Scientists Rethinking Nature of Animal Memory

August 22, 2003

An elephant never forgets—or does it?

Scientists have long believed that animals do not have so-called episodic memory—the kind that allows humans to remember past events. But recent experiments with scrub jays, chimpanzees, and gorillas have led to rethinking of the nature of memory in animals.

Animal memory researchers first face the challenge of communicating between species. "You can't exactly ask the animals where they were, and what they were doing, when Bambi's mother was shot," says Nicola Clayton, a professor of comparative cognition at University of Cambridge in England and a leading researcher in the field of animal memory.

Over the past six years Clayton has devised a series of ingenious experiments that seem to show that scrub jays can recall past events and use the information to plan for the future.

"We have traditionally regarded animals like machines, or automata, believing that they just have reflexes and habits," says John Pearce, a professor of psychology at Cardiff University in Wales. "Clayton's work is revolutionary because it challenges these ideas and suggests that animals have richer memories than previously thought."

Clayton chose scrub jays because she was fascinated by their food-caching behavior: They stash food to recover later. The jays adapt their caching habits to the perishability of the item, Clayton discovered. In one experiment, Clayton left out worms and peanuts for the jays to store. The birds preferred to retrieve the worms, unless a long period of time had elapsed. Then the birds went for the peanuts—a preference they presumably "remembered" from finding spoiled worms.

Mental Time Travel

One of Clayton's later experiments with the resourceful jays involved observing how they behaved when stashing food in caches that might be robbed by other birds. Jays with experience of such avian robbery were much more cautious about their stashes.

"It is as if the pilferer recognizes that its food could be stolen in the future and makes sure no one sees his cache," Clayton says. "This is the first time we have seen evidence that an animal other than a human recalled the social context of an event and adjusted its future behavior."

Psychologists say that episodic memory mediates the ability to remember—or to engage in a form of "mental time travel." The question is whether that ability is uniquely human.

"There are many beautiful examples of complex behavior that occur without higher thought or consciousness," cautions Endel Tulving, a cognitive psychologist at the Rotman Research Institute of Baycrest Center for Geriatric Care in Toronto. In his book "Elements of Episodic Memory," Tulving wrote that animals can adjust, adapt, and learn, but they cannot "travel back into the past in their own minds." But he enjoys the fact that scientists are challenging his ideas.

Neither Clayton nor Pearce are completely convinced yet that the jays have episodic memory and can replay past events in their minds like humans do. But the jay experiments have inspired similar studies in other species.

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