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Ape Has Memory Span Comparable to Humans'

April 4, 2000

Ai's skill at this game shows she understands numbers, including the zero concept. (Jiji Press)

Scientists at Kyoto University's Primate Research Institute have discovered that a 23-year-old female chimpanzee named Ai, who lives at the center, has mnemonic capabilities on a par with those of human adults. The experiments that established the chimp's memory span were conducted by Professor Tetsuro Matsuzawa and research fellow Nobuyuki Kawai of the institute, which is located in the city of Inuyama, Aichi Prefecture. Ai has displayed remarkable mental powers in many previous experiments, and the latest round of tests confirmed her intelligence yet again. The researchers published their findings in the January 6, 2000, issue of the English-language scientific magazine Nature.

Understanding the Concept of Zero
In one experiment, several single-digit numbers were displayed simultaneously on a computer screen, and Ai was asked to choose the smallest number. When the figures 0, 1, 4, 6, and 9 appeared, for example, Ai touched the 0. The other four numbers were then covered with squares, and Ai was asked to touch these squares in the order of the hidden numbers' values, from smallest to largest. She was able to do this highly accurately.

The ability to commit figures, letters, or other bits of information to memory instantaneously is known as short-term memory. Until now, this ability was thought to be unique to humans: Adult human beings are said to be able to hold anywhere from 5 to 9 items in short-term memory, the average being 7. But Ai was found to be able to retain at least 5 numbers, placing her mnemonic capabilities within the human range.In another experiment, researchers had the chimp count white dots on a computer screen and indicate the numeral that corresponded to the number of dots. When there were four dots on the screen, Ai selected the number 4. When there were five dots, she selected the number 5. And when there were no dots on the screen, Ai correctly selected 0.

The experiments proved that Ai understands the concept of zero both in the ordinal sense--as the number preceding one in the sequence of single-digit numerals--and in the quantitative sense, as the number representing nullity. Matsuzawa says that Ai is the first nonhuman animal to be shown to understand the sequential significance of numbers and the concept of zero. The experiments have attracted the keen interest of many researchers who consider the findings extremely important in gaining an understanding of human cognitive processes.

Can Chimps Pass Knowledge on to Future Generations?
Ai was born in Africa and is believed to have been born around October 1976. She was brought to the research center at the age of one, where, at age two, she began learning symbols by using a computer. So far she has learned over 100 characters, including kanji characters, English alphabet letters, and Arabic numerals. She understands the concept of money and has learned to use a 100-yen (0.91 U.S. dollars at 110 yen to the dollar) coin to purchase an apple from a fake vending machine rigged up by researchers. Ai has shown the ability to look at a facial photo upside-down and recognize, more quickly than a human subject can, who is in the photo.

Ai is now pregnant; her baby is due in April 2000. As a member of a second generation of lab chimps, the baby is eagerly awaited by scientists, who are looking forward to doing the world's first research to determine whether chimpanzees can transmit to their offspring the abstract knowledge they have gained in the lab.

Trends in JapanCopyright (c) 2000 Japan Information Network. Edited by Japan Echo Inc. based on domestic Japanese news sources. Articles presented here are offered for reference purposes and do not necessarily represent the policy or views of the Japanese Government.