Concurrent schedules: Effects of time- and response-allocation constraints

Five pigeons were trained on concurrent variable-interval schedules arranged on two keys. In Part 1 of the experiment, the subjects responded under no constraints, and the ratios of reinforcers obtainable were varied over five levels. In Part 2, the conditions of the experiment were changed such that the time spent responding on the left key before a subsequent changeover to the right key determined the minimum time that must be spent responding on the right key before a changeover to the left key could occur. When the left key provided a higher reinforcer rate than the right key, this procedure ensured that the time allocated to the two keys was approximately equal. The data showed that such a time-allocation constraint only marginally constrained response allocation. In Part 3, the numbers of responses emitted on the left key before a changeover to the right key determined the minimum number of responses that had to be emitted on the right key before a changeover to the left key could occur. This response constraint completely constrained time allocation. These data are consistent with the view that response allocation is a fundamental process (and time allocation a derivative process), or that response and time allocation are independently controlled, in concurrent-schedule performance.     

The interaction between stimulus and reinforcer control on remembering.

In a symbolic matching-to-sample task, 6 pigeons obtained food by pecking a red side key when the brighter of two white lights had been presented on the center key and by pecking a green side key when the dimmer of two white lights had been presented on the center key. Across Part 1 and Parts 6 to 10, the delay between sample-stimulus presentation and the availability of the choice keys was varied between 0 s and 25 s. Across Parts 1 to 5, the delay between the emission of a correct choice and the delivery of a reinforcer was varied between 0 s and 30 s. Although increasing both types of delay decreased stimulus discriminability, lengthening the stimulus-choice delay produced a greater decrement in choice accuracy than did lengthening the choice-reinforcer delay. Additionally, the relative reinforcer rate for correct choice was varied across both types of delay. The sensitivity of behavior to the distribution of reinforcers decreased as discriminability decreased under both procedures. These data are consistent with the view, based on the generalized matching law, that sample stimuli and reinforcers interact in their control over remembering.     

Behavioral economics of drug self-administration. II. A unit-price analysis of cigarette smoking.

In behavioral economics, the ratio of response requirement to reinforcer magnitude is referred to as unit price. Previous research with nonhuman subjects has demonstrated that (a) comparable amounts of food are consumed at the same unit price even though different response requirements and reinforcer magnitudes comprise that unit price and (b) increases in unit price decrease food consumption in a positively decelerating fashion. The present study assessed the generality of these findings to the cigarette smoking of 5 human volunteers. During approximately 18 3-hr sessions, various combinations of response requirement (fixed-ratio 200, 400, and 1,600) and reinforcer magnitude (1, 2, and 4 puffs per bout) were arranged. Consumption (i.e., the number of puffs) generally was comparable at the same unit price independent of the response requirement and reinforcer magnitude comprising that unit price. In addition, increasing unit price generally decreased consumption in a positively decelerating fashion. These results extend the generality of the unit-price analysis to human cigarette smoking. Moreover, these results further support the position that reinforcer magnitude and response requirement are functionally equivalent and interact to determine consumption. The concept of unit price, by integrating and summarizing the effects of those two operations, provides a more parsimonious explanation of the results than do separate evaluations of the effects of response requirement and reinforcer magnitude.     

Economic substitutability of electrical brain stimulation, food, and water.

Concurrent variable-ratio schedules of electrical brain stimulation, food, and water were paired in various combinations as reinforcement of rats' lever presses. Relative prices of the concurrent reinforcers were varied by changing the ratio of the response requirements on the two levers. Economic substitutability, measured by the sensitivity of response ratio to changes in relative price, was highest with brain stimulation reinforcement of presses on both levers and lowest with food reinforcement of presses on one lever and water reinforcement of presses on the other. Substitutability with brain stimulation reinforcement of presses on one lever and either food or water reinforcement for presses on the other was about as high as with brain stimulation for presses on both levers. Electrical brain stimulation for rats may thus serve as an economic substitute for two reinforcers, neither of which is substitutable for the other.     

