The role of verbal behavior in human learning: infant performance on fixed-interval schedules

The performances of two infants less than one year old were investigated on fixed-interval schedules. When the infants touched a cylinder either music or food was presented according to fixed-interval schedules ranging in value from 10 to 50 seconds. With respect to two principal criteria, namely, pattern of responding and sensitivity to the schedule parameter, the subjects' behavior closely resembled that of animals but differed markedly from that of older children and adults. Negatively accelerated responding in the course of the fixed interval in the early sessions gave way to a scalloped pattern, consisting of a pause after reinforcement followed by an accelerated response rate. This scalloped pattern was the final form of responding on all schedule values. Analysis of data after performance had stabilized showed that postreinforcement pause was a negatively accelerated increasing function, and running rate (calculated after excluding the postreinforcement pause) was a declining function, of schedule value. On each schedule, the durations of mean successive interresponse times declined in the course of the fixed interval and were directly related to schedule value. The results supported Lowe's (1979) suggestion that verbal behavior may be responsible for major differences in the schedule performance of older humans and animals.     

Changing the response unit from a single peck to a fixed number of pecks in fixed-interval schedules

Each of three pigeons was studied first under a standard fixed-interval schedule. With the fixed interval held constant, the schedule was changed to a second-order schedule in which the response unit was the behavior on a small fixed-ratio schedule (first a fixed-ratio 10 and then a fixed-ratio 20 schedule). That is, every completion of the fixed-ratio schedule produced a 0.7-sec darkening of the key and reset the response count to zero for the next ratio. The first fixed-ratio completed after the fixed-interval schedule elapsed produced the 0.7-sec blackout followed immediately by food. These manipulations were carried out under two different fixed-interval durations for each bird ranging from 3 min to 12 min. The standard fixed-interval schedules produced the typical pause after reinforcement followed by responding at a moderate rate until the next reinforcement. The second-order schedules also engendered a pause after reinforcement, but responding occurred in bursts separated by brief pauses after each blackout. For a particular fixed-interval duration, post-reinforcement pauses increased slightly as the number of pecks in the response unit increased despite large differences in the rate and pattern of key pecking. Post-reinforcement pause increased with the fixed-interval duration under all response units. These data confirm that the allocation of time between pausing and responding is relatively independent of the rate and topography of responding after the pause.     

Studies on responding under fixed-interval schedules of reinforcement: II. The scalloped pattern of the cumulative record

Responding under fixed-interval schedules usually generates either scalloped or break-and-run cumulative records. Earlier, it was generally accepted that the characteristic pattern was the scallop, but in recent years there has been an increasing emphasis on the break-and-run pattern. The break-and-run pattern has been shown quantitatively to provide a good fit of certain fixed-interval patterns. In the present work, responding during fixed-interval 1000-second components of a multiple fixed-interval 1000-second fixed-ratio 50 responses schedule was examined in two rhesus monkeys. Even after responding had started in an interval, there was a high tendency for responding to accelerate over subsequent 100-second segments of the interval. In segments with responding, the rate increased from one segment to the next in 303 of 389 segments in one monkey and in 310 of 419 segments in the other. The size of the increase was substantial, the rate in the fifth segment after responding started being an average of 4.5 times higher than the rate in the first segment after responding started. Hence, the usual pattern of responding in individual intervals was of sustained and substantial acceleration, vindicating numerically the conclusion derived from inspection of the scalloped patterns of the cumulative records.     

Handwriting as an operant

An apparatus was designed to monitor handwriting behavior. Two subjects were studied under various schedules of monetary reinforcement for handwriting. The different schedules engendered and maintained distinctive response patterns but the rates of sustained responding did not vary across schedules. The development of fixed-interval performance following continuous reinforcement resembled the same transition in lower animals. In one subject, availability of reading material interacted with the schedule to determine response pattern. It was suggested that handwriting may be a more appropriate response for the experimental analysis of human behavior than the more frequently used button-pushing or lever-pulling responses.     

