency, as predicted by Herrnstein's equation. The effect of the punishment schedule was to suppress responding under lower frequencies of reinforcement; responding under higher reinforcement frequencies was much less affected. This was reflected in an increase in the value of K_H (the constant expressing the reinforcement frequency corresponding to the half-maximal response rate), whereas there was no significant change in the value of R_max (the constant expressing the maximum response rate). Previous results had shown that variable-ratio punishment resulted in a change in the values of both constants (Bradshaw, Szabadi, and Bevan, 1977). The results of the present study were consistent with the concept that the suppressive effects of punishment on responding depend on the nature of the punishment schedule.     

Force and rate relations in responding during variable-interval reinforcement

Four rats responded on one-minute variable-interval schedules with several variations in peak-force of response required for food reinforcement. Measures of peak force and rate were taken for the responses, which were the downward exertions of force against a static force-transducing operandum. The analysis distinguished responses, a generic class of measured behavior, from criterion responses, an operationally specified subclass required for reinforcement. Absolute rate of response showed no systematic change, but the rate of responses meeting a newly required criterion of peak-force invariably increased through changes in the absolute rate of response, the relative-frequency distributions of peak force, or some combination of both. The relative frequency of responses meeting an elevated force criterion during variable-interval reinforcement exceeded that maintained with the same criterion with continuous reinforcement. The requirement of more effortful responding for reinforcement does not necessarily reduce response rate. Conformity of the behavior to the requirement for reinforcement is the salient effect.     

Synthetic variable-interval schedules of reinforcement

Three pigeons pecked for food on a synthetic variable-interval schedule of reinforcement that had two independent parts: a variable-interval schedule that arranged a distribution of interreinforcement intervals, and a device that randomly assigned each reinforcement to one of 10 classes of interresponse times. The frequencies of reinforcement for the 10 classes of interresponse times were systematically varied, while the overall frequency of reinforcement was held within a comparatively narrow range. The 10 classes extended either from 0.1 to 0.6 sec in 0.05-sec intervals, or from 1.0 to 6.0 sec in 0.5-sec intervals. In the former case, some control by reinforcement was obtained, but it was weak and no simple relationships were discernible. In the latter case, the relative frequency of an interresponse time was a generally increasing function of its relative frequency of reinforcement, and two simple controlling relationships were found. First, the function relating interresponse times per opportunity to reinforcements per opportunity was, over a restricted range, approximately linear with a slope of unity. Second, when all 10 classes of interresponse times were reinforced equally often, the relative frequency of an interresponse time approximately equalled the relative reciprocal of its length.     

Two-key concurrent paced variable-interval paced variable-interval schedules of reinforcement

Nine pigeons were used in two experiments in which a response was reinforced if a variable-interval schedule had assigned a reinforcement and if the response terminated an interresponse time within a certain interval, or class, of interresponse times. One such class was scheduled on one key, and a second class was scheduled on a second key. The procedure was, therefore, a two-key concurrent paced variable-interval paced variable-interval schedule. In Exp. I, the lengths of the two reinforced interresponse times were varied. The relative frequency of responding on a key approximately equalled the relative reciprocal of the length of the interresponse time reinforced on that key. In Exp. II, the relative frequency and relative magnitude of reinforcement were varied. The relative frequency of responding on the key for which the shorter interresponse time was reinforced was a monotonically increasing, negatively accelerated function of the relative frequency of reinforcement on that key. The relative frequency of responding depended on the relative magnitude of reinforcement in approximately the same way as it depended on the relative frequency of reinforcement. The relative frequency of responding on the key for which the shorter interresponse time was reinforced depended on the lengths of the two reinforced interresponse times and on the relative frequency and relative magnitude of reinforcement in the same way as the relative frequency of the shorter interresponse time depended on these variables in previous one-key concurrent schedules of reinforcement for two interresponse times.     

Effect of punishment on human variable-interval performance

Three female human subjects pressed a button for monetary reinforcement in a range of variable-interval schedules specifying different frequencies of reinforcement. On alternate days, responding was also punished (by subtracting money) according to a variable-ratio 34 schedule. In the absence of punishment, rate of responding was an increasing negatively accelerated function of reinforcement frequency; the relationship between response rate and reinforcement frequency conformed to Herrnstein's equation. The effect of the punishment schedule was to suppress responding at all frequencies of reinforcement. This was reflected in a change in the values of both constants in Herrnstein's equation: the value of the theoretical maximum response-rate parameter was reduced, while the parameter describing the reinforcement frequency corresponding to the half-maximal response rate was increased.     

