Stress reduction through consolation in chimpanzees

Consolation behaviour is interesting in various ways. Why do some individuals spend effort going and doing consoling things to some others? Why, for that matter, don't they sometimes? Why does it sometimes help? When doesn't it?

One promising arena for shedding some light on these questions is observation of the smarter non-human social primates. (There are plenty of open avenues of enquiry here - one of my earlier posts on this blog relates to the effect of social support on perception of geographical slant, which is relevant to the "what does it do" question. I'd like to see some good neuroscience on some of this.) Chimpanzees sometimes enage in consoling behaviour, and it's possible to observe who consoles who, after what, and measure a host of other socially important considerations in detail that would be at least very difficult in humans.

Here's the abstract of the current paper:

Consolation, i.e., postconflict affiliative interaction directed from a third party to the recipient of aggression, is assumed to have a stress-alleviating function. This function, however, has never been demonstrated. This study shows that consolation in chimpanzees reduces behavioral measures of stress in recipients of aggression. Furthermore, consolation was more likely to occur in the absence of reconciliation, i.e., postconflict affiliative interaction between former opponents. Consolation therefore may act as an alternative to reconciliation when the latter does not occur. In the debate about empathy in great apes, evidence for the stress alleviating function of consolation in chimpanzees provides support for the argument that consolation could be critical behavior. Consistent with the argument that relationship quality affects their empathic responses, we found that consolation was more likely between individuals with more valuable relationships. Chimpanzees may thus respond to distressed valuable partners by consoling them, thereby reducing their stress levels, especially in the absence of reconciliation.

Note here that reconcilliation occurs between the conflicting parties, and is not what this study is about.

Here, roughly and leaving out a lot of detail, is what the authors did with a well-established group of chimpanzees varying in size from 26 to 32 members over the course of the study:

1. Observed aggressive conflict, defined as "any interaction involving a bite, hit, brusque rush, trample, chase, or threat in addition to screaming" (p8559). (Obviously a longer list would be needed for research subjects with access to firearms, lawyers, bagpipes and medium sized pieces of iron-mongery.) Conflicts were further analysed to determine who "won", since losing is taken to be more stressful.
2. Measured post-conflict (PC) stress by counting rates of self-grooming and self-scratching, both known to increase under stress. (As before, for subjects who can buy dumb stuff on E-Bay, bang tools together in their shed, etc., a richer coding scheme is required.)
3. Measured consolation behaviours, by counting affiliative interactions, defined as "kiss, embrace, grooming, finger-in-mouth, gentle touch, or play". (Exercise for the reader.)
4. Measured relationship quality between different pairs of chimps, using coding methods developed for use with mother-infant relatioships.

The details I've left out are important - this kind of primatology is tough, and depends on laborious examination and encoding of recordings of interaction and activity, before any analysis can begin. (It involves amounts of crushingly dull drudge work impossible before the invention of the scientific underclass known as the 'graduate student'.) The analysis here also depends on some specific policies dividing up time for coding purposes, and more specifically classifying episodes of consolation as a function of time since conflict.

Subject to the various coding schemes and data collection policies, the authors collected data on 234 pairs of episodes (ones involving post-conflict behaviour and matched controls lacking it) for 22 recipients of aggression, involving 129 distinct pairings of individuals in the original conflict. The sophisticated analysis (detailed in the paper and the supplementary materials) established the main finding: that consolation reduces stress, and that the best predictor of the effect of consolation was relationship quality: it's worth more to be comforted by those who matter to us. The two figures below summarise some of the main results.
























For another article on chimpanzees on this blog (not about consolation) see Chimpanzees use self-distraction to cope with impulsivity.

And for anyone who doesn't know, the picture at the top is Philippe from Achewood (used without permission) . He's got his own blog here.


Fraser, O.N., Stahl, D., Aureli, F. (2008). Stress reduction through consolation in chimpanzees. Proceedings of the National Academy of Sciences, 105(25), 8557-8562. DOI: 10.1073/pnas.0804141105

Chimpanzees use self distraction to cope with impulsivity

This 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