Separating response dependency and response-reinforcer contiguity within a recycling conjunctive schedule

A procedure is described which disrupts response-reinforcer contiguity and response dependency and which demonstrates how the location of the response dependency in interval schedules can be regarded as a controlling variable in its own right. Rats' lever pressing produced sucrose on a recycling conjunctive fixed-time 30-second fixed-ratio 1 schedule of reinforcement. Reinforcement occurred only at the end of the fixed-time component on this schedule and only if a response had occurred during that component. This produced a pause-respond-pause pattern during the interreinforcer interval for all animals. When the location of the response dependency was then restricted to a 10-second period in the middle of the fixed-time component, the pattern was accentuated and response rates increased for all animals, while postreinforcement pauses decreased sharply for two animals. When responding was required in the first 10 seconds of the fixed-time component, responding peaked earlier in the interval for all animals. Response rates were slightly below those in the previous conditions, while postreinforcement pauses were between 2 and 6 seconds across animals.     

Operant conditioning of autogrooming in vervet monkeys: Cercopithecus aethiops

Vervet monkeys received food reinforcement contingent on autogrooming. Experiment 1 reinforced grooming on a schedule of increasing intermittency and grooming increased in frequency and duration; with only pauses reinforced, grooming decreased in frequency and duration. Experiment 2 demonstrated differentiation of operant autogrooming; in each session a different single form of grooming was reinforced (for example, grooming the tail only), and that form increased in frequency while other forms became less frequent. In Experiment 3 scratching was succesfully conditioned with a method that selectively reinforced variety in behavior; reinforcement was contingent on a shift in scratching form. In Experiment 4, with no contingencies on grooming, a prefood stimulus did not increase autogrooming whether or not grooming had previously resulted in contingent reinforcement. The form of conditioned autogrooming resembled the form of unconditioned autogrooming. The discussion suggests how reinforcement principles can account for changes in the topography of operant behavior.     

The sleeping giant: Reinforcement schedules

Schedule research has been the core of operant conditioning, but it is no longer an active area, at least with respect to its traditional focus of describing and explaining moment-to-moment behavior. Yet schedules are central in psychology: Not only do they establish lawful behavior, but they also play a major role in determining the effects of other variables. The reason for the decline appears to be primarily theoretical, in that the work seems not to have led to meaningful integration. The search for controlling variables brought into play by schedule specification has proven unsuccessful, and a catalog of all possible schedule effects is of limited interest. The paper reviews the reasons for the contemporary state of affairs. One prediction about future developments is that instead of revealing component variables and their modes of interaction, schedule effects will be treated as basic empirical laws. Theory will take the form of abstract statements that integrate these separate laws by reference to higher-order principles rather than by reduction to supposedly simpler component variables.     

Effects of methadone on alternative fixed-ratio fixed-interval performance: latent influences on schedule-controlled responding.

Effects of methadone on pigeons' key pecking were examined under four conditions selected to analyze the control of behavior under alternative fixed-ratio fixed-interval schedules. In Condition 1, pigeons pecked under one of three different alternative schedules (alternative fixed-ratio 50 fixed-interval 90 s, alternative fixed-ratio 75 fixed-interval 90 s and alternative fixed-ratio 200 fixed-interval 90 s) each week. In Condition 2, fixed-ratio 50 or fixed-ratio 75 schedules were in effect during baseline sessions, and alternative fixed-ratio 50 fixed-interval 90-s or alternative fixed-ratio 75 fixed-interval 90-s schedules were in effect during sessions in which methadone was administered. In Condition 3, effects of methadone on key pecking maintained under fixed-ratio 50 and fixed-ratio 75 schedules were examined, whereas in Condition 4 the effects of methadone on key pecking under a fixed-interval 90-s schedule as well as fixed-ratio 50 and fixed-ratio 75 schedules were investigated. Control by the fixed-interval contingency was assessed by computing the proportion of total session reinforcers delivered under the fixed-interval schedule. Methadone administration (0.5-4.0 mg/kg) shifted the predominant source of schedule control under the alternative schedule from the fixed-ratio schedule to the fixed-interval contingency. This shift was dependent on methadone dose and fixed-ratio size. Control by the fixed-interval contingency was greatest following extensive exposure to the interval component embedded within the alternative schedule (Condition 1), but was apparent to a lesser degree with even very limited exposure to the alternative fixed-ratio fixed-interval schedule (Condition 2). Interreinforcement intervals comparable to those under fixed-interval schedule were not observed under the fixed-ratio schedules presented alone (Condition 3). Repeated exposure to the fixed-interval contingency outside the context of the alternative fixed-ratio fixed-interval schedule did not engender performance changes under a fixed-ratio schedule which would mimic those of increased fixed-interval contingency control (Condition 4). These data suggest that drug administration can be used to unmask the influence of contingencies that are latent under baseline conditions and reveal influences of both past and present environmental variables.     

Concurrent-schedule performance in dairy cows: persistent undermatching.

