Biomedical subjects

Douglas Elliffe

Publications and source records attributed to Douglas Elliffe.

4 recordsLinked to original sources

PubMed2003

Concurrent schedules: reinforcer magnitude effects.

Five pigeons were trained on pairs of concurrent variable-interval schedules in a switching-key procedure. The arranged overall rate of reinforcement was constant in all conditions, and the reinforcer-magnitude ratios obtained from the two alternatives were varied over five levels. Each condition remained in effect for 65 sessions and the last 50 sessions of data from each condition were analyzed. At a molar level of analysis, preference was described well by a version of the generalized matching law, consistent with previous reports. More local analyses showed that recently obtained reinforcers had small measurable effects on current preference, with the most recently obtained reinforcer having a substantially larger effect. Larger reinforcers resulted in larger and longer preference pulses, and a small preference was maintained for the larger-magnitude alternative even after long inter-reinforcer intervals. These results are consistent with the notion that the variables controlling choice have both short- and long-term effects. Moreover, they suggest that control by reinforcer magnitude is exerted in a manner similar to control by reinforcer frequency. Lower sensitivities when reinforcer magnitude is varied are likely to be due to equal frequencies of different sized preference pulses, whereas higher sensitivities when reinforcer rates are varied might result from changes in the frequencies of different sized preference pulses.

Animals↗

PubMed2003

Strict and random alternation in concurrent variable-interval schedules.

Six pigeons responded on pairs of concurrent variable-interval schedules with, in different parts, four different arrangements of alternation between schedules. Following a single switching-key response, alternation was either strict or random, and the alternative presented after a switch (the postswitch alternative) was either signaled by the location of the switching key or unsignaled. Generalized-matching analyses showed little difference in behavior among the different alternation arrangements, except the usual finding of lower sensitivity of response allocation than time allocation was eliminated by arranging random alternation. Patterns of interchangeover times were similar for all arrangements except signaled random alternation. Differences in behavior preceding the different postswitch alternatives were found in the signaled random alternation procedure. Preference was biased towards the color of the signaled postswitch alternative and showed increased sensitivity when the postswitch alternative was to be the one with the higher reinforcer rate. Interchangeover times were substantially shorter when the postswitch alternative was signaled to be different from the current alternative than when it was signaled to be the same. However, when separate reinforcer ratios were calculated for the different postswitch alternatives, those effects were eliminated or greatly reduced. We suggest that, although behavior is indeed influenced by the postswitch alternative, the mechanism is indirect. That is, the distributions of reinforcers between alternatives obtained before each postswitch alternative differ when those alternatives are signaled, and those distributions are discriminated, but the same relations between choice and relative reinforcement hold irrespective of which postswitch alternative is signaled.

Animals↗

PubMed2003

Choice in a variable environment: effects of unequal reinforcer distributions.

Six pigeons were trained in a procedure in which sessions included seven unsignaled components, each offering two pecking keys, and each providing a potentially different reinforcer ratio between the two keys. Across conditions, various combinations of reinforcer ratios and reinforcer-magnitude ratios were used to create unequal reinforcer distributions between the two alternatives when averaged across a session. The results extended previous research using the same basic procedure that had included only reinforcer distributions symmetrical around 1:1. Data analyses suggested that the variables controlling choice operated at a number of levels: First, individual reinforcers had local effects on choice; second, sequences of successive reinforcers obtained at the same alternative (continuations) had cumulative effects; and, third, when these sequences themselves occurred with greater frequency, their effects further cumulated. A reinforcer obtained at the other alternative following a sequence of continuations (a discontinuation) had a large effect and apparently reset choice to levels approximating the sessional reinforcer ratio.

Animals↗

PubMed2002

Concurrent schedules: short- and long-term effects of reinforcers.

Five pigeons were trained on concurrent variable-interval schedules in a switching-key procedure. The overall rate of reinforcement was constant in all conditions, and the ratios of reinforcers obtainable on the two alternatives were varied over seven levels. Each condition remained in effect for 65 sessions, and the last 50 sessions of data from each condition were analyzed. The most recently obtained reinforcer had the largest effect on current preference, but each of the eight previously obtained reinforcers had a small measurable effect. These effects were larger when the reinforcer ratio was more extreme. A longer term effect of reinforcement was also evident, which changed as a function of the reinforcer ratio arranged. More local analyses showed regularities at a reinforcer-by-reinforcer level and large transient movements in preference toward the just-reinforced alternative immediately following reinforcers, followed by a return to stable levels that were related to the reinforcer ratio in effect. The present data suggest that the variables that control choice have both short- and long-term effects and that the short-term effects increased when the reinforcer ratios arranged were more extreme.

Animals↗