Chimp Champ: Ape aces memory test, outscores people

OK, humanity: time to pull up our socks. In a test of rapid number recollection, college students were resoundingly outperformed by a young chimpanzee.

FLYING FINGER. A chimp learned the sequence of numbers 1 to 9 and then wowed researchers with skill at a memory test. AP/Wide World

FLYING FINGER. A chimp learned the sequence of numbers 1 to 9 and then wowed researchers with skill at a memory test. To see a video clip of Ayumu demonstrating his memory skills, click here or on the image above.
Image: AP/Wide World; Video courtesy of Current Biology.

At Kyoto University in Japan, students and chimps saw an array of five of the numerals 1 through 9 flash onto a computer screen for just 650 milliseconds. When the numerals simultaneously turned into white squares, the subjects had to touch the squares in numerical order. The students managed to choose the squares in the correct order around 80 percent of the time, as did Ayumu, a young chimp, says Kyoto’s Tetsuro Matsuzawa.

The researchers then shortened the viewing time to 430 ms and finally to just 210 ms, which isn’t even enough time for a person’s eye to scan across a screen. For the briefest exposures, the students got the sequence right only 40 percent of the time, but Ayumu still managed nearly 80 percent accuracy.

“The memory aspect is really surprising,” says Elizabeth Brannon of Duke University in Durham, N.C.

Matsuzawa suggests that Ayumu’s prowess comes from something akin to photographic memory in humans. The power to retain extreme detail from a quick glimpse shows up occasionally in young children but fades with age. Youth seems to be an advantage for chimps too, Matsuzawa and Sana Inoue say in the Dec. 4 Current Biology.

The researchers worked with three pairs of mother-child chimps. Ayumu’s mother, Ai, had starred in earlier research papers when she learned to associate sets of objects with the appropriate numerals.

Researchers trained all the chimps to tap numerals from 1 to 9 in order, then switched to tests in which numerals popped up briefly on the screen and then turned into white squares. Because the exposure times are so brief, the test challenges perception as well as memory, says comparative psychologist Herbert Roitblat of Ventura, Calif.

On average, the three young chimps outperformed their mothers, the researchers say. Even Ai, despite her skill in using numbers as symbols, proved less accurate than her son. Brannon says she’ll be interested to see whether Ayumu loses his edge as he ages.

“The test says absolutely zero about chimpanzees and numerosity,” comments Brannon, who studies number skills in non-human primates. She predicts that the test could have substituted other shapes for the numerals in the test. “It’s really about memory,” she says.

“It is a terrific animal-human comparison of the cognitive ability to remember the locations of an ordered sequence,” says Anthony A. Wright of the University of Texas Health Science Center in Houston.

“Chimpanzees may have a perceptual advantage that is slowed down in humans, whose knowledge of counting may interfere,” says Sally Boysen of the Ohio State University in Columbus.

However, Matsuzawa’s results don’t mean that people will always lose to chimps, Brannon says. Ayumu might be an exceptional chimp, and some exceptional people, including children, might be able to keep up with him.

Overall, the scores for people and chimps greatly overlapped. To Brannon, this convergence suggests a basic likeness in the two species’ memory mechanisms. “I would argue that this is showing a major qualitative similarity rather than a major difference,” she says.

As to why researchers pit humans against other species, Roitblat says comparisons with close and distant relatives offer a way to infer the evolutionary path of human capacities. “Are we intelligent because we have language or do we have language because we are intelligent?” Roitblat asks.

Susan Milius

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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