JUDGMENTS OF ORDINALITY AND SUMMATION OF NUMBER SYMBOLS BY SQUIRREL-MONKEYS (SAIMIRI-SCIUREUS)

In Experiment 1, 2 squirrel monkeys (Saimiri sciureus) were given choi ces between all possible pairs of the arabic numbers 0, 1, 3, 5, 7, an d 9, with choice of any number yielding that number of pieces of peanu t as a reward. Both monkeys learned to choose the larger number in all pairings and learned to choose the largest number within a set of 4 n umbers. In Experiments 2-4, the monkeys were tested on problems in whi ch they chose between pairs of stimuli containing 2 numbers versus 2 n umbers, 1 number versus 2 numbers, and 3 numbers versus 3 numbers. Bot h monkeys showed a significant tendency to choose the stimulus that co ntained the largest sum. Various tests indicated that this effect coul d not be explained by choice of the stimulus with the largest single n umber, by avoidance of the stimulus with the smallest single number, o r by experimenter cuing.