23 October 1998
Lookee, Countee Monkee

Two Columbia University psychologists have taught monkeys to discriminate computer-generated images containing as many as nine objects and to respond to them in ascending order, with a success rate well above what would be predicted by chance.

The work is the strongest evidence so far of numerical ability in non-human primates, said the researchers, Herbert S. Terrace, professor of psychology at Columbia and professor of psychiatry at the New York State Psychiatric Institute, and Elizabeth Brannon, a Columbia graduate student in psychology. Their work appears in the Oct. 23 issue of the journal Science.

The research challenges the prevailing view, which dates to Descartes, that non-human primates cannot think because they cannot use language. It also challenges the views of B.F. Skinner, the noted behaviorist and Prof. Terrace's mentor at Harvard, who held that all examples of animal intelligence were simply conditioned behavior that didn't require cognitive explanations. Prof. Terrace and Ms. Brannon believe that cognitive processes are needed to explain the kind of complex behavior they are studying. They hope to show that human intelligence, like other human attributes, can be traced to animal origins.

"We have ample evidence that animals can think without language," said Prof. Terrace, who heads Columbia's Primate Cognition Laboratory. "In our current and previous research, we have shown that animals solved complex problems without help from external cues."

Added Ms. Brannon, "Though monkeys do not recognize the word 'two' or the symbol '2,' they share with humans the capacity to master simple arithmetic, on at least the level of a two-year-old child. We don't have direct evidence yet, but it seems likely that these monkeys, and other non-human primates, can count."