Interresponse Time Distributions Research Articles

STEADY‐STATE PERFORMANCE ON FIXED‐, MIXED‐, AND RANDOM‐RATIO SCHEDULES

Three groups of rats pressed a lever for milk reinforcers on various simple reinforcement schedules (one schedule per condition). In Group M, each pair of conditions included a mixed-ratio schedule and a fixed-ratio schedule with equal average response:reinforcer ratios. On mixed-ratio schedules, reinforcement occurred with equal probability after a small or a large response requirement was met. In Group R, fixed-ratio and random-ratio schedules were compared in each pair of conditions. For all subjects in these two groups, the frequency distributions of interresponse times of less than one second were very similar on all ratio schedules, exhibiting a peak at about .2 seconds. For comparison, subjects in Group V responded on variable-interval schedules, and few interresponse times as short as .2 seconds were recorded. The results suggest that the rate of continuous responding is the same on all ratio schedules, and what varies among ratio schedules is the frequency, location, and duration of pauses. Preratio pauses were longer on fixed-ratio schedules than on mixed-ratio or random-ratio schedules, but there was more within-ratio pausing on mixed-ratio and random-ratio schedules. Across a single trial, the probability of an interruption in responding decreased on fixed-ratio schedules, was roughly constant on random-ratio schedules, and often increased and then decreased on mixed-ratio schedules. These response patterns provided partial support for Mazur's (1982) theory that the probability of instrumental responding is directly related to the probability of reinforcement and the proximity of reinforcement.

The local organization of behavior: dissociations between a pigeon's behavior and self-reports of that behavior.

The purpose of the experiment was to study the relation between what an organism does in a setting that demands temporal patterning of behavior and what it reports it has done. More specifically, a pigeon produced two classes, shorter and longer, of temporal patterns of key pecks (interresponse times) on a center key. Occasionally, a symbolic matching-to-sample probe arranged on side keys asked the pigeon whether its most recent pattern was a shorter or longer one. The longer reinforced pattern was always three times as long as the shorter one and the two patterns were reinforced equally often. Absolute duration of reinforced patterns was varied. In some conditions, interresponse-time distributions on the center key were bimodal, indicating a clear behavioral adaptation to the contingency, yet a bird did not report very well by appropriate side-key responding what its most recent interresponse time had been. In other conditions, the interresponse-time distributions were less clearly bimodal, yet a bird reported more accurately its previous interresponse time as shorter or longer. Thus, there was a dissociation between how well behavior on the center key conformed to the schedule requirement and how well a bird reported what it was doing on the center key. In addition, as absolute duration of the reinforced patterns was increased, a bird categorized its most recent pattern less well even as its preference for the shorter pattern increased dramatically. These results were interpreted as an example of the phenomenon of dissociation between tacit knowledge and knowledge.

EFFECTS OF VARIATIONS IN LOCAL REINFORCEMENT RATE ON LOCAL RESPONSE RATE IN VARIABLE INTERVAL SCHEDULES

Rats trained to lever press for sucrose were exposed to variable-interval schedules in which (i) the probability of reinforcement in each unit of time was a constant, (ii) the probability was high in the first ten seconds after reinforcement and low thereafter, (iii) the probability was low for ten seconds and high thereafter, (iv) the probability increased with time since reinforcement, or (v) the probability was initially zero and then increased with time since reinforcement. All schedules generated similar overall reinforcement rates. A peak in local response rate occurred several seconds after reinforcement under those schedules where reinforcement rate at this time was moderate or high ([i], [ii], and [iv]). Later in the inter-reinforcement interval, local response rate was roughly constant under those schedules with a constant local reinforcement rate ([i], [ii], and [iii]), but increased steadily when local reinforcement rate increased with time since reinforcement ([iv] and [v]). Postreinforcement pauses occurred on all schedules, but were much longer when local reinforcement rate was very low in the ten seconds after reinforcement ([iii]). The interresponse time distribution was highly correlated with the distribution of reinforced interresponse times, and the distribution of postreinforcement pauses was highly correlated with the distribution of reinforced postreinforcement pauses on some schedules. However, there was no direct evidence that these correlations resulted from selective reinforcement of classes of interresponse times and pauses.

