SPATIAL WORKING-MEMORY SCORE OF HUMANS IN A LARGE RADIAL MAZE, SIMILAR TO PUBLISHED SCORE OF RATS, IMPLIES CAPACITY CLOSE TO THE MAGICAL NUMBER 7-PLUS-OR-MINUS-2

To compare the working memory CWM) capacity of humans to rats, we tested humans with a 17-arm radial maze and, in a follow up experiment, with a 13-arm radial maze. Both mazes were 15.2 meters in diameter, painted on a grassy field. In one version of the 13-arm experiment, we required a concurrent nonsense vocalization to impede subjects' use of language to remember locations. Subjects were instructed to choose arms of the radial maze unsystematically-as rats generally appear to do-and to visit the end of each arm only once. In additional procedures, we tested working memory capacity in a verbal task that is more analogous to the radial maze than is the typical ordered recall test. Subjects were asked to try to recite a sequence of 17 numbers (i.e., 18 through 34) or letters (A through Q) in unsystematic order, with no repeats. In another experiment subjects recited 13 numbers (14-26) or letters (A-M). In all tests, subjects were allowed only as many responses as there were distinct items (17 or 13, respectively). Average correct-response (nonrepeat) scores were 14.4 for the 17-arm maze and 14.1 for both of the verbal 17-item tests; these scores are close to the reported score for rats in a 17-arm radial maze. Average scores were between 10.8 and 11.4 in all of the 13-item maze and recitation tasks. When a simple mathematical model is used to take the probability of guesses into account, all these empirical results correspond to a reliable memory capacity that is near the high end of the range of the classical magical number 7 +/- 2 for the number of items that can be stored in short-term memory (STM).