Choice, optimal foraging, and the delay-reduction hypothesis

Abstract Behaving organisms are continually choosing. Recently the theoretical and empirical study of decision making by behavioral ecologists and experimental psychologists have converged in the area of foraging, particularly food acquisition. This convergence has raised the interdisciplinary question of whether principles that have emerged from the study of decision making in the operant conditioning laboratory are consistent with decision making in naturally occurring foraging. One such principle, the “parameter-free delay-reduction hypothesis, ” developed in studies of choice in the operant conditioning laboratory, states that the effectiveness of a stimulus as a reinforcer may be predicted most accurately by calculating the decrease in time to food presentation correlated with the onset of the stimulus, relative to the length of time to food presentation measured from the onset of the preceding stimulus. Since foraging involves choice, the delay-reduction hypothesis may be extended to predict aspects of foraging. We discuss the strategy of assessing parameters of foraging with operant laboratory analogues to foraging. We then compare the predictions of the delay-reduction hypothesis with those of optimal foraging theory, developed by behavioral ecologists, showing that, with two exceptions, the two positions make comparable predictions. The delay-reduction hypothesis is also compared to several contemporary pscyhological accounts of choice. Results from several of our experiments with pigeons, designed as operant conditioning simulations of foraging, have shown the following: The more time subjects spend searching for or traveling between potential food sources, the less selective they become, that is, the more likely they are to accept the less preferred outcome; increasing time spent procuring (“handling”) food increases selectivity; how often the preferred outcome is available has a greater effect on choice then how often the less preferred outcome is available; subjects maximize reinforcement whether it is the rate, amount, or probability of reinforcement that is varied; there are no significant differences between subjects performing under different types of deprivation (open vs. closed economies). These results are all consistent with the delay-reduction hypothesis. Moreover, they suggest that the technology of the operant conditioning laboratory may have fruitful application in the study of foraging, and, in doing so, they underscore the importance of an interdisciplinary approach to behavior.