Differential effects of imipramine in rats as a function of DRL schedule value

Imipramine, a tricyclic anti-depressant, has selective effects on differential-reinforcement-of-low-response-rate (DRL) schedule performance as a function of schedule value. On a DRL 9-sec schedule of water reinforcement, imipramine at doses of 2.5 to 20.0 mg/kg resulted in no significant change in the number of reinforcements or responses. A dose of 5.0 mg/kg imipramine, given to rats performing on a DRL>72-sec schedule, produced a significant increase in the number of reinforcements and a concomittant decrease in responses. This effect was associated with a shift in the inter-response time (IRT) distribution to longer IRTs. Higher doses (20.0 and 40.0 mg/kg) decreased both response rate and reinforcement rate on the DRL 72-sec schedule. These findings demonstrate the importance of schedule parameters in determining the behavioral effects of imipramine.

Effects of cinanserin and p-chlorophenylalanine and their interaction with d-amphetamine on DRL performance in rats

The effects of the serotonin antagonist cinanserin and the serotonin depletor p-chlorophenylalanine (PCPA) were compared with the effects of d-amphetamine on responding maintained by differential-reinforcement-of-low-rate schedule (DRL). d-Amphetamine (0.25–2.0 mg/kg) increased response rates and shortened interresponse times (IRTs). Cinanserin at low doses (8, 16 and 32 mg/kg) did not alter DRL responding; high doses (48 and 64 mg/kg) decreased response rates and shortened IRTs. PCPA (200 and 300 mg/kg) decreased DRL response rates and disrupted the IRT distributions for up to 72 hours post-injection, but had few effects over the subsequent 7–8 day period. d-Amphetamine given in combination with cinanserin or administered 3, 8 and 12 days post-PCPA administration resulted in decreased response rates relative to those induced by d-amphetamine alone; the d-amphetamine-induced shortening of IRTs persisted. These results suggest that cinanserin and PCPA do not exert general response-stimulant effects and that serotonergic systems are not of major functional significance in the maintenance of low rate DRL responding. These results do suggest that serotonergic systems are involved in the manifestation of the behavioral response to amphetamine, possibly as a result of a serotonergic-catecholaminergic interaction.

ONLINE: A general-purpose BASIC microcomputer program to control and record events for operant conditioning experiments

This paper describes a general-purpose on-line microcomputer program to control and record events for a variety of simple reinforcement schedules in up to six operant chambers simultaneously. Since the program is written in BASIC, it should have wide applicability regardless of the computer manufacturer. Description. ONLINE is a compiled BASIC language program designed to service from one to six operant chambers, each running under an independent simple reinforcement schedule.The programworks by sampling a parallel input port at a rate of 100 times/sec and testing the input ports' bit pattern against a stored table of bit patterns. Events are flagged when any prescheduled bit of an input port (for example, reflecting a response in an operant chamber) is on. The program then measures the event duration in .0l-sec units and increments the response counter by one. When the event ends, the program tests the interresponse time (IRT) counter and/or the response counter to determine if reinforcement delivery is scheduled. If reinforcementis scheduled, the appropriate bit on the output port is turned on for the scheduled reinforcement duration. Following either the end of each response or the end of each reinforcement, the program tests to see if the accumulated session time or reinforcement delivery count limits have been reached. If so, the session for that operant chamber is terminated by turning off the prevailing stimulus conditions bit on the parallel output port. In addition, no further events for that operant chamber are recorded. When the session criteria for all operant chambers are met, the program displays the elapsed session time, the total number of responses emitted, and the number of reinforcements delivered to each operant chamber. The operator is then given the option of storing on disk or tape the summary data, as well as the response duration and IRT distributions for each operant chamber. Control then returns to the resident disk operating system. Hardware Requirements. The system was developed on a SWTP 6800 microcomputer using ABASIC, a BASIC language compilersuppliedby Microware Systems Corporation.' The development system had 32K of RAM, with dual-floppy disks, a single 8-bit parallel input/output (I/O) port, and an interrupt timer, all supplied by SWTP. By modifying the size of the values in the dimension statement, the program can be made to occupy less memory or to accommodate a greater number of operant chambers. In addition, since all I/O occurs in subroutines, the program can easily be modified or adapted to other machine manufactures with unique I/O requirements. In addition, simple modification of the print statements following Line 9000 (see program listing in the Appendix) permits the user with no disk system to display the frequency distributions of IRT and response duration on a printing terminal or cassette tape. Availability. Requests for additional information or for a copy of the BASIC source code and the compiled machine language code on SWTP diskette should be addressed to the author in care of the Psychology Department, Fayetteville State University, Fayetteville, North Carolina 28301. (If a copy of the program on SWTP diskette is desired, please send a check, payable to the author, for $15 to cover the cost of the diskette and postage.)

