Determinants of pausing under variable-ratio schedules: Reinforcer magnitude, ratio size, and schedule configuration

Pigeons pecked a key under two-component multiple variable-ratio schedules that offered 8-s or 2-s access to grain. Phase 1 assessed the effects of differences in reinforcer magnitude on postreinforcement pausing, as a function of ratio size. In Phase 2, postreinforcement pausing and the first five interresponse times in each ratio were measured as a function of differences in reinforcer magnitude under equal variable-ratio schedules consisting of different configurations of individual ratios. Rates were also calculated exclusive of postreinforcement pause times in both phases. The results from Phase 1 showed that as ratio size increased, the differences in pausing educed by unequal reinforcer magnitudes also increased. The results of Phase 2 showed that the effects of reinforcer magnitude on pausing and IRT durations were a function of schedule configuration. Under one configuration, in which the smallest ratio was a fixed-ratio 1, pauses were unaffected by magnitude but the first five interresponse times were affected. Under the other configuration, in which the smallest ratio was a fixed-ratio 7, pauses were affected by reinforcer magnitude but the first five interresponse times were not. The effect of each configuration seemed to be determined by the value of the smallest individual ratio. Rates calculated exclusive of postreinforcement pause times were, in general, directly related to reinforcer magnitude, and the relation was shown to be a function of schedule configuration.     

Within-session meal-size effects on induced drinking.

As a control for the effects of session duration and hunger on the relation between food magnitude and induced drinking, four food-deprived rats were exposed to a variable-time 50-s schedule of food delivery in which the size of each food delivery varied randomly within sessions. Food-related behavior and schedule-induced drinking per opportunity were examined as functions of meal size and postfood time. All rats showed an inverted-U-shaped relation between drinking per opportunity and meal size. This relation was caused by variation in the percentage of intervals that contained drinking and by variation in the number of drinking bouts per interval, rather than by bout duration or by the amount of drinking within those intervals that actually contained drinking. Head-in-feeder time increased linearly with meal size. Schedule-induced drinking was entrained by food delivery in 3 of 4 subjects; the entrainment was due to regulation of the starting time of each drinking bout rather than to regulation of bout duration.     

Interpersonal contingencies: Performance differences and cost-effectiveness

Three reinforcement contingencies were compared with regard to performance differences and cost-effectiveness (i.e., responses per unit reinforcer). Pairs of college students were studied under individual, cooperative, or competitive contingencies using a concurrent setting that included one of these three contingencies as one alternative and a lower paying individual contingency as the other alternative. With the individual and the cooperative contingencies, overall response rates were typically high; under competitive contingencies the overall response rates were substantially lower. Subjects responded at very high rates when competing, but chose not to compete most of the time. Competition and cooperation produced the most cost-effective responding, assessed as the number of responses made per $.01 of reinforcer. High overall rates of competitive responding were obtained when the contests were longer and the lower paying alternative contingency was not available.     

Choice behavior of rats in a concurrent-chains schedule: Amount and delay of reinforcement

Rats were exposed to concurrent-chains schedules in which the terminal links were equal fixed-interval schedules terminating in one or three food pellets. Choice proportions for large reward increased with increases in delay intervals programmed on fixed-interval schedules and supported the predictions derived from a general choice model originally formulated by Fantino and later developed by Navarick and Fantino. In addition, a functional equivalence of two alternatives was established by increasing delay intervals with large reward, whereas delay intervals for small reward were held constant. Functionally equivalent delay intervals with large reward, for each delay interval with small reward, can be described by a power function with exponent smaller than 1.0. A better prediction of choice proportions resulted when this function was used to derive predicted choice proportions.     

Instructed versus shaped human verbal behavior: Interactions with nonverbal responding

Undergraduate students' presses on left and right buttons occasionally made available points exchangeable for money. Blue lights over the buttons were correlated with multiple random-ratio random-interval components; usually, the random-ratio schedule was assigned to the left button and the random-interval to the right. During interruptions on the multiple schedule, students filled out sentence-completion guess sheets (e.g., The way to earn points with the left button is to...). For different groups, guesses were shaped with differential points also worth money (e.g., successive approximations to “press fast” for the left button), or were instructed (e.g., Write “press slowly” for the left button), or were simply collected. Control of rate of pressing by guesses was examined in individual cases by reversing shaped or instructed guesses, by instructing pressing rates, and/or by reversing multiple-schedule contingencies. Shaped guesses produced guess-consistent pressing even when guessed rates opposed those characteristic of the contingencies (e.g., slow random-ratio and fast random-interval rates), whereas guesses and rates of pressing rarely corresponded after unsuccessful shaping of guesses or when guessing had no differential consequences. Instructed guesses and pressing were inconsistently related. In other words, when verbal responses were shaped (contingency-governed), they controlled nonverbal responding. When they were instructed (rule-governed), their control of nonverbal responding was inconsistent: the verbal behavior sometimes controlled, sometimes was controlled by, and sometimes was independent of the nonverbal behavior.     

