Monday, August 11, 2008

Chimpanzees use self distraction to cope with impulsivity

ResearchBlogging.orgThis is an interesting and important paper about a strategy for dealing with impulsivity that has not previously been documented in non-humans. Here's the abstract:
It is unknown whether animals, like humans, can employ behavioural strategies to cope with impulsivity. To examine this question, we tested whether chimpanzees (Pan troglodytes) would use self-distraction as a coping strategy in a situation in which they had to continually inhibit responses to accumulating candies in order to earn a greater amount of those rewards. We tested animals in three conditions in which they were sometimes given a set of toys and were sometimes allowed physical access to the accumulating candies. Chimpanzees allowed the rewards to accumulate longer before responding when they could divert their attention to the toys, and they manipulated the toys more when the candies were physically accessible. Thus, chimpanzees engaged in self-distraction with the toys when such behaviour was most beneficial as a coping mechanism.
One of the most persistent ways in which people make poor decisions is by being impulsive. In the behavioural sense, impulsivity amounts to a temporary preference for a smaller reward that is available sooner over a larger one that is available later. (There are more complicated impulsivity constructs in psychiatry and personality psychology - they're not what I'm writing about here.)

This is a dangerous kind of preference to have - it's by definition inconsistent with some of your own preferences over longer ranges, making us open to exploitation, and setting us up for regret. There's a substantial pile of evidence across various species that the discount function describing the decline in the present value of a reward as delay to delivery increases is approximately hyperbolic. Only an exponential curve (so called because the delay term appears as an exponent) has the property that the relative value of rewards at different delays stays constant without ever going to zero. Hyperbolic curves, instead, can lead to temporary preferences (see figure below):

George Ainslie (e.g. 2001) describes a number of strategies that people can use to try to fight inconsistency, including managing attention, preparing emotion, making side-bets and using other committment devices, and chosing
according to rules that connect future rewards and present temptations in different ways. One of his own key experiments (Ainslie 1974) showed
something related to committment as a way of dealing with impulsivity is observed in pigeons: some birds trained that pecking one key would lead to a smaller sooner reward, and another a larger later one, learned to peck an additional key earlier on that had no effect except to remove the temptation of the smaller sooner reward.

This paper is specifically concerned with managing attention as a way of dealing with temptation. As the authors note there is some evidence that human children can adopt self-distraction as a strategy to help them not give into temptation in an experimental setting where refraining from taking an immediately available reward leads to greater reward accumulating later on. Although nobody has attempted to see whether Chimpanzees can do the same thing before, other work suggesting that chimps use behavioural strategies to cope with other kinds of stress suggested it would be worth looking.

The key experiment was quite simple: candies accumulated steadily in a dispenser, but when the dispenser was taken, accumulation stopped. So waiting led to greater rewards, but there was a growing temptation. In some conditions the chimps had toys available - the hypothesis was that toy use would increase during the waiting intervals, suggesting that play was a behavioural strategy for dealing with temptation. In a variation the chimps had no control over the dispenser, because it was out of reach - toy use in that condition was taken as a baseline measure, to be compared to cases where toy use could have been related to resisting temptation.

The results are fairly clear: toy use in the 'toys available' condition was greater (for three out of four of the chimps) when it was up to the individual chimp how long to wait. As the authors conclude:
"This is the first evidence indicating that non-human animals can use a behavioural strategy to reduce their own susceptibility to ongoing temptation."
This is cool stuff. It will be interesting to see how much sophistication in managing impulsivity can be found in other non-human animals when these and other means are made available.

References (besides the 'BPR' tag):

Ainslie, G. (1974) Impulse Control in Pigeons, Journal of the Experimental Analysis of Behavior, 21: 485–489.
Ainslie, G. (2001) Breakdown of Will. Cambridge: Cambridge University Press.

Evans, T.A., Beran, M.J. (2007). Chimpanzees use self-distraction to cope with impulsivity. Biology Letters, 3(6), 599-602. DOI: 10.1098/rsbl.2007.0399


laura l. kilarski said...

that was a great post!

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