Schedule-dependent tolerance to behavioral effects of Δ 9-tetrahydrocannabinol when reinforcement frequencies are matched

Squirrel monkeys pressed a lever under a multiple interresponse-time>28-sec, modified random-interval schedule which provided comparable frequencies and temporal distributions of food pellet presentation in the two components. Daily intramuscular administration of either 0.25 or 1.00 mg/kg Δ 9-tetrahydrocannabinol resulted initially in suppression and/or disruption of responding and concomitant decreases in the frequency of food presentation in both components. Responding in both components next increased, resulting in recovery of baseline frequencies of pellet delivery during the random-interval component, but continued depression during the interresponse-time schedule. The drug-induces changes in responding under the interresponse-time schedule diminished with repeated injections, whereas response rates during the random-interval schedule sometimes remained elevated. Interresponse-time distributions under the interresponse-time schedule showed that with repeated administration of the drug only those characteristics which had the greatesteffect on reinforcement frequency recovered to baseline levels. When drug injections were replaced by daily injections of the vehicle, responding was greatly disrupted only during the random-interval component. These findings are only partially consistent with other results which suggest that tolerance development to the behavioral effects of Δ 9-tetrahydrocannabinol is greatly enhanced if the drug initially produces reinforcement loss.

Effects of phencyclidine, d-amphetamine and pentobarbital on spaced responding in mice

The effects of acute IP administration of phencyclidine (PCP), d-amphetamine (AMPH) and pentobarbital (PB) were determined in 10 mice trained to lever press on a differential reinforcement of low rate 10 sec schedule of sweetened milk presentation. The effects of PCP were highly consistent, with large response rate increases (and a corresponding shift toward shorter interresponse times) at doses of 1 and 3 mg/kg. Higher doses generally decreased response rates and resulted in a bimodal interresponse time distribution. The effects of AMPH were similar to PCP but less consistent. Although some of the subjects showed substantial response rate increases at doses between 0.3 and 10 mg/kg, half of the subjects did not show increased response rates at any dose. The effects of AMPH on the interresponse time distribution were similar to PCP. The effects of PB were least like those of PCP. The effect in most subjects was to produce a dose-related decrease in response rate and a flattering of the interresponse time distribution. Occasional small response rate increases were observed with PB.

Progressive ratio and fixed ratio schedules of cocaine-maintained responding in baboons.

