See, Monkeys Are Like People — When It Comes to Computing Payoffs

June 13, 2007

Monkeys could feel right at home in a casino. They appear to be capable of probabilistic reasoning—especially if a correct calculation leads to a reward, according to study published online in Nature.

Tianming Yang and Michael Shadlen, both from the University of Washington in Seattle, tested the reasoning of two rhesus monkeys. They showed the animals a series of abstract shapes on a video screen. Each shape corresponded to a different probability that a drink reward would be associated with a red instead of a green target. In each trial, a monkey saw a sequence of four shapes, then had to choose which target to look at. The probability that the red target would give the reward was the sum of the probabilities for each of the given shapes. Otherwise, the green target yielded the drink.

After weeks of training and thousands of trials (no geniuses here), both monkeys learned enough about the associated probabilities to choose the correct target more than 75 percent of the time.

"When we started this, we thought it was a high-risk project," Shadlen told New Scientist. "When we had monkeys doing it, I was pretty shocked."

By recording signals from a particular area of a monkey brain's parietal cortex, the researchers observed changes in the firing of neurons, which suggested a kind of addition and subtraction was taking place. It seemed as if the animals were trying to evaluate the alternatives.

The authors suggest that their research demonstrates that monkeys have an elemental capacity for probabilistic inference, just as people do when they make choices based on calculations of anticipated payoffs.

Source: Nature, June 3, 2007; New Scientist, June 3, 2007