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March 14, 2002


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HARVARD GAZETTE ARCHIVES

Marc Hauser
Experiments done by Marc Hauser convince him that animals have interesting thoughts, particularly chimps and monkeys, who lead relatively rich social lives. (Staff photo by Stephanie Mitchell)

Scientists think that animals think:

But what exactly do they think about?

By William J. Cromie
Gazette Staff

Do animals think?

"Of course they do," answers Marc Hauser, a Harvard professor of psychology. "How could they not think and manage to survive in the world?"

Hauser has been studying animal cognition since 1980, when a female spider monkey reached through the bars of her cage at Florida's Monkey Jungle and gave him a hug. He was 19 years old at the time. "She looked into my eyes and cooed several times," he remembers. "The experience got me to thinking about what animals are thinking and how to find out."

He now believes that animals conceive the world in ways similar to humans, especially species like chimpanzees who live a rich social life. His field and laboratory experiments suggest that humans got their mechanisms for perception from animals. "Those mechanisms came free, courtesy of evolution," he says.

Hauser and his colleagues are trying to determine what sorts of thinking processes are unique to humans and what processes we share with animals. The one that comes immediately to mind is language.

"Animals have interesting thoughts, but the only way they can convey them is by grunts, shrieks, and other vocalizations, and by gestures," Hauser points out. "When humans evolved speech, they liberated the kinds of thoughts nonhumans have. Feedback between language and thinking then boosted human self-awareness and other cognitive functions."

Can your pet think?

Most pet owners fervently believe that Fido or Fluffy has superior intelligence. One of the markers of intelligence is self-awareness, so here is a quick test to see if the animal has that ability.

Position a mirror by your pet’s food dish, so it can see its face and head. Whenever you feed it pat the dog, cat, or whatever on the head. Repeat this routine for three to four days.

When you’re ready, put some odorless light or dark powder in your hand and pat it onto your pet’s head. You can use baking soda or carbon black. Make sure you create a clearly visible spot on its head.

Watch the animal closely to see if it stares at itself, or tries to rub the spot. If it does, congratulations, your pet has some sense of self.

For more pet intelligence tests, consult “Wild Minds” by Marc Hauser (Henry Holt, 2000).

Monkeys get the rhythms

Clever experiments with monkeys and human infants show that they share thinking processes once thought to be in the minds of humans alone. Babies only 3-4 days old can tell the difference between two languages such as Dutch and Japanese. When the infants hear someone saying sentences in Dutch, they express their interest by sucking rapidly on the nipples of pacifiers. After a while they get bored with the Dutch talk and stop sucking enthusiastically. If someone then starts speaking Japanese, they will show increased interest by upping their sucking rate.

The babies don't know what the speakers are talking about, of course, but they can discriminate between languages by the change in rhythms. They don't respond to languages with similar rhythms, such as Dutch and English or French and Spanish. Also, if you play the same sentences backward, the infants fail to react. "One explanation for this behavior is that they intuitively know that no human vocal tract can produce such sounds," Hauser explains.

If this is true, monkeys should not be able to make the same distinctions because they don't know what rhythms and sounds human vocal tracts can produce. But cotton-top tamarin monkeys easily distinguish between Dutch and Japanese. They look at a speaker broadcasting sentences of Dutch, look away when they're bored, then look back when someone starts speaking Japanese. And they cannot make that distinction when the sentences are spoken backward.

"The monkeys have the same perceptual abilities as us," Hauser concludes. "That means such perception did not evolve with human speech; it existed before humans and speech evolved."

Babies do statistics

One big mystery about human cognition is how babies decide when one word ends and another begins when they listen to an adult's stream of speech. Experiments done in 1996 revealed that kids as young as 8 months are capable of performing a kind of statistical analysis that seems pretty amazing.

The babies listen to a continuous stream of consonants and vowels, such as "dapikutilado...." Some combinations always cluster together, like "da-pi-ku," while others do not. If infants are aware of statistically familiar clusters, they show little interest when they hear them. But when they hear something like "da-ku-pi," they know something is unfamiliar. They look toward the sounds of unfamiliar triplets longer than they look in the direction of those that are relatively familiar.

The youngsters don't know it, but that's how they will get the hang of separating words in a stream of speech. Linguists call this "computing transitional probabilities." It sounds too complicated for an 8-month-old, much less for a monkey. However, Hauser and his two collaborators, Elissa Newport and Richard Aslin, showed that cotton-top tamarins can do the same thing.

Perceptual and at least some computation mechanisms, therefore, lived in the brains of animals long before humans came along, even ancient humans who didn't do much more than grunt and bellow. "Some people wouldn't call these abilities 'thinking,'" Hauser admits. "That's fine with me. But it begs the question, 'What do you mean by thinking?'"

How high can animals count

Additional tests by Hauser and other researchers reveal that monkeys can count up to four. The human ability to count to higher numbers apparently came only after we evolved language and developed words to describe quantities like 25 and 1,000.

Some human cultures still don't use large numbers. The Hadza people, hunter-gatherers in Tanzania, for example, have words only for "one," "two," and "three"; anything more is "many." They are aware that a picture with 30 dots displays a larger number than one with 20 dots (as are monkeys), but they have no words for the precise numbers of dots.

The bottleneck between human and nonhuman thinking involves not just words, but the ability to recombine words in an endless variety of new meanings. That appears to be a unique human capability. Chimpanzees have a rich social and conceptual life, Hauser maintains, but they can't discuss it with each other.

The next step in determining how much thinking ability humans share with other animals will involve scanning the brains of both while they do the same cognitive tasks. Harvard psychologists have already begun to do this in a collaboration with researchers from the University of Massachusetts Medical School in Worcester and the Max Planck Institute in Germany. Monkeys may exhibit the same kind of intellectual behavior as humans, but do they both use the same areas of the brain?

"We have a great deal of data that show what areas of the brain are activated when humans respond to various situations," Hauser points out. "Now we will determine if monkeys and other animals utilize the same brain circuits."

So far, the monkeys are adapting well to experiments at the University of Massachusetts. They move into harnesses in brain scanning instruments, such as MRI machines, without difficulty. Measurements of their stress levels show that after five days of training, marmoset monkeys feel as comfortable as they do in their home cages with their own social group.

For some people, such research will not provide a satisfactory answer to the question: Do animals really think? These people define thinking as having a sense of self, beliefs that go beyond raw perceptions, emotions such as empathy, and the ability to imagine a situation remote in time and place and predict an outcome.

"Those capabilities cannot be illuminated by brain scanning," Hauser admits. "But experiments using other techniques are beginning to shed light on what kinds of perceptual and computation skills animals bring to analyzing the world, and in what ways these skills are different from our own."

I think, therefore I am. - Descartes

For more information about nonhuman thinking, see Hauser's book "Wild Minds," (Henry Holt, 2000). Hauser will debate distinguished linguist Noam Chomsky on March 30 at Harvard at a conference sponsored by the Language Evolution Society.









Copyright 2002 by the President and Fellows of Harvard College