Performance of dairy cows responding under concurrent variable-interval variable-interval schedules of food delivery was examined, with results analyzed in terms of the generalized matching equation. In Experiment 1, bias measures indicated that crushed barley was preferred over meatmeal when these foods were available under the alternative schedules. For whole-session data, substantial undermatching of response and time-allocation ratios to obtained reinforcement ratios was evident. Postreinforcement pause time ratios approximately matched obtained reinforcement rates. Subtracting these times from total time-allocation values yielded net time-allocation ratios that undermatched obtained reinforcement ratios to a greater degree than did whole-session time-allocation ratios. In Experiment 2, substantial undermatching was evident when the same foods (hay for 2 cows, crushed barley for 2 others) were available under the alternative schedules. Food-related activities and other defined behavior not related to food were quantified by direct observation, and were found to occupy a substantial proportion (roughly 40% to 80%) of experimental sessions. Subtracting the time spent in these activities from the time allocated to each component schedule did not reduce the degree of undermatching obtained. Across all conditions in both experiments, slopes of regression lines relating behavioral outputs to environmental inputs characteristically were below 0.6, which agrees with prior findings and suggests that, contrary to suggestions in the literature, undermatching in dairy cows is not the result of using different foods under alternative schedules or differential pausing under those schedules.     

Representing within-session response rates proportionally and entirely.

In this technical article, methods for collecting and representing response rates maintained by schedules of reinforcement are presented. First, the time in a session that each important event (e.g., responses, reinforcers) occurs is collected and stored by a computer. Another computer program is used, then, to convert each response to a percentage of the total responses in a session and to plot these percentages cumulatively as a function of the time in the session that they occurred. In this manner, response rates may be expressed proportionally (i.e., using the same y-axis scale regardless of absolute response rate) without requiring the arbitrary selection of an interval over which responses are aggregated and expressed relative to the entire-session rate. A property of these records is that deviations in the slope of the obtained record from the diagonal, which connects (x, y) = (start of session, 0%) to (x, y) = (end of session, 100%), occurring at any point and for any duration, represent changes in the local response rate from the entire-session rate. This method of representing ongoing responding is illustrated by several records of key pecking of a pigeon on a variable-interval 60-s schedule of food reinforcement. Relative local response rates were also computed from these data at several levels of resolution (i.e., the time over which responses were aggregated), including the level typically employed by those interested in within-session changes in response rates.     

The effects of varying the distribution of generalization stimuli within a constant range upon the bisection of a sound-intensity interval by rats

Two male, albino rats were trained on a two-valued, self-paced, discrete-trials auditory discrimination. In the presence of a high-intensity stimulus (90 decibels SPL, 4 kiloHertz), response A was reinforced; in the presence of a low-intensity stimulus (50 decibels SPL, 4 kiloHertz), response B was reinforced. When discrimination performance was asymptotic, stimuli intermediate in intensity were presented with the training stimuli in a maintained generalization paradigm. Generalization gradients were derived from the relative frequencies of response A in the presence of each stimulus. A relative frequency of 0.50 was then determined and used as the bisection point of the intensity interval defined by the 90- and 50-decibel stimuli. The bisection point varied with the distribution of the stimuli presented in generalization. This effect was similar to context effects seen in human psychophysics.     

Factors influencing responding under multiple schedules of conditioned and unconditioned reinforcement

Two experiments examined pigeons' responses under multiple schedules of conditioned and unconditioned reinforcement. In one component, responses produced food according to a fixed-interval schedule; in a second component, responses produced brief stimuli according to a fixed-ratio schedule. When brief-stimulus presentations were paired with food in the first component, rates in the second component were usually higher than 10 responses per minute. When pairing in the first component was eliminated, responding continued to be maintained in the second component. Elimination of food presentation from the first component substantially decreased responding in the second component, even though the brief stimulus had not been paired with food. Experiment II demonstrated that response rate was affected by the duration of both the second component and the brief stimulus. The results suggest that three conditions are important in maintaining responding with brief-stimulus presentations: (1) pairing the brief stimulus, at least initially, with food, (2) maintaining unconditioned reinforcement in one component, and (3) employing optimal brief-stimulus and component durations.     

Fixed versus variable sequences of food and stimulus presentation in second-order schedules

Three pigeons were exposed to a second-order schedule in which the behavior specified by a fixed-interval component schedule was reinforced according to a ratio overall schedule. The completion of components not followed by food was signalled by a brief stimulus never paired with food. Food and the stimulus occurred in a random sequence or in fixed alternation, but the overall schedules (variable ratio 2 or fixed ratio 2) ensured that an equal number of food and brief-stimulus presentations occurred in each session. The control exerted by the food and by the brief stimulus was measured by overall response rates, mean pauses, frequency distributions of pauses, and response patterning across components. In general, the stimulus controlled patterns of behavior more similar to those controlled by food when food and the stimulus occurred in a random sequence than when they occurred in fixed alternation.     

Conjunctive schedules of response-dependent and response-independent reinforcement

Pigeons received food when they emitted the number of responses specified by a fixed-ratio schedule, and the time specified by a fixed-time schedule had elapsed. The order of meeting the response and time requirements was irrelevant. In different conditions, stimuli signalled completion of one, both, or neither requirement. Ratio size interacted with stimulus condition to determine performance. When a stimulus signalled the end of the fixed-time period, under all ratios the birds tended to respond after the stimulus appeared. When stimuli followed both components, small ratios produced responding during the fixed-time period, and other ratios resulted in responses after the time period had elapsed. With either no stimulus changes, or with a stimulus correlated with completion of the ratio alone, responding first increased and then decreased as the ratio increased. Low and high ratios produced stable response frequencies and patterns in successive intervals. Intermediate ratios resulted in two types of performance. Intervals with long initial pauses and few responses during the fixed-time period were followed by intervals with short pauses and numerous responses and vice versa. The source of these dynamic effects was hypothesized to be number of responses per reinforcer in one condition and response-reinforcer contiguity in the other.