Animal intelligence: Experimental studies

by Edward L. Thorndike

I will describe some of the experiments in detail and then discuss the graphic presentation of them all.

Experiments with No. 1

Having developed in No. 1 the habit of coming down to the bottom of his cage to get a bit of food when he saw me reach out and take such a bit from my desk, I tested his ability to discriminate by beginning to use now one hand, now the other, feeding him only when I used the left. I also used different sets of words, namely, ‘I will give some food’ and ‘They shall not have any.’ It will be seen later that he probably reacted only to the difference of the hands. The experiment is similar to that described on [pages 129 and 130] of Chapter II. At the beginning, it should be remembered, No. 1 would come down whichever hand was used, no matter what was said, except in the occasional cases where he was so occupied with some other pursuit as to be evidently inattentive. He did come to associate the act of going down with the one signal and the act of staying still or continuing his ordinary movements with the other signal. His progress in learning to do so is best seen in the curves of his errors. To the ‘yes’ signal he responded correctly, except for the occasional lapses which I just mentioned, from the start and throughout. With the ‘no’ signal his errors were as shown in [Fig. 30], a. The break in the curve at 110 and 120 is probably not significant of an actual retrograde as the trials concerned followed an eight days’ cessation of the experiments.

I next tried No. 1 with an apparatus exposing sometimes a card with a diamond-shaped piece of buff-colored paper on it and sometimes a card with a similar black piece. The black piece was three fourths of an inch farther behind the opening than the other. The light color was the ‘yes’ signal. The error curves for both signals are given, as No. 1 at the beginning of the experiment did not go down always ([Fig. 30], b and b₁).

I next tried No. 1 with the same apparatus but exposing cards with YES and N in place of the buff and black diamonds. The record of the errors is given in [Fig. 30], c and c₁. At the start he came down halfway very often. This I arbitrarily scored as an error no matter which signal it was in response to. It should not be supposed that these curves represent two totally new associations. It seems likely that the monkey reacted to the position of the N card in the apparatus (the same as that of the black diamond card) rather than to the shape of the letters. On putting the black diamond in front he was much confused.

I next gave No. 1 the chance to form the habits of coming down when I rapped my pencil against the table twice and of staying where he was when I rapped with it once. He had 90 trials of each signal but failed to give evidence of any different associations in the two cases.

Experiments of this sort were discontinued in the summer. In October I tried No. 1 with the right and left hand experiment, he being in a new room and cage, and I being seated in a different situation. He came down at both signals and failed to make any ascertainable progress with the no signal in 80 trials. (October 20-24.)

Fig. 30.