Wednesday, February 9, 2011

Researchers examine how primates and humans cooperate to gain rewards

Humans often work together toward a common goal. Now, Georgia State University researchers and their colleagues have found that humans aren’t the only ones to work together for a bigger payoff.

They found that in primates such as chimpanzees and capuchin monkeys, the animals also cooperated in a game to test whether two individuals would aim for higher rewards at a higher risk.

The results were published online this week in the Proceedings of the National Academy of Science.

As part of research investigating the development of economic decision making in humans, Sarah Brosnan, an assistant professor of psychology and neuroscience at Georgia State, and her partners, tested primates and humans by having them play the “Assurance” game.

The game involves two individuals working together to earn a high reward at a greater risk, called the “payoff dominant outcome,” or going for a lower risk, lower payoff reward, called the “risk dominant outcome.” In both cases, the chimpanzees and monkeys received fruit, while humans received money.

In this version of the game, neither humans nor other primates were given instructions, but learned the payoff structure as they played, leveling the playing field among the species.

The primates performed about the same as humans, but humans didn’t perform as well in this game as expected compared to results in the more typical game format, which uses instructions, Brosnan said. In addition, the results yielded other differences in how primates and humans perform in the game.

“Humans and capuchins may not make decisions in exactly the same way,” she said. “But capuchins seem to have the capacity to reach similar decisions as do humans. Bear in mind that only a fifth of the humans found the payoff dominant outcome.”

The researcher also found differences between chimpanzees, some of whom had been reared in a cognitively enriched environment from an early age and some of whom had been raised typically, Brosnan said. The former chimpanzees did far better than did the latter.

“This implies that rearing is important, which nobody disputes when it comes to humans, but as these results indicate is clearly the case for chimpanzees as well,” she said.

Brosnan and her colleagues are interested in the study of decision making and how it evolved in humans to better understand how humans developed complex economic systems, including such things as specialization and trade.

“These decisions about who to interact with and who to cooperate with are essential to human life,” she said. “Even in non-Western societies that are not as well tied into the global economic system, people are still making decisions about how to acquire and distribute resources in ways we don’t see in other species.

“Other species show evidence of some degree of these behaviors, but none of them have taken the extra step and gone on to specialization and then trade, which are one of the foundations of human economics,” Brosnan explained.

Researchers used the non-human primate facilities of Georgia State’s Language Research Center, as well as the Michale E. Keeling Center for Comparative Medicine and Research at the University of Texas’ M.D. Anderson Cancer Center in Bastrop, Texas. Human research was done at the Economic Science Institute of Chapman University in Orange, Calif.

The team included Brosnan, Audrery Parrish, Michael J. Beran, Timothy Flemming, Lisa Heimbauer and Catherine F. Talbot of GSU; Susan P. Lambeth and Steven J. Schapiro of the M.D. Anderson Cancer Center; and Bart J. Wilson of the Economic Science Institute of Chapman University.

 The study is available online at www.pnas.org under the “Early Edition” section.

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