Control rate of response or reinforcement and amphetamine's effect on behavior.

The roles of control response rate and reinforcement frequency in producing amphetamine's effect on operant behavior were evaluated independently in rats. Two multiple schedules were arranged in which one variable, either response rate or reinforcement frequency, was held constant and the other variable manipulated. A multiple differential-reinforcement-of-low-rate seven-second yoked variable-interval schedule was used to equate reinforcement frequencies at different control response rates between multiple-schedule components. Amphetamine increased responding under the variable-interval component. In contrast, amphetamine decreased responding equivalently between components of a multiple random-ratio schedule that produced similar control response rates at different reinforcement frequencies. The results provide experimental support to the rate-dependency principle that control rate of responding is an important determinant of amphetamine's effect on operant behavior.     

Reinforcement of inhibition

A differential-reinforcement-of-other-behavior (DRO) schedule with trials and delayed reinforcement was investigated. Periodically a wheel was briefly available to rats, followed six seconds later by brief availability of a bar. Variable-ratio food reinforcement of wheel turns was adjusted to give 95% turns. After variable-ratio-five reinforcement of bar presses produced 100% pressing, then separate ratio schedules were used for presses following turns (turn presses) and presses following nonturns (nonturn presses). Increasing nonturn-press reinforcements decreased turns, even though total reinforcements increased. Reversal by decreasing nonturn-press reinforcements raised turns, though with hysteresis. Thus food reinforcement increased nonturns even though delayed six to ten seconds after nonturns, a delay that greatly reduces response reinforcement. Those and other results indicate that the turn decrease was not due to reinforcement of competing responses. Evidence against other alternatives, and the reduction of responding by increased reinforcement, indicate that the term inhibition is appropriate for the phenomenon reinforced. Response-specific inhibition appears appropriate for this particular kind, since its effects are more specific to particular responses than Pavlovian conditioned-inhibition. Response-specific inhibition seems best considered a behavioral output comparable to responses (e.g., both reinforcible) but with important properties different from responses (e.g., different reinforcement-delay gradients).     

Second-order schedules: discrimination of components

Pigeons were exposed to a series of second-order schedules in which the completion of a fixed number of fixed-interval components produced food. In Experiment 1, brief (2 sec) stimulus presentations occurred as each fixed-interval component was completed. During the brief-stimulus presentation terminating the last fixed-interval component, a response was required on a second key, the brief-stimulus key, to produce food. Responses on the brief-stimulus key before the last brief-stimulus presentation had no scheduled consequences, but served as a measure of the extent to which the final component was discriminated from preceding components. Whether there were one, two, four, or eight fixed-interval components, responses on the brief-stimulus key occurred during virtually every brief-stimulus presentation. In Experiment 2, an attempt was made to punish unnecessary responses on the brief-stimulus key, i.e., responses on the brief-stimulus key that occurred before the last component. None of the pigeons learned to withhold these responses, even though they produced a 15-sec timeout and loss of primary reinforcement. In Experiment 3, different key colors were associated with each component of a second-order schedule (a chain schedule). In contrast to Experiment 1, brief-stimulus key responses were confined to the last component. It was concluded that pigeons do not discriminate well between components of second-order schedules unless a unique exteroceptive cue is provided for each component. The relative discriminability of the components may account for the observed differences in initial-component response rates between comparable brief-stimulus, tandem, and chain schedules.     

Responding under positive and negative response contingencies in pigeons and crows

Four crows were trained to key peck for food. Then, they were exposed to a positive response contingency that required them to peck the key when it was illuminated briefly (the trial) in order to receive food. This procedure resulted in consistent within-trial pecking. When the contingency changed so that food was presented at the end of a trial when no response occurred, but the trial terminated immediately and food was omitted when a response occurred (negative response contingency), responding decreased markedly. Eight pigeons were studied under the same change in contingencies. These birds varied in their response histories from naive to having several years' experience. The previously naive pigeons also showed rapid declines in responding under the negative contingency; the responding of the birds with extended training histories declined much more slowly. Eventually, however, six of the eight pigeons showed little or no responding under the negative contingency, while they responded consistently when re-exposed to the positive contingency. These findings question the power and the generality of the negative automaintenance phenomenon.     

