Ideational Behavior of Monkeys and Apes.

The reactive tendencies of two monkeys and a young orang utan have been studied by means of the method of multiple choices described in a previous communication to the Academy' and by certain supplementary methods. Four multiple choice problems were presented: (1) the problem of choosing from among any group of mechanisms the one at the left; (2) the second from the right end; (3) alternately, the first at the left end and the first at the right end; (4) the middle mechanism. Each of the three primates in question solved problem 1. One monkey (P. rhesus) required 70 trials; the other (P. irus), 132 trials. The ape succeeded only after 290 trials. The behavior of these three animals was most interesting and illuminating. P. irus was erratic, easily fatigued or discouraged, and apparently of low grade intelligence. P. rhesus, on the contrary, was alert, businesslike, intent on his task, and direct in his attack on experimental devices. The orang utan was childlike in his desire for assistance, as also in his resentment of annoyances or disappointments. He was given to settling down to a simple routine. The accompanying figure 1 presents the curves of error for these animals as constructed from the data in connection with problem 1. P. rhesus (Sobke) quickly and regularly eliminated mistakes and completely solved the problem. His disposition as well as his achievement, is pictured by the curve of errors. P. irus (Skirrl) exhibited marked irregularities of performance, and the curve indicates his variable attention and effort as well as his slow progress toward success. The orang utan (Julius) reacted uniquely, as his curve suggests. At the very outset, he developed a definite habit of response which, as it happened, was inadequate for the solution of the problem but yielded constantly 60% of correct first choices. The habit or reactive tendency was that of choosing each time the box nearest to the starting point. Julius continued to use this method without variation for eight successive days. Then a break occurred, but after a few days he settled back into the old rut. At the end of 230 trials, it was decided to try to destroy the ape's unprofitable habit. This attemptwas made by using 639