Fixed-ratio punishment by timeout of concurrent variable-interval behavior

Pigeons' responding was maintained by two concurrently available variable-interval reinforcement schedules. A fixed-ratio punishment schedule of timeout periods from the concurrent reinforcement schedules was arranged for responding during one of the variable-interval schedules. The greater the probability of a timeout after a response on the punished variable-interval schedule (the smaller the fixed ratio that produced timeout), the greater the decline in the relative punished response rates. Relative reinforcement rates remained invariant when relative response rates declined. Both behavioral contrast and induction effects were observed on the unpunished variable-interval schedule as a function of timeout punishment of the other schedule.     

Effects of different delay of reinforcement procedures on variable-interval responding

Two experiments studied responding in the rat when the first bar press after a variable period of time produced a cue light that remained on for either 10, 30, or 100 sec and terminated with the delivery of food. In Experiment I, response rate decreased and time to the first response after reinforcement increased as the delay of reinforcement increased. Similar results were obtained whether the delay consisted of retracting the lever during the delay, a fixed delay with no scheduled consequence for responding, or every response during the delay restarted the delay interval. In Experiment II, fixed-delay and fixed-interval schedules of the same duration during the delay period had no differential effect on either response rate or time to the first response after reinforcement, but differentially controlled responding during the delay periods.     

Feedback functions for variable-interval reinforcement

On a given variable-interval schedule, the average obtained rate of reinforcement depends on the average rate of responding. An expression for this feedback effect is derived from the assumptions that free-operant responding occurs in bursts with a constant tempo, alternating with periods of engagement in other activities; that the durations of bursts and other activities are exponentially distributed; and that the rates of initiating and terminating bursts are inversely related. The expression provides a satisfactory account of the data of three experiments.     

The distribution of interresponse times in the pigeon during variable-interval reinforcement

Three pigeons' pecks were reinforced on 1- and 2-min variable-interval schedules, and frequency distributions of their interresponse times (IRTs) were recorded. The conditional probability that a response would fall into any IRT category was estimated by the interresponse-times-per-opportunity transformation (IRTs/op). The resulting functions were notable chiefly for the relatively low probability of IRTs in the 0.2- to 0.3-sec range; in other respects they varied within and between subjects. The overall level of the curves generally rose over the course of 32 experimental hours, but their shapes changed unsystematically. The shape of the IRT distribution was much the same for VI 1-min and VI 2-min. The variability of these distributions supports the notion that the VI schedule only loosely controls response rate, permitting wide latitude to adventitious effects. There was no systematic evidence that curves changed over sessions to conform to the distribution of reinforcements by IRT.     

Percentage reinforcement of fixed-ratio and variable-interval performances

Twenty to seventy per cent of the reinforcements scheduled for pigeons' fixed-ratio 80 performances were replaced by a 4-sec timeout. Pauses after reinforced ratios were unchanged at 80% reinforcement, but were lengthened at lower reinforcement percentages. Pauses after nonreinforced ratios were shorter than post-reinforcement pauses. When 50% of the reinforcements arranged by a variable-interval 60-sec schedule were replaced by a 4-sec timeout, pauses after reinforcement omission increased. Both frustrative nonreward and reinforcement aftereffects notions can explain the fixed-ratio results; neither easily explains the variable-interval data.     

Unsignalled delay of reinforcement in variable-interval schedules

Three pigeons responded on several tandem variable-interval fixed-time schedules in which the value of the fixed-time component was varied to assess the effects of different unsignalled delays of reinforcement. Actual (obtained) delays between the last key peck in an interval and reinforcement were consistently shorter than the nominal (programmed) delay. When nominal delays were relatively short, response rates were higher during the delay condition than during the corresponding nondelay condition. At longer nominal delay intervals, response rates decreased monotonically with increasing delays. The results were consistent with those obtained from delay-of-reinforcement procedures that impose either a stimulus change (signal) or a no-response requirement during the delay interval.     

