|Comparative Behavior Analysis: Toward a Cross-species Analysis of Adaptive Choice
|Monday, May 26, 2008
|1:30 PM–2:50 PM
|Area: EAB; Domain: Basic Research
|Chair: Rachelle L. Yankelevitz (University of Florida)
|Abstract: Cross-species continuity in behavior patterns is often assumed in behavior analysis, yet very little research has been directed at species comparisons per se. The present session brings together four lines of research on choice across three species (pigeons, rats, humans), calling attention to methodological and conceptual issues in comparing behavior across species.
|Delay-Amount Tradeoffs by Pigeons and Rats.
|JAMES E. MAZUR (Southern Connecticut State University), Dawn R. Biondi (Southern Connecticut State University)
|Abstract: An adjusting-delay procedure was used to study the choices of pigeons and rats when both delay and amount of reinforcement were varied. In different conditions, the choice alternatives included 1 versus 2 reinforcers, 1 versus 3 reinforcers, and 3 versus 2 reinforcers. The delay to one alternative (the standard alternative) was kept constant in a condition, and the delay to the other (the adjusting alternative) was increased or decreased many times a session so as to estimate an indifference point—a delay at which the two alternatives were chosen about equally often. Indifference functions were constructed by plotting the adjusting delay as a function of the standard delay for each pair of reinforcer amounts. Consistent with a hyperbolic decay equation, but not with an exponential equation, the slopes of the indifference functions depended on the ratios of the two reinforcer amounts for both pigeons and rats. However, quantitative differences in the data from the two species suggest possible differences in the rates at which reinforcer strength decreases with increasing delay for these species.
|Saving the Best for Last? Cross-species Analysis of Choices between Reinforcer Sequences.
|LEONARDO F. ANDRADE (University of Florida), Timothy D. Hackenberg (University of Florida)
|Abstract: When given choices between sequences of reinforcers distributed over time, humans and non-humans show different patterns of preference: humans tend to prefer sequences that improve over time whereas non-humans tend to prefer sequences that worsen over time (i.e., sequences with more-highly valued reinforcers available early). The differences in performance may be due to fundamental differences in the way reinforcer sequences contribute to reinforcer value. Alternatively, the differences may be attributed to methodological differences, specifically in the nature of the reinforcers used with humans (hypothetical or conditioned reinforcers) and non-humans (consumable reinforcers). The aim of the present study was to compare choice patterns across pigeons and humans between sequences of token and consumable reinforcers that provided the same overall rate, delivered at different delays. The consumable reinforcers were mixed grain and video clips for pigeons and humans, respectively. The results showed generally similar choice patterns across species, with both preferring sequences with the shortest delay to the initial reinforcer in the series. The results are consistent with prior data on temporal discounting with non-humans but differ from prior data with hypothetical reinforcers with humans.
|Varying the Costs of Sunk Costs in Pigeons and People.
|RAUL AVILA (National University of Mexico), Rachelle L. Yankelevitz (University of Florida), Timothy D. Hackenberg (University of Florida)
|Abstract: While pigeons’ performance in a sunk-cost task depends, among other variables, of the relative effort required by the task, humans’ data are insufficient to sustain a fair comparison between the two species. Therefore, in the present study undergraduate students were exposed to a computer-based sunk-cost procedure in which participants earned money according to a variety of fixed-ratio schedules, whose specific values varied among four groups of three participants each. The probability of a given fixed ratio in each trial was systematically varied across conditions. Persistence, the main dependent variable, was defined as the percentage of trials in which the ratios higher than the short one were completed. When the probabilities were .5, .25, .125 and .125 for the two groups with the lowest fixed ratios (2, 10, 20, 40, and 5, 20, 40, 80, respectively) persistence was almost 100%. With the same probabilities but higher fixed ratios (10, 40, 80, 160, and 20, 80, 160, 320) persistence was very low. When the probabilities were changed such that higher ratios in each set were more likely, persistence remained near 100% in the group with the lowest fixed ratios and increased to between 50% and 100% in the group with the highest fixed ratios. These results suggest that sunk-cost decisions are determined by the relative magnitude of the response requirement, and are consistent with prior published data with pigeons. Work currently in progress aims to more systematically explore comparisons with pigeon data.
|Rats, Pigeons, and People Discount Delayed Rewards, But...
|LEONARD GREEN (Washington University), Joel Myerson (Washington University), Amanda L. Calvert (Washington University, St. Louis)
|Abstract: The discounting of delayed rewards by rats, pigeons, and people is, in each case, well described by a hyperboloid function. We report studies examining the effect of amount of delayed reward on rate of discounting in all three species. Interestingly, a magnitude effect (in which larger delayed rewards are discounted less steeply than smaller delayed rewards) was observed only with humans. Humans consistently discounted larger delayed rewards more steeply than smaller delayed rewards, regardless of whether those rewards were monetary or directly consumable in nature. In contrast, nonhumans showed equivalent discounting of both large and small rewards as well as of both more- and less-preferred rewards.