Monkeys Can Handle Statistics

You may believe that monkeys are capable of only cheap tricks and imitation, but a new research on rhesus monkeys revealed they can handle statistics...

Many students cannot...

The monkeys could accurately determine which of two behaviors is more likely to reward them by summing together a series of probabilistic factors. Their ability was correlated with the firing rate of the brain's individual neurons.

The team made by Tianming Yang and Michael Shadlen at the Howard Hughes Medical Institute and the University of Washington in Seattle, US, worked with two rhesus macaques by presenting them a series of abstract shapes on a video screen.

Each shape was linked to a different probability that a drink reward would be connected to a red instead of a green target. In each test, the monkey was presented a sequence of 4 of 10 possible shapes and it had to choose which target to look at. The probability that the red target would offer the reward was the sum of the probabilities for each of the four shapes; otherwise, the green target yielded the drink.

It took several weeks of training on thousands of trials daily but the monkeys were able to make their choices depending on the probabilities of the shapes, choosing the right target in over 75% of the cases. It was the first time when it was proved that monkeys are able to use probabilistic factors.

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

Brain electrodes recorded the activity of 64 neurons in the lateral intraparietal area, a side of the brain involved in attention and visual processing. The neurons reacted to the first shape by firing at a rate matching the probability linked to that shape.

"We're seeing neurons that are making computations. In particular, the neurons appeared to be computing the log likelihood ratio of red versus green rewards - exactly the sort of computation a statistician might do. We're exposing the basic elements, the fundamental biology of higher cognition," said Shadlen.

Moreover, the team wants to get more details on the decision-making process.