From Goldman and Bisanz (in press). Toward a Functional Analysis of Scientific Genres: Implications for Understanding and Learning Processes. In J. Otero, J. A. León, & A. C. Graesser (Eds.), The psychology of science text comprehension. Mahwah, NJ: Erlbaum.  

Handout 1/16/02  Psych 303

Table 2 A Brief Illustration of the Research Report Genre

Cognition: Numerical memory span in a chimpanzee

NOBUYUKI­KAWAI AND TETSURO­MATSUZAWA

Primate Research Institute, Kyoto University, Inuyama, Aichi 484-8506, Japan

(Introduction)

A female chimpanzee called Ai has learned to use Arabic numerals to represent numbers 1. She can count from zero to nine items, which she demonstrates by touching the appropriate number on a touch-sensitive monitor 2, 3, and she can order the numbers from zero to nine in sequence 4-6. Here we investigate Ai's memory span by testing her skill in these numerical tasks, and find that she can remember the correct sequence of any five numbers selected from the range zero to nine.

            Humans can easily memorize strings of codes such as phone numbers and postcodes if they consist of up to seven items, but above this number they find it much harder. This 'magic number 7' effect, as it is known in human information processing7, represents a limit for the number of items that can be handled simultaneously by the brain.

(Method)        

            To determine the equivalent 'magic number' in a chimpanzee, we presented our subject with a set of numbers on a screen, say 1, 3, 4, 6 and 9. She had already displayed close to perfect accuracy when required to choose numerals in ascending order, but for this experiment all the remaining numbers were masked by white squares once she had selected the first number. This meant that, in order to be correct in a trial, she had to memorize all the numbers, as well as their respective positions, before making the first response. Chance levels with three, four and five items were 50, 13 and 6%, respectively.

(Results)

            Ai scored more than 90% with four items and about 65% with five items, significantly above chance in each case. In normal background trials, response latency was longest for the first numeral and much shorter for all the others, indicating that Ai inspected the numbers and their locations and planned her actions before making her first choice. In masking trials, response latency increased only for the choice directly after the onset of masking, but this latency was similar to those recorded in background trials, indicating that successful performance did not depend on spending more time memorizing the numbers.

            In one testing session, after Ai had chosen the correct number and all the remaining items were masked by white squares, a fight broke out among a group of chimpanzees outside the room, accompanied by loud screaming. Ai abandoned her task and paid attention to the fight for about 20 seconds, after which she returned to the screen and completed the trial without error.

(Discussion)  

            Ai's performance shows that chimpanzees can remember the sequence of at least five numbers, the same as (or even more than) preschool children. Our study and others8-10 demonstrate the rudimentary form of numerical competence in non-human primates.

(PDF file also included Table 1 Performance in masking trials, which showed the response times and number correct for all trials in normal and masking condiitons. )

Supplementary information is available on Nature's World-Wide Web site (http://www.nature.com) or as paper copy from the London editorial office of Nature .

References

1.              Matsuzawa, T. Nature 315 , 57-59 (1985). Links   

2.              Matsuzawa, T., Itakura, S. & Tomonaga, M. in Primatology Today (eds Ehara, A., Kumura, T., Takenaka, O. & Iwamoto, M.) 317-320 (Elsevier, Amsterdam, 1991).  

3.              Murofushi, K. Jpn. Psychol. Res. 39 , 140-153 (1997).  

4.              Tomonaga, M., Matsuzawa, T. & Itakura, S. Primate Res. 9, 67-77 (1993).  

5.              Biro, D. & Matsuzawa, T. J. Comp. Psychol. 113 , 178-185 (1999).  

6.              Tomonaga, M. & Matsuzawa, T. Anim. Cogn. (in the press).  

7.              Miller, G. A. Psychol. Rev. 63 , 81-97 (1956).  

8.              Rumbaugh, D., Savage-Rumbaugh, E. S. & Hegel, M. J. Exp. Psychol. Anim. Behav. Process. 13 , 107-115 (1987). Links   

9.              Brannon, E. & Terrace, H. Science 282 , 746-749 (1998). Links   

10.           Boysen, S., Mukobi, K. & Berntson, G. Anim. Learn. Behav. 27 , 229-235 (1999).

Copyright Nature Volume 403 Number 6765 Page 39 - 40 (2000) . Dowloaded from the web March 31, 2000 (http://www.nature.com)