State-Dependent Decisions Cause Apparent Violations of Rationality in Animal Choice

Abstract

Normative models of choice in economics and biology usually expect preferences to be consistent across contexts, or “rational” in economic language. Following a large body of literature reporting economically irrational behaviour in humans, breaches of rationality by animals have also been recently described. If proven systematic, these findings would challenge long-standing biological approaches to behavioural theorising, and suggest that cognitive processes similar to those claimed to cause irrationality in humans can also hinder optimality approaches to modelling animal preferences. Critical differences between human and animal experiments have not, however, been sufficiently acknowledged. While humans can be instructed conceptually about the choice problem, animals need to be trained by repeated exposure to all contingencies. This exposure often leads to differences in state between treatments, hence changing choices while preserving rationality. We report experiments with European starlings demonstrating that apparent breaches of rationality can result from state-dependence. We show that adding an inferior alternative to a choice set (a “decoy”) affects choices, an effect previously interpreted as indicating irrationality. However, these effects appear and disappear depending on whether state differences between choice contexts are present or not. These results open the possibility that some expressions of maladaptive behaviour are due to oversights in the migration of ideas between economics and biology, and suggest that key differences between human and nonhuman research must be recognised if ideas are to safely travel between these fields.

Intrasexual competition among females and the stabilization of a conspicuous colour polymorphism in a Lake Victoria cichlid fish

“…We chose this two-choice context, rather than a three-choice context, because, although this was not our primary objective, in the former situation one can also examine whether the degree of aggression bias differs between the two alternative morphs. This is not possible in a three-choice context because any possible bias for own morph relative to morph A is affected by the presence of morph B and vice versa (Schuck-Paim et al 2004). The two stimulus pairs were selected from standard length-matched stimulus trios (OB, P and WB).…”

Do we expect natural selection to produce rational behaviour?

“…Schuck-Paim et al 2004 show that uncontrolled variation in state can produce behaviour that appears to be irrational. Houston et al (2007) show how state-dependent effects can produce apparently irrational behaviour even when an animal's choice is measured in the same state.…”

“…Their findings hold considerable implications for the comparison of choice behaviour across species. Schuck-Paim et al (2004) show that, at least in some cases, seemingly irrational behaviour in animals can be explained purely as a function of state-dependent preferences. As examples, we discuss work on grey jays (Waite 2001a) and rufous hummingbirds .…”

“…This predicts that an individual will be more likely to choose a low-quality, cheap item over a high-quality, expensive one if the individual has already experienced a choice between items of similar quality, but with a smaller difference in cost. However, as Schuck-Paim et al (2004) pointed out, it was not just the previous context in which decisions had been made that differed between the two treatment groups. During the initial phase of the experiment, the jays in context A had gained more than twice as many rewards as those individuals in context B.…”

To Err Is (Not Only) Human: Fallibility as a Window Into Primate Cognition

“…Decoy effects have been documented in situations where human consumers evaluate products (e.g., Pettibone & Wedell, 2000;Wedell, 1991) and evaluate mate choices (Sedikides, Ariely, & Olsen, 1999). There is also evidence that animals may be affected by decoy stimuli (e.g., honeybees : Shafir, Waite, & Smith, 2002;hummingbirds: Bateson, Healy, & Hurly, 2002;Hurly & Oseen, 1999;starlings: Bateson, 2002;Schuck-Paim, Pompilio, & Kacelnik, 2004;cats: Scarpi, 2011).…”