Resistance to change produced by access to fixed-delay versus variable-delay terminal links

Pigeons' responding was reinforced on a multiple schedule consisting of two two-link chain schedules presented in regular alternation. Responding in initial links (always variable-interval 60-s) produced a key-color change and access to a terminal link. The terminal link for one chain provided food after a fixed delay (fixed-interval or fixed-time); the terminal link for the other provided food after a variable delay (variable-interval or variable-time). The average duration of the terminal-link schedules was varied across conditions, but in every condition the arithmetic mean of the variable-delay terminal-link schedule was equal to the duration of the fixed delay. Response rates were higher in the initial links of the chains with the variable-delay terminal links. Response-decreasing operations (satiation, extinction) were used after performances reached asymptote. Response rates maintained by access to variable-delay terminal links tended to be more resistant to change than were rates maintained by access to fixed-delay terminal links. These results are consistent with the preference for variable- over fixed-interval terminal links observed with concurrent-chains schedules, suggesting (1) that immediacy of reinforcement influences the conditioned reinforcing potency of access to a terminal link and (2) that choice in concurrent chains and resistance of responding to change may be manifestations of the same effect of reinforcement.     

Absence of anticipatory contrast in rats trained on multiple schedules.

Rats were trained on three- and four-component multiple schedules in which two of the components were correlated with identical reinforcement schedules that remained unchanged throughout training. These target components differed in terms of whether their respective following schedules were either higher or lower in value. Unlike corresponding experiments previously reported with pigeons, higher response rates occurred in the target component followed by a higher valued schedule than in the target component followed by the lower valued schedule. Overall contrast effects occurred independently of these sequential effects, but were inconsistent across subjects. The results suggest that the effects of a following schedule of reinforcement are opposite for pigeons and rats, and that one reason previous studies have often failed to show contrast effects with rats is that the effects of the following schedule in rats are in competition with contrast dynamics.     

Responding of pigeons under variable-interval schedules of signaled-delayed reinforcement: effects of delay-signal duration.

Two experiments with pigeons examined the relation of the duration of a signal for delay ("delay signal") to rates of key pecking. The first employed a multiple schedule comprised of two components with equal variable-interval 60-s schedules of 27-s delayed food reinforcement. In one component, a short (0.5-s) delay signal, presented immediately following the key peck that began the delay, was increased in duration across phases; in the second component the delay signal initially was equal to the length of the programmed delay (27 s) and was decreased across phases. Response rates prior to delays were an increasing function of delay-signal duration. As the delay signal was decreased in duration, response rates were generally higher than those obtained under identical delay-signal durations as the signal was increased in duration. In Experiment 2 a single variable-interval 60-s schedule of 27-s delayed reinforcement was used. Delay-signal durations were again increased gradually across phases. As in Experiment 1, response rates increased as the delay-signal duration was increased. Following the phase during which the signal lasted the entire delay, shorter delay-signal-duration conditions were introduced abruptly, rather than gradually as in Experiment 1, to determine whether the gradual shortening of the delay signal accounted for the differences observed in response rates under identical delay-signal conditions in Experiment 1. Response rates obtained during the second exposures to the conditions with shorter signals were higher than those observed under identical conditions as the signal duration was increased, as in Experiment 1. In both experiments, rates and patterns of responding during delays varied greatly across subjects and were not systematically related to delay-signal durations. The effects of the delay signal may be related to the signal's role as a discriminative stimulus for adventitiously reinforced intradelay behavior, or the delay signal may have served as a conditioned reinforcer by virtue of the temporal relation between it and presentation of food.     

Responding of pigeons under variable-interval schedules of unsignaled, briefly signaled, and completely signaled delays to reinforcement

In Experiment 1, three pigeons' key pecking was maintained under a variable-interval 60-s schedule of food reinforcement. A 1-s unsignaled nonresetting delay to reinforcement was then added. Rates decreased and stabilized at values below those observed under immediate-reinforcement conditions. A brief stimulus change (key lit red for 0.5 s) was then arranged to follow immediately the peck that began the delay. Response rates quickly returned to baseline levels. Subsequently, rates near baseline levels were maintained with briefly signaled delays of 3 and 9 s. When a 27-s briefly signaled delay was instituted, response rates decreased to low levels. In Experiment 2, four pigeons' responding was first maintained under a multiple variable-interval 60-s (green key) variable-interval 60-s (red key) schedule. Response rates in both components fell to low levels when a 3-s unsignaled delay was added. In the first component delays were then briefly signaled in the same manner as Experiment 1, and in the second component they were signaled with a change in key color that remained until food was delivered. Response rates increased to near baseline levels in both components, and remained near baseline when the delays in both components were lengthened to 9 s. When delays were lengthened to 27 s, response rates fell to low levels in the briefly signaled delay component for three of four pigeons while remaining at or near baseline in the completely signaled delay component. In Experiment 3, low response rates under a 9-s unsignaled delay to reinforcement (tandem variable-interval 60 s fixed-time 9 s) increased when the delay was briefly signaled. The role of the brief stimulus as conditioned reinforcement may be a function of its temporal relation to food, and thus may be related to the eliciting function of the stimulus.     