Aftereffects of reinforcement on variable-ratio schedules

On each of variable-ratio 10, 40, and 80 schedules of reinforcement, when rats' lever-pressing rates were stable, the concentration of a liquid reinforcer was varied within sessions. The duration of the postreinforcement pause was an increasing function of the reinforcer concentration, this effect being more marked the higher the schedule parameter. The running rate, calculated by excluding the postreinforcement pause, was unaffected by concentration. The duration of the postreinforcement pause increased with the schedule parameter, but the proportion of the interreinforcement interval taken up by the pause decreased. Consequently, the overall response rate was an increasing function of the schedule parameter; i.e., it was inversely related to reinforcement frequency, contrary to the law of effect. The running rate, however, decreased with the reinforcement frequency, in accord with the law of effect. When 50% of reinforcements were randomly omitted, the postomission pause was shorter than the postreinforcement pause, but the running rate of responses was not affected.     

The effects of unsignalled delayed reinforcement

Pigeons' pecks were reinforced according to a variable-interval schedule. A delay-of-reinforcement procedure was then added to the schedule, or a yoked-control procedure was arranged where the reinforcers occurred independently of responding according to the same variable-interval schedule. During the delay-of-reinforcement procedure, the first peck after a reinforcer was scheduled began a delay timer and the reinforcer was delivered at the end of the interval. No stimulus change signalled the delay interval and responses could occur during it, so that the obtained delays were often shorter than those scheduled. Responding under this procedure was highly variable but, in general, behavior was substantially reduced even with the shortest delay used, 3 sec. In addition, the rates maintained by delayed reinforcement were only slightly greater than those maintained by the yoked-control procedure, suggesting that adventitious pairings of response and reinforcer were responsible for some of the maintenance of behavior that did occur. The results challenge recent conceptions of reinforcement as involving response-reinforcer correlations and re-emphasize the role of temporal proximity between response and reinforcer.     

Reinforcement rate and interresponse time differentiation

Reinforcement rate and differential reinforcement of IRTs were independently manipulated to assess their relative contribution to the control of interresponse times (IRTs). Modified percentile reinforcement schedules (Platt, 1973) allowed control of reinforcement rate while longest or shortest IRTs were selectively reinforced. In the absence of differential IRT reinforcement, mean IRT decreased with increasing reinforcement rate. Compared to this small effect of reinforcement rate, reinforcement of long IRTs produced large changes in mean IRT at constant reinforcement rates. No interaction of reinforcement rate and IRT reinforcement was detected. The demonstration of large IRT changes in the absence of reinforcement-rate changes indicates the precedence of IRT reinforcement over molar reinforcement-rate correlations in the determination of IRTs in these procedures.     

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.     

Process-specific slowing with advancing age: evidence derived from the analysis of sequential effects

In the current study we examined the generalized slowing hypothesis on the mechanisms underlying sequential effects in serial two-choice reaction time tasks. For young adults, sequential effects of conditions with a high and a low stimulus presentation rate respectively pointed to an automatic and an expectancy mechanism. Older adults' low presentation rate data corroborated the general slowing hypothesis for expectancy, whereas the high presentation rate results did not. The observation of a differential influence of age on the automatic and the expectancy mechanism poses a problem for notions assuming that higher level processes are more vulnerable to advancing age than lower level processes.     

Competition between noncontingent and contingent reinforcement schedules during response acquisition

We examined the extent to which noncontingent reinforcement (NCR), when used as treatment to reduce problem behavior, might interfere with differential reinforcement contingencies designed to strengthen alternative behavior. After conducting a functional analysis to identify the reinforcers maintaining 2 participants' self-injurious behavior (SIB), we delivered those reinforcers under dense NCR schedules. We delivered the same reinforcers concurrently under differential-reinforcement-of-alternative-behavior (DRA) contingencies in an attempt to strengthen replacement behaviors (mands). Results showed that the NCR plus DRA intervention was associated with a decrease in SIB but little or no increase in appropriate mands. In a subsequent phase, when the NCR schedule was thinned while the DRA schedule remained unchanged, SIB remained low and mands increased. These results suggest that dense NCR schedules may alter establishing operations that result in not only suppression of problem behavior but also interference with the acquisition of appropriate behavior. Thus, the strengthening of socially appropriate behaviors as replacements for problem behavior during NCR interventions might best be achieved if the NCR schedule is first thinned.