Robert Deaner of Duke University Medical Center and his colleagues studied male rhesus macaques that received juice rewards while looking at a variety of images of other macaques on a computer screen. The pictures included a neutral target, male monkeys that differed in social standing and the hindquarters of a female monkey, which reveal her sexual receptiveness. By systematically varying the amount of juice offered to the monkeys while changing the pictures they were seeing, the scientists determined how much the animals were willing to give up, or pay, in order to glimpse specific images. The team discovered that monkeys would give up a significant reward if it meant viewing high-ranking individuals or female behinds. But when given the chance to glance at images of low-ranking males, the subjects held out for additional juice.
The findings may help scientists understand the neural wiring that underlies social cognition. "At the moment, it's only a tantalizing possibility, but we believe that similar processes are at work in these monkeys and in people," says study co-author Michael Platt, also at Duke. "After all, the same kinds of social conditions have been important in primate evolution for both nonhuman primates and humans. So, in further experiments, we also want to try to establish in the same way how people attribute value to acquiring visual information about other individuals." The findings will appear in the March issue of Current Biology.