Studies on responding under fixed-interval schedules of reinforcement: the effects on the pattern of responding of changes in requirements at reinforcement

In pigeons responding under a 180-sec fixed-interval schedule of reinforcement, the frequency distribution of the duration of the final interresponse time before the reinforcer was compared with the distribution of the preceding two interresponse times. The results confirmed qualitatively and quantitatively the expected preferential reinforcement of longer interreinforcement times under fixed-interval reinforcement. Requirements at reinforcement were then changed to eliminate the preferential reinforcement of longer interresponse times. Local patterns and mean rate of responding could change, without the characteristic fixed-interval pattern of increasing responding through the interval (scalloping) being much affected. It is concluded that this characteristic pattern of fixed-interval responding does not depend crucially on effects of the reinforcer at the moment of reinforcement, but rather to effects extending over much longer periods of time than just the last interresponse time.     

A half century of scalloping in the work habits of the United States Congress

It has been suggested that the work environment of the United States Congress bears similarity to a fixed-interval reinforcement schedule. Consistent with this notion, Weisberg and Waldrop (1972) described a positively accelerating pattern in annual congressional bill production (selected years from 1947 to 1968) that is reminiscent of the scalloped response pattern often attributed to fixed-interval schedules, but their analysis is now dated and does not bear on the functional relations that might yield scalloping. The present study described annual congressional bill production over a period of 52 years and empirically evaluated predictions derived from four hypotheses about the mechanisms that underlie scalloping. Scalloping occurred reliably in every year. The data supported several predictions about congressional productivity based on fixed-interval schedule performance, but did not consistently support any of three alternative accounts. These findings argue for the external validity of schedule-controlled operant behavior as measured in the laboratory. The present analysis also illustrates a largely overlooked role for applied behavior analysis: that of shedding light on the functional properties of behavior in uncontrolled settings of considerable interest to the public.     

Second-order schedules and the problem of conditioned reinforcement

Thirteen pigeons were exposed to a variety of second-order schedules in which responding under a component schedule was reinforced according to a schedule of reinforcement. Under different conditions, completion of each component resulted in either (1) the brief presentation of a stimulus also present during reinforcement (pairing operation), (2) the brief presentation of a stimulus not present during reinforcement (nonpairing operation), or (3) no brief stimulus presentation (tandem). Brief-stimulus presentations engendered a pattern of responding within components similar to that engendered by food. Patterning was observed when fixed-interval and fixed-ratio components were maintained under fixed- and variable-ratio and fixed- and variable-interval schedules. There were no apparent differences in performance under pairing and nonpairing conditions in any study. The properties of the stimuli presented in brief-stimulus operations produced different effects on response patterning. In one study, similar effects on performance were found whether brief-stimulus presentations were response-produced or delivered independently of responding. Response patterning did not occur when the component schedule under which a nonpaired stimulus was produced occurred independently of the food schedule. The results suggest a reevaluation of the role of conditioned reinforcement in second-order schedule performance. The similarity of behavior under pairing and nonpairing operations is consistent with two hypotheses: (1) the major effect is due to the discriminative properties of the brief stimulus; (2) the scheduling operation under which the paired or nonpaired stimulus is presented can establish it as a reinforcer.     

Schedule control of the vocal behavior of Cebus monkeys

The vocal behavior of three Cebus monkeys was maintained by fixed-ratio schedules of response dependent reinforcement at values between fixed-ratio 1 and fixed-ratio 15. In one monkey that was exposed to variable-interval, fixed-interval, and conjunctive fixed-ratio fixed-interval schedules of reinforcement, vocal responding occurred at a low rate, but schedule-appropriate patterns were maintained. The rates and patterns of responding engendered indicated that the vocal operant can be brought under schedule control in the monkey by the use of response-dependent reinforcement.     

On the form of the relation between response rates in a multiple schedule

Three pigeons received training on multiple variable-interval schedules with brief alternating components, concurrently with a fixed-interval schedule of food reinforcement on a second key. Fixed-interval performance exhibited typical increases in rate within the interval, and was independent of multiple-schedule responding. Responding on the multiple-schedule key decreased as a function of proximity to reinforcement on the fixed-interval key. The overall relative rate of responding in one component of the multiple schedule roughly matched the overall relative rate of reinforcement. Within the fixed interval, response rate during one multiple-schedule component was a monotonic, negatively accelerated function of response rate during the other component. To a first approximation, the data were described by a power function, where the exponent depended on the relative rate of reinforcement obtained in the two components. The relative rate of responding in one component of the multiple schedule increased as a function of proximity to fixed-interval reinforcement, and often exceeded the overall obtained relative rate of reinforcement. The form of the function relating response rates is discussed in relation to findings on rate-dependent effects of drugs, chaining, and the relation between response rate and reinforcement rate in single-schedule conditions.     

