Zentall (2015) summarises a rich literature on experiments showing that analogues of canonical human biases exist in animals. Specifically, he takes the phenomena of

  • justification of effort: rewards which require more effort are overweighted
  • sunk cost fallacy: past effort is weighted in evaluation of future rewards
  • less-is-more effect: high value rewards are valued less if presented along with a low value reward
  • risk neglect: overweighting of low probability but high value rewards
  • base rate neglect: e.g. over-reliance on events which are likely to be false positives

The demonstration of all these phenomena in animals (often birds – pigeons and dogs in Zentall’s own research) presents a challenge to explanations of these biases in human choice. It suggests they are unlikely to be the result of cultural conditioning, social pressure or experience, or elaborate theories (such as theories of probability or cosmic coincidence in the case of suboptimal choice regarding probabilities, see Blanchard, Wilke and Hayden, 2014).

Zentall suggests that these demonstrations compel us to consider that suboptimal choice in the laboratory can only exist because of some adaptive value in the wild, with common mechanisms for multiple biases, or the independent evolution of each bias/heuristic in separate modules. At the end of the paper he presents some loose speculations on the possible adaptive benefit of each of the discussed biases.

Three interesting recent results from Zentall’s lab concern risky choice in pigeons

1. Laude et al (2014) showed that for individual pigeons there was a correlation between degree of suboptimal choice on a gambling task (overweighting of rare but large rewards) and impulsivity as measured by a delay discounting task. As well as seeming to show ‘individual differences’ in pigeon personality, it suggests the possibility of some common factors in these two kinds of choices (choices which experimental human work has found to be dissociable in various ways)

2. Zentall and Stagner (2011) show that the conditioned reinforcer (stimuli which predict reward) are critical in the gambling task (for pigeons). Without these intermediate stimuli, when actions lead directly to reward (still under the same probabilities of outcome), pigeons choose optimally. Zentall suggests that the thought experiment on the human case confirms the generality of this result. Would slot machines be popular without the spinning wheels? Or (my suggestion) the lottery without the ball machine? My speculation is that the promise of insight into the causal mechanism governing outcome is important. We know that human and non-human animals are guided by intrinsic motivation as well as the promise of material rewards (ie as well as being extrinsically motivated). Rats, for example, will press a lever to turn a light on or off, in the absence of the food reward normally used to train lever pressing (Kish, 1955). One plausible explanation for results like this is that our learning systems are configured to seek control or understanding of the world – to be driven by mere curiosity – in order to generate exploratory actions which will, in the long term, have adaptive benefit. Given this, it makes sense if situations where there is the possibility of causal insight – as with the intermediate stimuli in the gambling task – can inspire actions which are less focussed on exploiting know probabilities (i.e. are ‘exploratory’, in some loose sense) even if the promise of causal insight is illusory and the exploratory action are, as defined by the experiment, futile and suboptimal.

3. Pattison, Laude and Zentall (2013) showed that pigeons who were given the opportunity for social interaction (with other pigeons) were less likely to choose the improbable large reward action over lower expected value but more certain reward. Zentall’s suggestion is that the experience of social interaction diminishes the perceived magnitude of the improbable reward, making it seem like a less attractive choice (which makes sense if neglect of the probability an focus on the magnitude is part of the dynamic driving suboptimal choice in this gambling task). Whatever the reason, the result is a reminder that the choices of animals – human and non-human – cannot be studied in isolation from the experience and environment of the organism. This may sound like an obviousity, but discussion of problematic choices (think gambling, or drug use) often conceptualise behaviours as compelled, part of an immutable biological (addiction as disease) or chemical (drugs as inevitably producing catastrophic addiction) destiny. This result, and others (remember Rat Park) give lie to that characterisation.


Blackburn, M., & El-Deredy, W. (2013). The future is risky: Discounting of delayed and uncertain outcomes. Behavioural processes, 94, 9-18.

Blanchard, T. C., Wilke, A., & Hayden, B. Y. (2014). Hot-hand bias in rhesus monkeys. Journal of Experimental Psychology: Animal Learning and Cognition, 40(3), 280-286.

Kish, G.: Learning when the onset of illumination is used as the reinforcing stimulus. J. Comp. Physiol. Psycho. 48(4), 261–264 (1955)

Laude, J.R., Beckmann, J.S., Daniels, C.W., Zentall, T.R., 2014. Impulsivity affects gambling-like choice by pigeons. J. Exp. Psychol. Anim. Behav. Process. 40, 2–11.

Pattison, K.F., Laude, J.R., Zentall, T.R., 2013. Social enrichment affects suboptimal, risky, gambling-like choice by pigeons. Anim. Cogn. 16, 429–434.

Zentall, T.R., Stagner, J.P., 2011. Maladaptive choice behavior by pigeons: an animal analog of gambling (sub-optimal human decision making behavior). Proc. R. Soc. B: Biol. Sci. 278, 1203–1208.

Zentall, T. R. (2015). When animals misbehave: analogs of human biases and suboptimal choice. Behavioural processes, 112, 3-13.