When rate maximization is impulsive

Abstract

Although optimal foraging theory predicts that natural selection should favor animal behaviors that maximize long-term rate of gain, behaviors observed in the laboratory tend to be impulsive. In binary-choice experiments, despite the long-term gain of each alternative, animals favor short handling times. Most explanations of this behavior suggest that there is hidden rationality in impulsiveness. Instead, we suggest that simultaneous and mutually exclusive binary-choice encounters are often unnatural and thus immune to the effects of natural selection. Using a simulation of an imperfect forager, we show how a simple strategy (i.e., an intuitive model of animal behavior) that maximizes long-term rate of gain under natural conditions appears to be impulsive under operant laboratory conditions. We then show how the accuracy of this model can be verified in the laboratory by biasing subjects with a short pre-experiment ad libitum high-quality feeding period. We also show a similar behavioral mechanism results in diet preferences that are qualitatively consistent with the digestive rate model of foraging (i.e., foraging under digestive rate constraints).

Time discounting and time preference in animals: A critical review

“…The disjunction between the observed discount factors and the fundamental facts of foraging behavior has been particularly salient to field biologists, ethologists, and foraging theorists, because they are in the habit of thinking in evolutionary terms (Kacelnik, 2003;Pavlic & Passino, 2010;Stephens & Anderson, 2001;Stephens, Kerr, & Fernández-Juricic, 2004). Because severe discounting ought to be strongly disfavored by natural selection, they are reluctant to accept at face value the notion that animals make such obviously poor choices in their daily lives.…”

“…Thus, delays can be costly even if they pose no special self-control problem. For this reason, several scholars have suggested that animals may avoid delays in intertemporal choice because they wish to avoid the opportunity cost they carry, and not because they lack self-control (Bateson & Kacelnik, 1996;Blanchard et al, 2013;Kacelnik, 2003;Pavlic & Passino, 2010;Stephens & Anderson, 2001). …”

“…Several authors have pointed to the postreward delay (Bateson & Kacelnik, 1996;Blanchard et al, 2013;Pavlic & Passino, 2010;Pearson, Hayden, & Platt, 2010;Stephens & Anderson, 2001). In the animal intertemporal choice task, the overall trial length is generally kept constant by lengthening the postreward delay following SS choices (Fig.…”

“…Bateson and Kacelnik (1996) identified a heuristic that approximates rate-maximizing behavior in many situations and that describes animals' choices quite well: value divided by prereward delay (which they call the expectation of rates, or EoR). EoR produces good behavior in many naturalistic contexts but produces poor behavior in the intertemporal choice task, because it ignores postreward delays (see also Pavlic & Passino, 2010;Stephens & Anderson, 2001;Stephens et al, 2004). The truth is likely to be more complex.…”

“…A theoretical long-term rate-maximizing decision-maker with no impulsivity (i.e., an optimal forager) will prefer an SS to an LL option if the opportunity costs imposed by the LL choice outweigh the its benefits. However, this discounter may, to a naive observer, appear to be impulsive (Bateson & Kacelnik, 1996;Blanchard, Pearson, & Hayden, 2013;Kacelnik, 2003;Namboodiri, Mihalas, Marton, & Hussain Shuler, 2014;Namboodiri, Mihalas, & Shuler, 2014;Pavlic & Passino, 2010;Stephens, 2002;Stephens & Anderson, 2001). …”