Responding maintained under progressive ratio (PR) and fixed ratio (FR 160) schedules of IV saline or cocaine (0.01-4.0 mg/kg) injections was studied in baboons. Each injection was followed by a time-out period which was 3-h with the PR schedule and was either 3 or 12 with the FR schedule. On the PR schedule the ratio requirement was systematically increased each day until reaching the 'breaking point' at which self-injection performance fell below a criterion level (one or zero injections per day). Overall response rates on the PR schedule increased with progressive increases in the ratio until a maximum at which an abrupt reduction in responding occurred. With the 3-h time-out the dose-breaking point function on the PR schedule was similar to the dose-response rate function on the FR schedule. These dose-effect functions were inverted U-shaped curves characterized by a graded ascending limb (0.01-0.32 mg/kg) and a downturn at the highest doses (3.0-4.0 mg/kg). On the FR schedule the downturn in the dose-response rate function was attributable to a cumulative drug effect as revealed by manipulation of time-out duration and analysis of sequential interresponse time distributions and cumulative response records. PR and FR schedules provide similar information about the relative reinforcing efficacy of different cocaine doses.

Methylphenidate and d-amphetamine: effects and interactions with alphamethyltyrosine and tetrabenazine on DRL performance in rats.

The effects of d-amphetamine and methylphenidate and their interactions with amine-depleting drugs were examined in rats trained to press a lever to obtain water reinforcement on a schedule that differentially reinforced responding at low rates (DRL). Both methylphenidate (2.5-20.0 mg/kg) and d-amphetamine (0.375-3.0 mg/kg) increased the rate of responding and decreased the frequency of reinforcement on the DRL schedule. Both drugs also shifted the interresponse time (IRT) distributions to the left such that the modal IRT occurred well below the minimum IRT required for reinforcement (d-amphetamine was abut eight times more potent than methylphenidate for each of these effects). The effects of both d-amphetamine and methylphenidate on DRL performance were attenuated by administration of alphamethyltyrosine (AMT) (150 mg/kg) and both drugs attenuated the response rate-suppressing effects of tetrabenazine (TBZ) (4.0 mg/kg). The similarity of the drug interactions between methylphenidate or amphetamine and AMT or TBZ suggest that the doses of methylphenidate and d-amphetamine examined act on similar catecholaminergic pools with the central nervous system to influence DRL performance.

THE EFFECT OF FOREPERIOD DURATION ON REACTION TIME AND ITS RELATION TO INTERVAL SCHEDULES OF REINFORCEMENT

Two groups of pigeons were exposed to a simple reaction-time procedure in which mean foreperiod duration was 5, 10, or 20 seconds. For one group, the foreperiods had an arithmetic, or rectangular, distribution; for the second group, they had a constant-probability, or Bernoulli, distribution. Under both distributions, mean response latency was an increasing, negatively accelerated function of mean foreperiod duration. On a given trial, response latency was a function of its associated foreperiod duration: latency was a decreasing function of foreperiod duration in the arithmetic distribution, and an increasing function of foreperiod duration in the constant-probability distribution. Examination of the distribution of latencies revealed a harmonic structure reminiscent of distributions of interresponse times under variable-interval schedules of reinforcement. Taken together, the results confirm and extend previous findings with human subjects, and also suggest numerous similarities to behavior maintained by variable-interval schedules.

Psychotropic drugs and sidman avoidance in rats: IRT distribution changes

The effects of d-amphetamine, caffeine, chlorpromazine, diazepam and pentobarbital on Sidman avoidance responding (R-S interval, 30 sec; S-S interval, 3 sec) in rats, especially on the interresponse time (IRT) distribution, were studied. d-Amphetamine and caffeine increased the total number of responses. Short IRTs were increased, while longer ones were decreased. Chlorpromazine, diazepam and pentobarbital all increased the number of shocks delivered. After chlorpromazine, no marked change was observed in the total number of responses. However, response bursts and escape responses increased, while IRTs between 3 and 30 sec decreased. After diazepam and pentobarbital, the burst response scarcely increased, and the IRTs in the 3–15 sec range decreased, while the IRTs longer than 33 sec increased. These changes were more marked after diazepam than after pentobarbital. Total number of responses was decreased by both drugs. The present results suggest that in utilizing the Sidman avoidance procedure for psychotropic drug assessment, changes in the IRT distribution give a more precise profile of the drug than is afforded by the total number of responses and shocks delivered.

