Monkeys play by the numbers.

Abel sits in front of his computer and eyes the bright cursor at the center of the blank screen. Five numerals pop onto the screen, randomly arrayed around the cursor. Abel grasps a joystick and directs the cursor to the numeral 8; eight fruit-flavored treats shoot into a dispenser at his side. Happily munching away, he sends the cursor to the numeral 6, then 5, then 4 and finally 1. Each time, he receives a corresponding number of treats.

Abel may not qualify as an ace mathematician, but he and a buddy named Baker -- both rhesus monkeys -- display a facility for ordering numerals beyond that demonstrated with any other nonhuman animals, assert David A. Washburn and Duane M. Rumbaugh, psychologists at Georgia State University in Atlanta. The monkeys' surprising ability to go from larger to smaller numerals does not necessarily mean that they count as humans do, the researchers note in the just-released May PSYCHOLOGICAL SCIENCE. Abel and Baker may have learned either to associate specific quantities with numerals from 0 to 9 or to assign relative values to the symbols by concluding that 9 stands for more treats than all other numerals, 8 stands for more treats than all other numerals except 9, and so on.

The monkeys first learned to distinguish between two numerals presented on the screen. After several hundred trials, Abel and Baker generally chose the larger numeral. In subsequent tests, they usually chose the numeral of greater value from novel combinations and from arrays of up to five numerals. Overall scores ranged from about 70 to 100 percent correct, with more errors on trials with more numerals on the screen and greater differences between numerals.

In previous experiments with chimpanzees, dolphins, birds and other animals, researchers have had difficulty demonstrating knowledge of an ordered series of numbers, although one chimp displayed an apparent ability to count and add up to 4 (SN: 5/23/87, p.334; 8/27/88, p.140).