Development and maintenance of attack in pigeons during variable-interval reinforcement of key pecking

Key-peck responses of two pigeons were maintained on variable-interval schedules of food reinforcement in the presence of a stuffed pigeon to study the characteristics of attack induced by that schedule. The mean interval of the schedule was increased from 15 sec to 600 sec in eight steps before an intermediate interval was reintroduced. The principal characteristics of attack were: (1) substantial attack first occurred on a variable-interval schedule of 90 sec in one pigeon and at 180 sec in the other, (2) the highest attack rates occurred on variable-interval schedules of 300 sec and 600 sec, (3) attack rate generally increased to a maximum and then decreased to a lower level across sessions at each schedule, (4) attacks developed a postreinforcement locus across the initial sessions on all schedules and, except on variable-interval schedules of 300 and 600 sec, occurred primarily in the postreinforcement period during extended training, (5) attack rates and key-peck rates were not recovered when the intermediate-length schedules were reintroduced, and (6) attack rate and key-peck rates were negatively correlated. Except for the fact that the maximum attack rates occurred at interfood intervals of 300 and 600 sec, and that attack and key-peck rates were negatively correlated, these findings have counter-parts in experiments with other reinforcement schedules.     

Behavior of humans in variable-interval schedules of reinforcement

During Phase I, human subjects pressed a button for monetary reinforcement in five variable-interval schedules, each of which specified a different frequency of reinforcement. The rate of responding was an increasing, negatively accelerated function of reinforcement frequency; the data conformed closely to Herrnstein's equation. During Phase II, the same five schedules were in operation, but in addition a concurrent variable-interval schedule (B) was introduced, responses on which were always reinforced at the same frequency. Response rate in component A increased while the response rate in B decreased, as a function of the reinforcement frequency in component A. Relative response rates in the two component schedules matched the relative frequencies of reinforcement. Comparing the absolute response rates in component A during Phase I and Phase II it was found that introduction of the concurrent schedule did not affect the value of the theoretical maximum response rate, but did increase the value of the reinforcement frequency needed to obtain any particular submaximal response rate.     

Fixed-ratio punishment with continuous reinforcement

Rats were reinforced with water for every bar-press and concurrently punished for every 10th or 20th bar-press. Punishment produced an initial suppression of responding followed by recovery. A slight change in the method of delivering punishment eventually led to a high response rate just after punishment, a low response rate just before punishment, and frequent intermediate pauses. The results are interpreted as showing that punishment became a safe signal and that the high rate of responding it released came to act as a conditioned aversive stimulus. The effects of amphetamine were consistent with this interpretation. Alcohol had the paradoxical effect of increasing pauses and depressing the low rate before punishment.     

A comparison of variable-ratio and variable-interval schedules of reinforcement

Four pigeons responded under a two-component multiple schedule of reinforcement. Responses were reinforced in one component under a variable-ratio schedule and in the other component under a variable-interval schedule. It was found that when rates of reinforcement were equal in the two components, the rate of response in the variable-ratio component was nearly twice that in the variable-interval component. Furthermore, for three of the four subjects, the function relating response rate to relative rate of reinforcement in the variable-ratio component had a slope 2.5 to 3 times the slope of the corresponding function for the variable-interval component.     

Local response-rate constancy on concurrent variable-interval schedules of reinforcement

Concurrent variable-interval schedules were arranged with a main key that alternated in color and schedule assignment, along with a changeover key on which a small fixed ratio was required to changeover. Acceptable matching was observed with pigeons in two replications, but there was a tendency toward overmatching. Local response rates were found to differ for unequal schedules of a concurrent pair: local response rate was greater for the variable-interval schedule with the smaller average interreinforcement interval, but qualifications based on an interresponse-time analysis were discussed. In a second experiment, two 3-minute variable-interval schedules were arranged concurrently, and the experimental variable was the changeover procedure: either a changeover delay was incurred by each changeover or a small fixed ratio on a changeover key was required to complete a changeover. Changeover delays of 2 and 5 seconds were compared with a fixed-ratio changeover of five responses. The response output on the main key (associated with the variable-interval schedules) was greater when a changeover delay was arranged than when a fixed ratio was required to changeover. A detailed analysis of stripchart records showed that a 2-second delay generated an increased response rate for 3 seconds after a changeover, while the fixed-ratio requirement generated an increased rate during the first second only, followed by a depressed response rate for 2 seconds.