A few months ago I moved to Reno, Nevada. Although I haven’t been to a casino yet myself, living in a so-called ‘casino town’ makes you acutely aware of the effects of gambling on people. But why do people gamble to begin with? Surely if we know that the odds are stacked against us, we wouldn’t take a risk with a large sum of money? Well, everyone knows that this clearly is not the case. According to the State of Nevada Gaming Control Board, casinos in Nevada made over one billion dollars in just the month of December alone (2013). In Macau, the largest gaming zone in the world, the casino revenue was over $33 billion in 2011.

Reasons humans lose so much money gambling include the fact that people rely on emotions, irrational thoughts and may have a misunderstanding of odds rather than on the probabilities of coming out ‘on top’ over a longer period of time. If there’s a chance of winning a lot in the short term, humans are likely to be swayed even if they are unlikely to win.

One way of testing people’s choices when the immediate and long-term outcomes of a choice are put into conflict is the Iowa Gambling Task (IGT), so named because it was invented by researchers at the University of Iowa. In this task, participants are presented with 4 decks of cards to choose a card from, that either results in them winning a particular amount of money, or losing some money. Two of the decks result in net losses, but include some cards that give higher payouts, whereas the other two decks don’t have high payouts, but are more consistent over time and lead to higher net gains. I had a go at a demo version of this game, and I have to admit I was tempted by the larger sums and ended up coming out in debt, perhaps a sign that I’m not ready for the Reno casinos quite yet.

When people are tested on this task, there is a mix in the strategy that people employ: some go for the decks that yield the greatest reward in the long-term, whereas others (like myself, apparently) are too tempted by the short-term gains. However, for the people that choose the ‘sensible’ option, is it because they are aiming to gain high rewards overall, or because they are avoiding the greater variation in rewards that comes with choosing the other deck?

In order to better understand this, a recent study compared what we do to what other primates do when tested on the same task. As an analogue to the IGT, the researchers developed the ‘Primate Gambling Task’ (PGT) which basically simplifies the IGT to a pair of decks rather than 4, uses food rather than money, and does not have negative rewards (as it’s too hard to remove food that you’ve already given to an animal).

Using capuchin monkeys and chimpanzees, the researchers compared their performance on this test to that of humans. They used a modified IGT task for the humans too, to make sure that it was similar to the non-human primates, and the humans performed similarly on it as to traditional IGT tasks.

The researchers found that chimps, capuchins and humans all chose the deck that maximised rewards long-term and had the smallest amount of variance in rewards. To see whether the individuals were trying to maximise their rewards, or just avoid the condition that had more variance, the researchers then tested all the primates on two more conditions to disentangle what might be going on.

For the capuchins, chimps and the humans, all three species were more likely to choose the deck that was rewarding in the long term when it both maximised payoff and gave less variable rewards. However, some chimps favoured maximising payoff, whereas other chimps really liked decks which gave less variable rewards. This is similar to what has been found previously with humans. This contrasts with the capuchin monkeys, who always preferred to maximise their rewards, even when the rewards were variable.

Why is it that the capuchins were safer gamblers than the chimps or humans? The authors suggest that this may have been due to capuchins individuals generally being more similar to each other than chimpanzees are to other chimpanzees. Furthermore, how these animals forage for food in the wild may affect how they make decisions and weigh pros and cons of choices.



Reno: Patrick Nouhailler

cards: Kevin Shine

Capuchin monkey: taken from Proctor et al. 2014

chimpanzee: Nils Rinaldi



Proctor, D., Williamson, R. A., Latzman, R. D., de Waal, F. B., & Brosnan, S. F. (2014). Gambling primates: reactions to a modified Iowa Gambling Task in humans, chimpanzees and capuchin monkeys. Animal cognition, DOI 10.1007/s10071-014-0730-7