In the test with real food, the monkeys chose one piece of A over two pieces of B; and would choose one piece of B over two pieces of C. And the effect continued so that they might chose one piece of A, their favourite food, over four pieces of less tempting C. They were then offered a similar test, but with the trays loaded with tokens representing the different foods. The monkeys responded in the same way – for example choosing one A token (redeemable for a piece of A food), over two B tokens. This shows that the same reasoning is used for both tasks, says Addessi, who presents the results in the journal PLoS ONE. But the monkeys behaved differently with real food and with tokens. This was apparent when the monkeys had to decide whether a large amount of a less-tasty food would be better than a single piece of their favourite food. In both tests there came a point when lots of B, or B tokens, would be chosen over a single piece of A, or an A token.
With real food, this threshold was around three pieces of B. But for the token test much more of the less-favoured food needed to be offered before the monkey would choose that option. It's unclear why this should be the case, says Addessi. “They are able to reason with tokens as with real food, but they find it more difficult to reason with tokens,” she says. This behaviour is similar to that of a small child. An alternative explanation might be that tokens are an abstract concept. The monkeys become less good at comparing two abstract sets of food – in a similar way to how many people spend more freely with a credit card than with cold, hard cash.
June 24, 2008
Original web page at Nature