Researchers from Kyoto University’s Primate Research Institute report that a young chimp can out-perform university students on a working memory task. (Cognitive psychologists use the term working memory to refer to the temporary storage and manipulation of information.)
The researchers developed a memory test called the limited-hold memory task in order to compare the working memory of their chimps with that of humans. In the task, numbers are displayed on a screen for fractions of a second, before being covered by white squares. The subject is then required to touch the squares in correct numerical order.
In this test, the human subjects – 9 university students – performed progressively worse, as the period of time for which the numerals are displayed decreases from 600 to 210 milliseconds. This is to be expected, as 210 ms is about the frequency of saccadic eye movements; humans cannot scan the screen quickly enough to see all the numbers being displayed.
This was also observed in Ai, a chimp who the researchers had trained, more than 20 years ago, to use numerals to indicate the number of objects beign displayed. Another chimp, however, a 7-year-old named Ayumu, performed consistently well throught the task. The film clip below shows Ayumu performing the task; you can do the task at the same time while watching it, and compare your performance with his.
This study shows that chimps can memorize at a glance the numerals presented on the screen, and that they can do so just as well – and even better – than humans can. Note that the superior performance came from a young chimp, and that the performance of older chimps on the same task was more similar to that of humans.
Now, the Japanese group woud like to determine how long the chimps’ memory trace of the numerals lasts. In one trial, Ayumu was distracted from the task for about 10 seconds, and yet could still recall the numbers on the screen in the correct order.
The researchers believe that their subjects – both chimp and human – used edietic imagery in the task at hand. Also known as photographic memory, this involves generating an accurate mental “snapshot” of a complex scene – in this case, the positions of numerals on a screen – and retaining it for long enough for recall.
They further suggest that humans lost their ability for accurate eidetic imagery during the course of their evolution, such that the brain could accomodate other complex processes such as language.
Inoue, S. & Matsuzawa, T. (2007). Working memory of numerals in chimpanzees. Curr. Biol. 17: R1004-R1005. [Abstract]