Proceedings of the Annual Meeting of the Cognitive Science Society

Serial stay-or-search problems are ubiquitous across manydomains, including employment, internet search, mate search,and animal foraging. For instance, in patch foragingproblems, animals must decide whether to stick with adepleting reward vs search for a new source. The optimalstrategy in patch foraging problems, described by theMarginal Value Theorem (MVT; Charnov, 1976), is to leavethe depleting patch when the local reward rate within a patchmatches the overall long-run reward rate. Many species ofanimals, ranging from birds to rodents, monkeys, andhumans, adhere to this policy in important respects, but tendto overharvest, or stick with the depleting resource too long.Here we attempt to determine the cognitive biases thatunderlie overharvesting in one of these species (the rat). Wecharacterized rat behavior in response to two basicmanipulations in patch foraging tasks: to travel time betweenpatches and depletion rate, and two novel manipulations tothe foraging environment: the size of reward and length ofdelays, and placement of delays (pre- vs. post-reward). Inresponse to the basic manipulations, rats qualitativelyfollowed predictions of MVT, but stayed in patches for longerthan is predicted. In the latter two manipulations, rats deviatedfrom predictions of MVT, exhibiting changes in behavior notpredicted by MVT. We formally tested whether four separatecognitive biases – subjective costs, decreasing marginal utilityfor reward discounting of future reward, and ignoring post-reward delays – could explain overharvesting in the formertwo manipulations and deviations from MVT in the latter two.All of the biases tested explained overharvesting behavior inthe former contexts, but only one bias – in which rats ignorepost-reward delays – also explained deviations from MVTdue to larger rewards with longer delays and due tointroduction of a pre-reward delay. Our results show thatmultiple biases can explain certain aspects of overharvestingbehavior, and, while foraging behavior may be the result ofthe use of multiple biases, inaccurate estimation of post-reward delays likely contributes to overharvesting.