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December 03, 2007

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Humans lose to chimps in number memory game

Dec. 3, 2007
Courtesy Current Biology
and World Science staff

Young chim­panzees have an “ex­tra­or­di­nary” abil­ity to re­mem­ber nu­mer­als that’s su­pe­ri­or to that of hu­man adults, re­search­ers say based on a new stu­dy.

“There are still many peo­ple, in­clud­ing many bi­ol­o­gists, who be­lieve that hu­mans are su­pe­ri­or to chim­panzees in all cog­ni­tive func­tions,” said Tet­suro Mat­suzawa of Kyo­to Un­ivers­ity in Ja­pan. “No one can im­ag­ine that chim­panzees—young chim­panzees at the age of five—have a bet­ter per­for­mance in a mem­o­ry task than hu­mans.”

(Max Planck Institute for Evolutionary Anthropology/Esther Herrmann)
But the stu­dy, he said, found “that young chim­panzees have an ex­tra­or­di­nary work­ing mem­o­ry ca­pa­bil­ity for nu­mer­i­cal recollection—bet­ter than that of hu­man adults” tested the same way. The find­ings ap­pear in the Dec. 4 is­sue of Cur­rent Bi­ol­o­gy, a re­search jour­nal.

Mat­suzawa and col­leagues tested three pairs of moth­er and in­fant chimps, all of which had al­ready learn­ed the in­creas­ing or­der of Ar­a­bic nu­mer­als from 1 to 9, against un­ivers­ity stu­dents. One moth­er, named Ai, was the first chimp to have learn­ed to use Ar­a­bic nu­mer­als to la­bel sets of ob­jects with the cor­rect num­ber.

In the new test, chimps and hu­mans were briefly shown var­i­ous nu­mer­als from 1 to 9 on a com­put­er screen. The num­bers were then re­placed with blank squares. The test sub­ject had to re­mem­ber which num­ber had ap­peared where, and tou­ch the squares in the right or­der.

Young chimps could grasp many nu­mer­als at a glance, with no de­crease in per­for­mance even when num­bers were kept on the screen for a shorter time, the re­search­ers found. In gen­er­al, the three young chimps did bet­ter than their moth­ers. Adult hu­mans, too, were slower than all three young chim­panzees, and per­formed worse when the num­bers were shown for shorter amounts of time, the team found.

Mat­suzawa said the newfound abil­ity of chimps, our clos­est ev­o­lu­tion­ary rel­a­tives, is rem­i­nis­cent of “ei­de­tic im­agery,” a spe­cial ca­pa­city to keep a pre­cise men­tal im­age of a com­plex scene or pat­tern. Such a “pho­tographic mem­o­ry” is known to ex­ist in some nor­mal hu­man chil­dren, and typ­ic­ally de­clines with age, he added. Young chimps’ new­found abil­ity to top hu­mans in the nu­mer­i­cal mem­o­ry task is “just a part of the very flex­i­ble in­tel­li­gence of young chim­panzees,” said the re­search­ers in an an­nounce­ment of their find­ings.

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Young chimpanzees have an “extraordinary” ability to remember numerals that’s superior to that of human adults, researchers say based on a new study. “There are still many people, including many biologists, who believe that humans are superior to chimpanzees in all cognitive functions,” said Tetsuro Matsuzawa of Kyoto University in Japan. “No one can imagine that chimpanzees—young chimpanzees at the age of five—have a better performance in a memory task than humans.” But the study, he said, found “that young chimpanzees have an extraordinary working memory capability for numerical recollection—better than that of human adults” tested the same way. The findings appear in the Dec. 4 issue of Current Biology, a research journal. Matsuzawa and colleagues tested three pairs of mother and infant chimps, all of which had already learned the increasing order of Arabic numerals from 1 to 9, against university students. One mother, named Ai, was the first chimp to have learned to use Arabic numerals to label sets of real objects with the correct number. In the new test, chimps and humans were briefly shown various numerals from 1 to 9 on a computer screen. The numbers were then replaced with blank squares. The test subject had to remember which number had appeared where, and touch the squares in the right order. Young chimps could grasp many numerals at a glance, with no decrease in performance even when numbers were kept on the screen for a shorter time, the researchers found. In general, the three young chimps did better than their mothers. Adult humans, too, were slower than all three young chimpanzees, and performed worse when the numbers were shown for shorter amounts of time, the team found. Matsuzawa said the ability of chimps, our closest evolutionary relatives, is reminiscent of “eidetic imagery,” a special capacity to keep an accurate image of a complex scene or pattern. Such a “photographic memory” is known to exist in some normal human children, and typically declines with age, he added. Young chimps’ newfound ability to top humans in the numerical memory task is “just a part of the very flexible intelligence of young chimpanzees,” said the researchers in an announcement of their findings.