Effects of lead on temporally-spaced responding in rats.

The effects of lead acetate and aging on temporally-spaced responding (differential reinforcement of low rate or DRL-20 seconds) were studied. Three groups of animals were considered along with their respective controls. Neonate-treated Long-Evans rats were orally intubated with 200 mg/kg lead acetate from the third to 30th day after birth. Some of these animals were tested at 3 months (adult group) and some at 21 months (geriatric group) of age. A continuously treated group was exposed to 250 ppm lead in utero and throughout their life after birth and was treated at 8 months of age. Lead-treated animals exhibited a more variable response to d-amphetamine and a more pronounced number of IRTs in the first class interval. Aging shifted the pentobarbital dose-response curve to the left in both control and lead-treated animals and flattened interresponse time (IRT) distributions.

The effect of cue-fading on the DRL performance of septal and normal rats

The effect of a cue-light fading procedure on the subsequent noncued performance under a differential-reinforcement-of-low-rate schedule (DRL) of food reinforcement was determined for rats with septal lesions and normal rats. Following initial DRL-20 sec training, all animals were trained with a cued DRL schedule in which a light signaled the end of the required delay and the availability of reinforcement. Subsequently, for one-half of the animals, the cue light was abruptly discontinued; for the remainder of the subjects, the cue was gradually faded out over succeeding sessions. Septal animals, which had the cue gradually faded, were more efficient by the end of training than septal animals which had the light abruptly discontinued. Moreover, the former did not differ from normal controls. For septal animals in the Fade group, the relative frequency distributions of interresponse times (IRTs) were bimodal, a characteristic of normal animals; septal animals which had the cue abruptly terminated, displayed the unimodal distribution of IRTs which is a characteristic of septal animals on the DRL schedule. In summary, the cue-fading procedure completely eliminated the major differences in behavior between normal and septal rats typically observed on a DRL schedule of food reinforcement.

A MOLECULAR ANALYSIS OF MULTIPLE SCHEDULE INTERACTIONS: NEGATIVE CONTRAST1

The present experiments investigated the relationship between changes in the relative reinforced interresponse-time distributions and the occurrence of positive and negative contrast in multiple variable-interval-variable-interval and multiple variable-interval-extinction schedules of reinforcement. Experiment I demonstrated that changes in the interresponse-time distributions were consistently correlated with response-rate changes referred to as positive and negative contrast. Corresponding changes in the reinforced interresponse-time distributions suggested that negative contrast resulted as an inductive effect of selectively reinforcing long interresponse times in the altered component at the moment the baseline schedule was reintroduced. Experiment II demonstrated that the magnitude of the negative-contrast effect could be significantly decreased if the altered component schedule was modified in order to prevent the reinforcement of these interresponse times during the first few sessions of baseline recovery. The results supported a proposal that interresponse time-reinforcer relations may act as amplifiers or attenuators of negative contrast.

SOME IMPLICATIONS OF A RELATIONAL PRINCIPLE OF REINFORCEMENT1

A formal statement of a relational principle of reinforcement is developed that makes contact with analyses of choice, interresponse-time distributions, and stimulus control. Some implications for current theoretical and empirical work in the various areas are examined.

The effects of brief exposures to carbon monoxide on temporally differentiated responding

Four rats were trained on a differential-reinforcement-of-low-rate schedule under which only responses separated by intervals of 21 seconds produced food. Ninety-minute exposures to 100, 250, 500, 600, 750, and 1000 ppm carbon monoxide were given. Overall response rates were lower than rates in control sessions for all subjects at 750 ppm and higher concentrations. Measures of temporal discrimination (distributions of interresponse times), however, were not disrupted. The primary effect of the higher concentrations of carbon monoxide was to produce extended pausing or complete cessation of responding at some point in the session. Until pausing occurred, however, the control rate and patterning of responding obtained. The results are consistent with the growing body of evidence that carbon monoxide has a general rate-decreasing effect but no specific effect on measures of temporal discrimination.