Schedules using noxious stimuli. IV: An interlocking shock-postponement schedule in the squirrel monkey

Responding was studied under various schedules of electric shock postponement and presentatation in the squirrel monkey. Under an interlocking shock-postponement schedule, successive responses decreased the time by which a response postponed the next scheduled shock until a shock immediately followed the nth response. Some parameters of this schedule, which can be formally related to fixed-interval schedules, engendered a pattern of positively accelerated responding between shocks. This pattern did not occur under comparable parameter values of an alternative fixed-ratio, avoidance schedule under which each response postponed shock by a fixed duration and every nth response produced shock. Subsequently, performances were studied under schedules of shock presentation. Responding was never maintained under fixed-ratio schedules of shock presentation, but was maintained with a pattern of positive acceleration under an alternative fixed-ratio, fixed-interval schedule and under a fixed-interval schedule.     

Effects of concurrent response-independent reinforcement on fixed-interval schedule performance

In three experiments, behavior maintained by fixed-interval schedules changed when response-independent reinforcement was delivered concurrently according to fixed- or variable-time schedules. In Experiment I, a pattern of positively accelerated responding during fixed interval was changed to a linear pattern when response-independent reinforcement occurred under a variable-time schedule. Overall response rates (total responses/total time) decreased as the frequency of response-independent reinforcement increased. Experiment II showed that the response-rate changes in the first experiment were controlled by the response-reinforcer relation, but the changes in patterns of responding were similar whether concurrently available reinforcement at varying times was response-dependent or response-independent. In the final experiment, the addition of response-independent reinforcement at fixed times to a fixed-interval schedule resulted in changes in both local and overall response rates and in the occurrence of positively accelerated responding between reinforcements. These results suggest that the temporal distribution of reinforcers determines response patterns and that both the response-reinforcement dependency and the schedule of reinforcement determine overall response rates during concurrently scheduled response-dependent and response-independent reinforcement.     

Intractable properties of responding under a fixed-interval schedule

The behavior engendered by the fixed-interval schedule is characterized by its variability within and across intervals. The present experiment was designed to assess further the magnitude of interval-to-interval dynamics and to explore conditions which might enhance control by response number for subsequent output. Pigeons were exposed to three experimental manipulations after responding had stabilized under a fixed-interval five-minute schedule. First, a discrete five-stimulus counter was added so that the key color changed after a fixed number of responses. Then additional grain presentations were made at the end of the interval so that high response output was differentially reinforced in the presence of the counter stimuli. Finally, the counter stimuli were presented as an irregular clock (i.e., independently of responding), but the durations were yoked to performance under the counter condition. The data show that response number can exert influence from one interval to the next, but this source of control is weak and not influenced by the experimental manipulations. Results from the clock arrangement indicate that behavior is controlled largely by the stimulus conditions prevailing at the time of interval onset.     

Conditioned suppression or facilitation as a function of the behavioral baseline

Rats were exposed to a multiple schedule of reinforcement. During one component, a bar-press was followed by reinforcement only if it occurred between 15 and 20 sec after the previous response. This differential-reinforcement-of-low-rate (DRL) schedule produced a typical slow rate of responding. During the other component, reinforcement followed the first response to be emitted during limited periods of time which occurred at fixed intervals. These fixed-interval schedules with a limited hold produced higher response rates, described as `interval' or `ratio-like' behavior. Responding during the DRL component increased in frequency during a tone which ended with an unavoidable shock of low intensity, but decreased during the tone when the shock intensity was raised. The `interval' and `ratio-like' responding decreased in frequency during the tone at all shock intensities. Initial acceleration of the DRL responding appeared to be due to adventitious punishment of collateral behavior which was observed between the bar-presses. The more severe conditioned suppression during the fixed-interval components might be the result of the lower probability of reinforcement after any single response.     

