4 experiments tested the perception by 11 rhesus monkeys of patterns of light-on, light-off presented in a 4 * 4 matrix of cells. Patterns consisting of 1, 2, or 4 lighted cells were exposed to Ss for a certain interval; then, after a predetermined delay, Ss were required to respond to each previously lighted cell in the matrix (i.e., to reproduce the pattern). Successful performance was inversely related to the number of sides in 4-light patterns while directly related to the dispersion of the lights. Symmetrical patterns were no more easily reproduced than asymmetrical patterns. Old Ss performed as well or better than middle-aged Ss on the short-delay intervals but were significantly inferior to the middle-aged Ss on the longer delays. (PsycINFO Database Record (c) 2006 APA, all rights reserved)