The Mental Life of Monkeys and Apes | Page 7

was briefly as follows: A small quantity of food having been placed in each of the food cups and covered by the metal flanges on the exit doors, the experimenter raised door 11 of figure 17 and then opened door 10 and the door of the cage in which the desired subject was confined. After the latter, in search of food, had entered the runway D, the experimenter lowered door 11 to keep it in this runway, and immediately proceeded to set the reaction-mechanisms for an experiment (trial). Let us suppose that the first setting to be tried involved all of the nine boxes. Each of the entrance doors would therefore be raised. Let us further suppose that the right door is defined as the middle one of the group. With the apparatus properly set, the experimenter next raises door 12, thus admitting the animal to the response-compartment E. Any one of the nine boxes may now be entered by it. But if any except number 5, the middle member of the group, be entered, the entrance door is immediately lowered and both the exit and entrance doors locked in position so that the animal is forced to remain in the box for a stated period, say thirty seconds. At the expiration of this time the entrance door is raised and the animal allowed to retrace its steps and make another choice. When the middle box is chosen, the entrance door is lowered and the exit door immediately raised, thus uncovering the food, which the animal eats. As a rule, by my monkeys and ape the reward was eaten in the alleyway G instead of in the multiple-choice box. As soon as the food has been eaten, the exit door is lowered by the experimenter, and the animal returns by way of G and H to runway D, where it awaits its next trial.
As rewards, bananas and peanuts were found very satisfactory, and although occasionally other foods were supplied in small quantities, they were on the whole less constantly desired than the former.
Four problems which had previously been presented to other organisms were in precisely the same form presented to the three primates. These problems may be described, briefly, by definition of the right reaction mechanism, thus: problem 1, the first mechanism at the subject's left; problem 2, the second mechanism at the subject's right (that is, from the end of the series at the subject's right); problem 3, alternately, the first mechanism at the subject's left and the first at its right; problem 4, the middle mechanism of the group.
It was my intention to present these four problems, in order, to each of the three animals, proceeding with them as rapidly as they were solved. But as it happened, only one of the three subjects got as far as the fourth problem. When observations had to be discontinued, Sobke was well along with the last, or fourth problem; Skirrl was at work at the third problem; and Julius had failed to solve the second problem.
For each of the problems, a series of ten different settings of the doors was determined upon in advance. These settings differ from those employed in a similar investigation with the pig only in that the numbering of the doors is reversed. In the present apparatus, the boxes as viewed from the front (entrance) are numbered from the left to the right end, whereas those of the pig apparatus were numbered from the right end to the left end.
Below are presented for each of the several problems (1) the numbers of the settings presented in series; (2) the numbers of the doors open; (3) the number of doors open in each setting and for the series of ten settings; and (4) the number of the right door.

PROBLEM 1. First mechanism at left of group
Doors No. of No. of Settings open doors open right door 1..................1.2.3......................3..................1 2..................8.9........................2..................8 3..................3.4.5.6.7..................5..................3 4..................7.8.9......................3..................7 5..................2.3.4.5.6..................5..................2 6..................6.7.8......................3..................6 7..................5.6.7......................3..................5 8..................4.5.6.7.8..................5..................4 9..................7.8.9......................3..................7 10..................1.2.3......................3..................1 -- Total 35
PROBLEM 2. Second mechanism from the right end of group
Doors No. of No. of Settings open doors open right door 1..................7.8.9......................3..................8 2..................1.2.3.4....................4..................3 3..................2.3.4.5.6.7................6..................6 4..................1.2.3.4.5.6................6..................5 5..................4.5.6.7.8..................5..................7 6..................1.2.3......................3..................2 7..................2.3.4.5....................4..................4 8..................1.2.3.4.5.6.7.8.9..........9..................8 9..................1.2.3.4....................4..................3 10..................3.4.5.6.7.8................6..................7 -- Total 50
PROBLEM 3. Alternately the first mechanism at the left and the first at the right end of the group
Doors No. of No. of Settings open doors open right door 1..................5.6.7......................3..................5 2..................5.6.7......................3..................7 3..................1.2.3.4.5.6................6..................1 4..................1.2.3.4.5.6................6..................6 5..................4.5.6.7.8..................5..................4 6..................4.5.6.7.8..................5..................8 7..................2.3.4.5....................4..................2 8..................2.3.4.5....................4..................5 9..................3.4.5.6.7.8.9..............7..................3 10..................3.4.5.6.7.8.9..............7..................9 -- Total 50
PROBLEM 4. Middle mechanism of the group
Doors No. of No. of Settings open doors open right door 1..................2.3.4......................3..................3 2..................5.6.7.8.9..................5..................7 3..................1.2.3.4.5.6.7..............7..................4 4..................7.8.9......................3..................8 5..................4.5.6.7.8..................5..................6 6..................1.2.3.4.5.6.7.8.9..........9..................5 7..................1.2.3......................3..................2 8..................2.3.4.5.6..................5..................4 9..................3.4.5.6.7.8.9..............7..................6 10..................6.7.8......................3..................7 -- Total 50

It was found desirable after a problem had been solved to present a new and radically different series of settings in order to determine to what extent the subject had learned to choose the correct door by