Differential effects of cocaine and pentobarbital on fixed-interval and random-interval performance

Reports have indicated that the behavioral effects of a drug can be related to the nondrug control rate of behavior in the absence of the drug. To investigate the purported relationship between control rate and drug rate, squirrel monkeys were trained under a fixed-interval 300-s schedule of stimulus-shock termination, a procedure that engendered a wide range of response rates. A light illuminated the experimental chamber during the fixed interval, and the first lever press after 300 s had elapsed terminated the light for 30 s and precluded an electrical stimulus to the tail. Following acute intramuscular administration of cocaine (0.03-0.56 mg/kg), overall rate increased and different control rates of responding, during different parts of the fixed interval, converged toward a common rate. Subsequently, the schedule was changed to a multiple fixed-interval 300-s random-interval 300-s schedule; performance during the random-interval component was characterized by steady responding at a uniformly high rate. Analysis of fixed-interval and random-interval performances following acute cocaine administration revealed convergence of response rates toward a common, uniform rate. Pentobarbital (0.3-10.0 mg/kg) only decreased overall rate, and different control rates of responding during the fixed interval did not converge toward a common rate. The results indicate that this type of analysis can be useful in comparing pharmacological agents from different classes and that the rate at which responding becomes uniform can provide a quantitative behavioral end point for characterizing drug effects on behavior.     

Responding maintained under fixed-interval and fixed-time schedules of electric shock presentation

Following initial histories under a schedule of electric shock postponement, lever pressing in squirrel monkeys was maintained under fixed-interval and fixed-time schedules of electric shock presentation. No difference in either rate or pattern of responding was obtained when these schedules were presented as components of a multiple schedule. When they were presented singly for long periods of time, the fixed-interval schedule consistently maintained a higher response rate than the fixed-time schedule. The pattern of responding under both schedules was similar, typically consisting of a pause at the beginning of each interval followed by either a steady or a positively accelerating rate of responding. The results suggest that the response-shock dependency is of critical importance in the maintenance of high rates of responding under schedules of electric shock presentation, and support the general view that such responding may be conceptualized as operant behavior under control of many of the same variables that control responding under comparable schedules of food or water reinforcement.     

A quantitative analysis of the responding maintained by interval schedules of reinforcement

Interval schedules of reinforcement maintained pigeons' key-pecking in six experiments. Each schedule was specified in terms of mean interval, which determined the maximum rate of reinforcement possible, and distribution of intervals, which ranged from many-valued (variable-interval) to single-valued (fixed-interval). In Exp. 1, the relative durations of a sequence of intervals from an arithmetic progression were held constant while the mean interval was varied. Rate of responding was a monotonically increasing, negatively accelerated function of rate of reinforcement over a range from 8.4 to 300 reinforcements per hour. The rate of responding also increased as time passed within the individual intervals of a given schedule. In Exp. 2 and 3, several variable-interval schedules made up of different sequences of intervals were examined. In each schedule, the rate of responding at a particular time within an interval was shown to depend at least in part on the local rate of reinforcement at that time, derived from a measure of the probability of reinforcement at that time and the proximity of potential reinforcements at other times. The functional relationship between rate of responding and rate of reinforcement at different times within the intervals of a single schedule was similar to that obtained across different schedules in Exp. 1. Experiments 4, 5, and 6 examined fixed-interval and two-valued (mixed fixed-interval fixed-interval) schedules, and demonstrated that reinforcement at one time in an interval had substantial effects on responding maintained at other times. It was concluded that the rate of responding maintained by a given interval schedule depends not on the overall rate of reinforcement provided but rather on the summation of different local effects of reinforcement at different times within intervals.     

A comparison of responding maintained under second-order schedules of intramuscular cocaine injection or food presentation in squirrel monkeys.

