Hanging from the Language Tree

In a famous experiment over 30 years ago, psychology professor Herb Terrace hoped to prove that chimpanzees could acquire speech. Today, as director of the Primate Cognition Laboratory at Columbia, he’s searching for the missing link to cognition.

by Cindy Rodríguez Published Fall 2009
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A popular theory among psychologists who work with nonhuman primates is that apes and monkeys form thoughts by conjuring images in their minds without the need to attach words to concepts. Using this thought process, Terrace says, monkeys can think in abstract terms, and can even understand the limitations of their knowledge and strategize ways to improve what they know, what psychologists call metacognition.

Metacognition studies on animals are still in their infancy. The first paper on the topic was published in 1997 by J. David Smith, a psychologist at the State University of New York at Buffalo. The test subjects were dolphins.

“Twenty years ago a lot of people would have said it was impossible to answer the question, ‘Can monkeys think about their thinking?’ ” says Hampton, who also does cognitive research on rhesus macaques. “But now we’re fairly confident that monkeys regulate their own thinking and can comment on it.”

High-Stakes Testing, Monkey-Style

These days, Terrace is in the midst of perfecting a metacognition test he believes will provide further evidence that monkeys can use the highest level of problem-solving skills, regulating their thinking in a manner that suggests to some psychologists that they have a reflective conscious.

In this test, monkeys are shown five to nine photographs, which they have to memorize. Then, several photographs appear on a screen, with some distracter photographs. The monkey has to decide which photographs were shown in the original bunch by tapping on a “yes” or “no” icon. Next comes the tricky part: they have to decide how well they think they did and place bets on their own performance. It forces them to think: did I do poorly or ace it?

They can bet “high,” which will give them more banana pellets if they are right, but if they’re wrong, they will see the tokens on the screen disappear. If they bet “low,” they don’t lose much, but all they stand to win is a single banana pellet. So they need to think smart and be discerning if they want to win a jackpot of banana pellets.

If the monkeys seem to be getting bored of the tests, Terrace ups the ante by replacing the banana pellets with M&M’s. “It’s as if now you’re playing poker for fifty dollars instead of ten dollars,” he says.

Monkeys hate to lose, especially when their reward is a snack. On occasions when they lose any chance of getting a banana pellet, they act eerily like someone at a casino who has lost a huge amount of money. They stare at the computer monitor and shriek in disbelief as they watch the tokens disappear from the screen. They frown. They fall backward. They cover their faces with their arms. The losses seem to make them strive to do better next time, says Terrace.

Ebbinghaus, named for the German psychologist Hermann Ebbinghaus, is the new star of the bunch. On a new test given recently, he was able to assess whether he did poorly, OK, or very well. He chose high risk and was accurate 77 percent of the time.

The results have huge significance. “This shows us that he’s choosing discriminatively,” says Gin Morgan, one of Terrace’s graduate students who helped devise and run the test. “It means that he not only understands the task but, more important, that he can reflect on his performance and decide whether or not it was correct.”

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