LOCAL PATTERNS OF RESPONDING MAINTAINED BY CONCURRENT AND MULTIPLE SCHEDULES1

Local patterns of responding were studied when pigeons pecked for food in concurrent variable-interval schedules (Experiment I) and in multiple variable-interval schedules (Experiment II). In Experiment I, similarities in the distribution of interresponse times on the two keys provided further evidence that responding on concurrent schedules is determined more by allocation of time than by changes in local pattern of responding. Relative responding in local intervals since a preceding reinforcement showed consistent deviations from matching between relative responding and relative reinforcement in various postreinforcement intervals. Response rates in local intervals since a preceding changeover showed that rate of responding is not the same on both keys in all postchangeover intervals. The relative amount of time consumed by interchangeover times of a given duration approximately matched relative frequency of reinforced interchangeover times of that duration. However, computer simulation showed that this matching was probably a necessary artifact of concurrent schedules. In Experiment II, when component durations were 180 sec, the relationship between distribution of interresponse times and rate of reinforcement in the component showed that responding was determined by local pattern of responding in the components. Since responding on concurrent schedules appears to be determined by time allocation, this result would establish a behavioral difference between multiple and concurrent schedules. However, when component durations were 5 sec, local pattern of responding in a component (defined by interresponse times) was less important in determining responding than was amount of time spent responding in a component (defined by latencies). In fact, with 5-sec component durations, the relative amount of time spent responding in a component approximately matched relative frequency of reinforcement in the component. Thus, as component durations in multiple schedules decrease, multiple schedules become more like concurrent schedules, in the sense that responding is affected by allocation of time rather than by local pattern of responding.

BEHAVIORAL INTERACTIONS IN MULTIPLE VARIABLE‐INTERVAL SCHEDULES1

In Experiment I, two groups of four pigeons each were exposed to multiple schedules in which one component was always a variable-interval schedule with a mean interreinforcement interval of 30 or 180 seconds. The other component was either an equal variable-interval schedule or extinction. Response rates in the unchanged component always increased when reinforcement was no longer scheduled in the changed component, and decreased in seven of eight cases when the variable-interval schedule was re-introduced. The per cent rate change in the unchanged component was inversely related to the frequency of reinforcement and to the ongoing response rate in the unchanged component. Rate changes in the unchanged component were not consistently correlated with changes in any single feature of the relative-frequency interresponse-time distributions. In Experiment II, the same pigeons were exposed to variable-interval schedules and multiple variable-interval variable-interval schedules with equal mean interreinforcement intervals. Response rates were similar under both conditions.

CHOICE BETWEEN RESPONSE RATES1

Three pigeons were required to peck a single key at a higher and a lower rate, corresponding to two classes of shorter and longer concurrently reinforced interresponse times. Food reinforcers arranged by a single variable-interval schedule were randomly allocated to the two reinforced interresponse times. The absolute durations of reinforced interresponse times were varied while the total reinforcements per hour was held constant and the relative duration, i.e., the relative reciprocal, of the shorter reinforcer class was held constant at 0.70. Preference for the higher rate of responding, as measured by the relative frequency of responses terminating interresponse times in the shorter reinforced class, depended on the absolute reinforced response rates. Preference for the higher reinforced rate increased from a level of near-indifference (0.50) at high reinforced response rates, through the matching level (0.70) at intermediate reinforced response rates, to a virtually exclusive preference (>0.90) at low reinforced response rates. These results resemble corresponding preference functions obtained with two-key concurrent-chains schedules and thereby provide another sense in which it may be said that interresponse-time distributions from interval schedules estimate preference functions for the component response rates corresponding to different classes of reinforced interresponse times.