Ayumu, the amazing chimpanzee

A well-written headline can really catch your eye. Like this one, from an article on National Geographic Online: “Young Chimp Outscores College Students in Memory Test.” I saw that and, of course, had to read the article!

This story is about a study done recently in Japan to test the short-term memory abilities of humans and chimpanzees, and published in the December volume of Current Biology. This test involved 3 chimpanzees (who know the numbers 1 through 9) and 12 human volunteers. The subjects were placed in front of a touch computer screen that displayed 9 numbers in various places around the screen. The task was to touch the numbers in numerical order from 1 to 9. Sounds pretty easy, right? Sure, until you add the last tricky part. Once the number 1 was pressed, the rest of the numbers were covered by white squares. The challenge, therefore, was to remember where each number had been, and still be able to touch them in the proper sequence. Of the subject tested, both the chimps and the humans were about the same in accuracy. But the chimps did it faster.

A second test was done, this time pitting the fastest chimp (named Ayumu) against 9 college students. This time, 5 numbers were flashed briefly on the screen, then covered up with white squares. Again, the subjects had to touch the numbers in order. When the subjects saw the numbers for a long period of time – almost 1 second – both humans and Ayumu performed equally well. However, when the numbers were shown only very briefly – 2 to 4 tenths of a second – Ayumu performed much better than the humans. He was correct approximately 80% of the time, while the human scores dropped by half, to 40%. Ayumu was much better at taking in the whole picture extremely rapidly, and remembering the positions of the numbers, than were his human competitors. I looked at the videos of Ayumu performing the test, and it was pretty incredible. The numbers would flash on the screen and then disappear so quickly that I could hardly even find the first one! But Ayumu consistently touched the numbers in the right order. I was really impressed.

Now, before we start bemoaning the poor intellectual abilities of the humans studied here, one very important caveat must be mentioned. Ayumu is only 5 years old. Chimpanzees can live to be 50 or 60 years old, so he’s still several years away from adulthood. The humans he competed with were in their early 20s, past the age of adolescence. The test uses the ability to handle "eidetic imagery," also known as photographic memory or total recall. This is the ability to remember complex spatial arrangements or sounds with extreme accuracy. Eidetic imagery is known to decrease with age; children perform much better on tests of eidatic imagery than do adults. Perhaps what was really shown in this test was eidatic imagery in chimpanzees? Quite possibly, actually, since Ayumu performed much better on the memory tests than did the older chimps in the study, including Ayumu’s mother, Ai. In fact, Ai actually performed worse on the tests than did the human subjects. So perhaps a better comparison to understand how good Ayumu’s memory is would be to compare him to a human 8-year-old.

The study in question was performed by researcher Tetsuro Matsuzawa of Kyoto University. Dr. Matsuzawa is a leading figure in the field of chimpanzee intelligence. Most of his work is known as the “Ai-project,” which studies the language and number skills of Ai (who is, if you remember, the mother of Ayumu). Ai is 29 years old, and is part of an established colony of chimpanzees in Kyoto, a group that has been studied for intelligence since 1978. That makes this paper one of many from the longest-running study on chimpanzee intelligence in the world.