Mirror pecking and timeout under a multiple fixed-ratio schedule of food delivery

Pigeons were trained to peck a key under a multiple fixed-ratio 25 fixed-ratio 175 schedule of food presentation. In the first condition, either a mirror or the opportunity to produce a 30-second timeout were available. In a second condition, mirror and timeout availability were reversed for the two groups. Following a return to the initial condition, mirror and timeout keys were presented together for all birds. Mirror and timeout responses occurred predominantly in the pause in the larger fixed-ratio component, regardless of whether the opportunities for the two responses were available singly or together. Mirror responding occurred in a greater proportion of the pauses than did timeouts. When the opportunities for both mirror pecking and timeout were available concurrently, they occurred with probabilities similar to those under the single conditions. Within the pause itself, mirror responses most frequently occurred immediately after reinforcement. Timeouts occurred most frequently toward the end of the pause, and some timeouts occurred in the early part of the run. Longer preratio pausing occurred in the larger fixed-ratio component in the conditions in which the mirror was present, whether or not any mirror pecks were recorded.     

Effects of d-amphetamine and pentobarbital under concurrent fixed-ratio schedules.

Pigeons were studied under a two-key concurrent fixed-ratio schedule of food presentation. During the first five sessions, the fixed-ratio requirements were 30 responses on one key (major key) and 120 responses on the other key (minor key): responding occurred almost exclusively on the major key. When the fixed-ratio requirements were then made equal at 30 responses on both keys, responding continued to predominate on the major key. The asymmetric distribution of responses persisted when the concurrent fixed-ratio fixed-ratio schedule was interrupted with periods during which the major key was associated with extinction while the other key remained associated with a fixed-ratio schedule. Additionally, in some subjects the fixed-ratio requirements were increased. These schedule modifications decreased the asymmetry in responding but did not eliminate it. d-Amphetamine decreased rates on both keys and slightly increased the asymmetric distribution of responses, while pentobarbital reversed the distribution of responses by increasing low rates and decreasing high rates. The pigeons maintained their original asymmetric distribution of responses during the 1 1/2-year-long study, despite schedule alterations and drug administrations.     

Effects of d-amphetamine, cocaine, and phencyclidine on the acquisition of response sequences with and without stimulus fading.

In each of three components of a multiple schedule, monkeys were required to emit a different sequence of four responses in a predetermined order on four levers. Sequence completions produced food on a fixed-ratio schedule. Errors produced a brief timeout. One component of the multiple schedule was a repeated-acquisition task where the four-response sequence changed each session (learning). The second component of the multiple schedule was also a repeated-acquisition task, but acquisition was supported through the use of a stimulus-fading procedure (faded learning). In a third component of the multiple schedule, the sequence of responses remained the same from session to session (performance). At higher doses, d-amphetamine, cocaine, and phencyclidine decreased the overall rate of responding and increased the percent errors in all three components. At lower doses, however, the three drugs produced selective effects on errors. Errors were increased in the learning component at lower doses than those required to disrupt the behavior in the faded-learning component. The performance component tended to be the least sensitive to disruptive drug effects. The data are consistent with the view that stimulus fading can modulate the effects of drugs on acquisition.     

Preference for unsegmented interreinforcement intervals in concurrent chains

Five pigeons were trained under concurrent-chain schedules in which a pair of independent, concurrent variable-interval 60-s schedules were presented in the initial link and either both variable-interval or both fixed-interval schedules were presented in the terminal link. Except for the baseline, one of the terminal-link schedules was always a two-component chained schedule and the other was either a simple or a tandem schedule of equal mean interreinforcement interval. The values of the fixed-interval schedules were either 15 s or 60 s; that of the variable-interval schedules was always 60 s. A 1.5-s changeover delay operated during the initial link in some conditions. The pigeons preferred a simple or a tandem schedule to a chain. For the fixed-interval schedules, this preference was greater when the fixed interval was 60 s than when it was 15 s. For the variable-interval schedules, the preferences were less pronounced and occurred only when the changeover delay was in effect. For a given type of schedule and interreinforcement interval, similar preferences were obtained whether the nonchained schedule was a tandem or simple schedule. The changeover delay generally inflated preference and lowered the changeover rate, especially when the terminal-link schedules were either short (15 s) or aperiodic (variable-interval). The results were consistent with the notion that segmenting the interreinforcement interval of a schedule into a chain lowers the preference for it.     

Using activity schedules to promote varied application use in children with autism

We evaluated the effects of an activity schedule embedded within an iPad on varied play across applications. After establishing a pattern of repetitive gameplay, we taught three children with autism to follow the activity schedule using physical guidance. All participants increased their varied play to four applications per session and demonstrated independent and accurate activity schedule usage. The activity schedule was removed, and responding decreased to baseline levels, demonstrating the activity schedule's control over varied responding. The activity schedule was reintroduced and participant responding maintained when engaging with novel applications.