Shumaker Finds Orangutans Can Discriminate Quantity

Posted: December 10, 2001 at 1:00 am, Last Updated: November 30, -0001 at 12:00 am

By Robin Herron

In groundbreaking research conducted by Robert Shumaker, director of cognitive behavioral research at the Krasnow Institute for Advanced Study, orangutans have shown that they can judge differences in quantity. Shumaker, who is also a biologist at the National Zoo, conducted the research with two orangutans at the zoo, a male named Azy and his sister Indah. The research findings are published in the December issue of the Journal of Comparative Psychology.

In the experiments, Shumaker presented the subject ape with two quantities of grapes ranging from one to six. The ape was allowed to choose one of the quantities, which was then removed, and the ape received the remaining grapes. The reversed reinforcement contingency meant that the only way to optimize performance was by choosing the smaller quantity first at all times.

Both orangutans demonstrated the ability to differentiate all quantities ranging from one to six, and solved the reinforcement contingency. Azy reached a score of 100 percent accuracy, and Indah reached a high score of 95 percent.

“The results suggest a cognitive difference between chimpanzees and orangutans,” Shumaker says. “Chimpanzees, who live in a complex and competitive social environment, benefit from being impulsive in their decisions about food. Orangutans, who are much more solitary than chimpanzees and rarely have direct competition for their food, are able to be more contemplative about their decisions.”

“Rob’s work is helping to shape our understanding of how human higher cognition evolved,” says James Olds, institute director. “The institute’s commitment to his research on orangutan learning will likely expand further in the future.”

Shumaker will discuss his research at today’s Krasnow Monday Seminar, held at the institute at 4 p.m. All are welcome to attend.

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