Key pressing by squirrel monkeys was maintained under second-order schedules of either intramuscular cocaine injection or food presentation. Under one schedule, each completion of a 10-response fixed-ratio unit produced a brief visual stimulus; the first fixed-ratio unit completed after 30 minutes elapsed produced the stimulus paired with either cocaine injection or food presentation. Generally, short pauses followed by high rates of responding were maintained within the fixed-ratio units, and responding was positively accelerated over the 30-minute interval. Under another schedule, each completion of a 3-minute fixed-interval unit produced the brief stimulus; completion of the 10th fixed-interval unit produced the stimulus paired with either cocaine injection or food presentation. Generally, short pauses followed by high rates of responding were maintained within the fixed-ratio units, and responding was positively accelerated over the 30-minute interval. Under another schedule, each completion of a 3-minute fixed-interval unit produced the brief stimulus; completion of the 10th fixed-interval unit produced the stimulus paired with either cocaine injection or food presentation. Rates of responding increased within the fixed-interval units, and to a greater extent over the entire 10 fixed-interval units. Patterns of responding depended more on the schedule of reinforcement than on whether cocaine or food maintained responding. Omitting the brief stimuli following all but the last fixed-ratio or fixed-interval units decreased average rates and altered the patterns of responding. Substituting a visual stimulus that was never paired with cocaine or food following all but the last fixed-ratio or fixed-interval units decreased response rates to a lesser extent and did not substantially alter patterns of responding. When the duration of the paired stimulus was varied from .3 to 30.0 seconds, the highest response rates occurred at intermediate durations (1.0 to 10.0 seconds). The manner in which the stimulus changes affected performances depended more on the schedule of reinforcement than on whether cocaine injection or food presentation maintained responding.     

An inverse relationship between baseline fixed-interval response rate and the effects of a tandem response requirement.

Previous experiments examining the effects of adding a tandem fixed-ratio response requirement on fixed-interval schedule performance have reported inconsistent results. One variable that may account for such inconsistencies is the baseline response rate in the fixed-interval condition. This possibility was investigated in the present study. Rats were given histories with either interresponse times greater than 11 s or fixed-ratio 40 schedules of reinforcement, which engendered either relatively low or high rates of responding, respectively, in the subsequent fixed-interval condition. A tandem ratio response requirement (fixed-ratio 9) was then introduced. The effects of adding this tandem response requirement were inversely related to the baseline fixed-interval response rates; low rates of responding in the fixed-interval condition were markedly increased, whereas high rates of responding were relatively unaffected. This inverse relationship appears to be similar to the rate-dependent relations observed in behavioral pharmacology. These results may provide an explanation for the inconsistent findings reported in previous studies on tandem fixed-interval fixed-ratio schedules and suggest that principles of behavioral pharmacology research may be applicable to the study of the effects of nonpharmacological variables on schedule-controlled behavior.     

Concurrent fixed-interval variable-ratio schedules and the matching relation

Five rats responded under concurrent fixed-interval variable-ratio schedules of food reinforcement. Fixed-interval values ranged from 50-seconds to 300-seconds and variable-ratio values ranged from 30 to 360; a five-second changeover delay was in effect throughout the experiment. The relations between reinforcement ratios obtained from the two schedules and the ratios of responses and time spent on the schedules were described by Baum's (1974) generalized matching equation. All subjects undermatched both response and time ratios to reinforcement ratios, and all subjects displayed systematic bias in favor of the variable-ratio schedules. Response ratios undermatched reinforcement ratios less than did time ratios, but response ratios produced greater bias than did time ratios for every subject and for the group as a whole. Local rates of responding were generally higher on the variable-ratio than on the fixed-interval schedules. When responding was maintained by both schedules, a period of no responding on either schedule immediately after fixed-interval reinforcement typically was followed by high-rate responding on the variable-ratio schedule. At short fixed-interval values, when a changeover to the fixed-interval schedule was made, responding usually continued until fixed-interval reinforcement was obtained; at longer values, a changeover back to the variable-ratio schedule usually occurred when fixed-interval reinforcement was not forthcoming within a few seconds, and responding then alternated between the two schedules every few seconds until fixed-interval reinforcement finally was obtained.     

The response-reinforcement dependency in fixed-interval schedules of reinforcement

Pigeons were exposed to four different schedules of food reinforcement that arranged a fixed minimum time interval between reinforcements (60 sec or 300 sec). The first was a standard fixed-interval schedule. The second was a schedule in which food was presented automatically at the end of the fixed time interval as long as a response had occurred earlier. The third and fourth schedules were identical to the first two except that the first response after reinforcement changed the color on the key. When the schedule required a peck after the interval elapsed, the response pattern consisted of a pause after reinforcement followed by responding at a high rate until reinforcement. When a response was not required after the termination of the interval, the pattern consisted of a pause after reinforcement, followed by responses and then by a subsequent pause until reinforcement. Having the first response after reinforcement change the color on the key had little effect on performance. Post-reinforcement pause duration varied with the minimum interreinforcement interval but was unaffected by whether or not a response was required after the interval elapsed.