Performance of humans in concurrent avoidance/positive-reinforcement schedules

Performance maintained under concurrent schedules consisting of a variable-interval avoidance component and a variable-interval positive-reinforcement component was studied in three human subjects using points exchangeable for money as the reinforcer. The rate of responding in the avoidance component increased, and the rate of responding in the positive-reinforcement component declined, as a function of the frequency of point-losses avoided in the avoidance component. The performance of all three subjects conformed to equations proposed by Herrnstein to describe behavior in concurrent schedules. The logarithms of the ratios of the response rates in the two components, and the logarithms of the ratios of the times spent in the two components, were linearly related to the logarithms of the ratios of the frequency of loss avoidance in the avoidance component to the frequency of reinforcement in the positive-reinforcement component. When a changeover delay of 5.0 sec was imposed, the slopes of the linear functions were close to 1.0 in the case of two subjects, whereas the third subject exhibited significant undermatching. For two subjects the changeover delay was then reduced to 2.0 sec; in both cases the slopes of the linear functions were lower than under the 5.0-sec condition. One subject participated in a third phase, in which no changeover delay was imposed; there was a further reduction in the slopes of the linear functions.     

Interval and ratio reinforcement of a complex sequential operant in pigeons

Pigeons were required to produce exactly four pecks on each of two keys in any order for reinforcement. Correct response sequences were reinforced on either fixed-interval two-minute or fixed-ratio four schedules, with each correct sequence treated as a single response. Each pigeon developed a particular dominant sequence that accounted for more than 80% of all sequences. Sequence stereotypy was relatively unaffected by the temporal properties of the fixed-interval and fixed-ratio schedules. Response time (time from the first response in each sequence to the last) was also relatively unaffected by the temporal properties of the schedules. In contrast, response latency (time from end of one sequence to the beginning of the next) was markedly affected by the schedules. Latencies were long early in the interreinforcement interval and got shorter as the interreinforcement interval progressed. These data suggest that stereotyped response sequences become functional behavioral units, resistant to disruption or alteration by reinforcement variables that ordinarily influence the temporal spacing of individual responses.     

Choice and multiple reinforcers

Pigeons chose between equivalent two-component mixed and multiple terminal-link schedules of reinforcement in the concurrent-chains procedure. The pigeons preferred the multiple schedule over the mixed when the components of the compound schedules were differentiated in terms of density of reinforcement, but the pigeons were indifferent when the components were differentiated in terms of number of reinforcers per cycle. Taken together, these results indicate that a local variable, the interval to the first reinforcer, but not a molar variable, the number of reinforcers, was sufficient to differentiate the components and thereby evoke preference.     

Stimulus discriminability in free-operant and discrete-trial detection procedures.

Six pigeons were trained to discriminate different light intensities in four experimental procedures. Experiment 1 compared stimulus discriminability in a yes-no signal-detection task with discriminability measures obtained from two free-operant procedures. Discriminability estimates were significantly lower in the detection procedure. Experiment 2 showed this lowered discriminability to be a function of the delay between stimulus presentation and the availability of the choice-response keys in the standard detection task. In addition, reinforcement sensitivity was lowest when correct choice responses were intermittently, rather than continuously, reinforced.     

Human performance on conjunctive fixed-interval fixed-ratio schedules

Eighteen young adults performed a lever-pulling task for money. Subjects were initially exposed to a fixed-interval 80-second schedule and subsequently to one of three conjunctive schedules in which the added fixed-ratio requirement was set at either 10, 80, or 120 responses. Three fixed-interval response patterns emerged: high constant rate, intermediate rate, or low rate, with most subjects displaying the last. Conjunctive performance was related to the subjects' prior fixed-interval patterns and the conjunctive ratio requirements. Low-rate subjects tended to optimize reinforcement (maximum reinforcers for minimum responses) on conjunctive schedules. Response rate was directly related to ratio requirements. Subjects' performance closely corresponded to their verbal statements of the contingencies.     

FI SCHEDULES AND PERSISTENCE AT GAMBLING IN THE U.K. BETTING OFFICE

This study reports on the direct observations of customers in two U.K. betting offices gambling on horse and dog races. These observations revealed that bets were more frequently placed in the last minutes just prior to the start (the OFF), and that this was caused by high-frequency gamblers (customers who had eight or more bets in a session) consistently placing their bets in the last two minutes prior to the OFF. Low-frequency gamblers (three or fewer bets/session) avoided this time period placing their bets earlier, or after the OFF, i.e., on a later race. It was argued that the betting behavior of the “gamblers” could not be explained either in terms of “skillful betting” or solely in terms of variable ratio schedules but was more adequately accounted for in terms of an interval schedule. It was further suggested that time-based schedules might be of heuristic value in generally understanding persistence at gambling while losing.