IS THERE A DECISIVE TEST BETWEEN MATCHING AND MAXIMIZING?

Reinforcers under typical concurrent variable-interval, variable-ratio schedules may be (a) earned and obtained during the variable-interval component, (b) earned and obtained during the variable-ratio component, or (c) earned during the variable-ratio component and obtained during the variable-interval component. Categories a and b, which have no bearing on matching versus maximizing accounts of choice, were set at zero. The rate of Category c reinforcers and the duration of a changeover delay were varied. Simple matching, which predicts exclusive choice of the variable-interval component, and strict maximizing of overall reinforcement rate, which predicts a bias towards the variable-ratio component, were both disconfirmed: Subjects spent approximately 25% of their time in the variable-ratio component, contrary to the matching prediction, but earned only about one third of the reinforcers predicted by strict maximizing. However, maximizing describes the findings functionally in terms of discounting of delayed reinforcers; matching may describe the data in terms of a restructuring of the alternatives. Matching and maximizing are not competing theories about the fundamental nature of choice, but compatible points of view that may reveal environmental function and behavioral structure.     

Income and choice between different goods

In Experiment 1, 3 rats chose between two simultaneously operating variable-interval schedules, one of which provided saccharin water and the other, food. In five conditions, the absolute (and equal) reinforcement rates provided by the pair of equal-valued schedules were manipulated in the range of 36 to 240 per hour. Experiment 2 was identical to Experiment 1 except that these schedules operated successively, arranged by requiring the rat to stand on the side of the chamber correlated with each schedule. Food/saccharin choice ratios were inversely related to reinforcement rate in both experiments, although this effect was stronger in Experiment 2. When delivery rates were high, preference for food over saccharin often reversed as the session progressed. The results were interpretable in terms of economic accounts of choice (e.g., the minimum-needs hypothesis), as well as in terms of traditional psychological accounts (e.g., matching theory).     

Choice between sequences of fixed-ratio schedules: effects of ratio values and probability of food delivery.

Pigeons were exposed to schedules of food delivery that consisted of two sequential fixed ratios. When alternative sequences provided two food deliveries per 50 responses, the schedule with the shorter initial fixed-ratio value was consistently preferred. Progressively reducing from 1.0 to .25 the probability of food delivery following completion of the second fixed ratio of the sequence with the shorter initial fixed ratio did not reduce preference for this sequence. Moreover, the sequence with the shorter initial fixed ratio also was preferred when the probability of food delivery following completion of the initial ratio in that sequence was progressively reduced from 1.0 to .5, although preference shifted to the alternative when the probability was reduced to 0. These findings suggest that the length of the initial fixed ratio was a primary determinant of choice. Subsequent manipulations demonstrated, however, that when the initial fixed ratios of the two alternatives were equal, changes in the ratio value and probability of food delivery following completion of the second fixed ratio lawfully affected choice.     

Consumption-leisure tradeoffs in pigeons: Effects of changing marginal wage rates by varying amount of reinforcement

Pigeons' rates of responding and food reinforcement under simple random-ratio schedules were compared with those obtained under comparable ratio schedules in which free food deliveries were added, but the duration of each food delivery was halved. These ratio-with-free-food schedules were constructed so that, were the pigeon to maintain the same rate of responding as it had under the simple ratio schedule, total food obtained (earned plus free) would remain unchanged. However, any reduction in responding would reduce total food consumption below that under the simple ratio schedule. These “compensated wage decreases” led to decreases in responding and decreases in food consumption, as predicted by an economic model of labor supply. Moreover, the reductions in responding increased as the ratio value increased (i.e., as wage rates decreased). Pigeons, therefore, substituted leisure for consumption. The relationship between these procedures and negative-income-tax programs is noted.