4. The Effect of Fear upon Habit Formation.—A certain amount of excitement undoubtedly promotes the formation of associations, but when the animal is frightened the opposite is true. I have no hesitation in stating that, in case of the green frog, any strong disturbing stimulus retards the formation of associations. Although the frogs gave little evidence of fear by movements after being kept in the laboratory for a few weeks, they were really very timid, and the presence of any strange object influenced all their reactions. Quiescence, it is to be remembered, is as frequently a sign of fear as is movement, and one is never safe in saying that the frog is not disturbed just because it does not jump. The influence of the experimenter's presence in the room with the frogs which were being tried in the labyrinth became apparent when the animals were tried in a room by themselves. They escaped much more quickly when alone. In order to keep records of the experiments it was necessary for me to be in the room, but by keeping perfectly quiet it was possible to do this without in any objectionable way influencing the results. It may be, however, that for this reason the learning is somewhat slower than it would have been under perfectly natural conditions. Early in this paper reference was made to the fact that the frog did not learn to escape from a box with a small opening at some distance from the floor if it was prodded with a stick. I do not mean to say that the animal would never learn under such conditions, but that they are unfavorable for the association of stimuli and retard the process. This conclusion is supported by some experiments whose results are tabulated at the bottom of Table IV. In these trials the animal had been trained to go to the left and to avoid red. At first ten trials were given in which the frog was in no way disturbed. The result was eight right choices and two wrong ones. For the next ten trials the frog was touched with a stick and thus made to enter the labyrinth from the box, A. This gave five right and five wrong choices, apparently indicating that the stimulus interfered with the choice of direction. Several other observations of this nature point to the same conclusion, and it may therefore be said that fright serves to confuse the frog and to prevent it from responding to the stimuli which would ordinarily determine its reaction.

5. The Permanency of Associations.—After the labyrinth habit had been perfectly formed by No. 2, tests for permanency were made, (1) after six days' rest and (2) after thirty days. Table V. contains the results of these tests. They show that for at least a month the associations persist. And although there are several mistakes in the first trials after the intervals of rest, the habit is soon perfected again. After the thirty-day interval there were forty per cent. of mistakes at the exit for the first series, and only 20 per cent. at the entrance. This in all probability is explicable by the fact that the colors acted as aids at the entrance, whereas at the exit there was no such important associational material.

TABLE V.

PERMANENCY OF ASSOCIATIONS. FROG NO. 2.

Tests after six days' rest (following the results tabulated in Table III.).

Trial.Entrance.Exit.
Right.Wrong.Right.Wrong
1-107382
(110-120)
11-20100100
Tests after THIRTY days' rest.
1-108264
10-20100100

D. Association of Stimuli.—In connection with reaction-time work an attempt was made to form an association between a strong visual stimulus and a painful electrical shock, with negative results. A reaction box, having a series of interrupted circuits in the bottom like those already described for other experiments, and an opening on one side through which a light could be flashed upon the animal, served for the experiments. The tests consisted in the placing of a frog on the wires and then flashing an electric light upon it: if it did not respond to the light by jumping off the wires, an electrical stimulus was immediately given. I have arranged in Table VI. the results of several weeks' work by this method. In no case is there clear evidence of an association; one or two of the frogs reacted to the light occasionally, but not often enough to indicate anything more than chance responses. At one time it looked as if the reactions became shorter with the continuation of the experiment, and it was thought that this might be an indication of the beginning of an association. Careful attention to this aspect of the results failed to furnish any satisfactory proof of such a change, however, and although in the table statements are given concerning the relative numbers of short and long reactions I do not think they are significant.

TABLE VI.

ASSOCIATION OF ELECTRICAL AND VISUAL STIMULI. FROG No. 1a, 2a, 3a, 4a, 5a, A and Z.

Frog.Total No. Trials.Days.Result.
No. 1a18018Increase in number of long reaction toward end. No evidence of association.
No. 2a18017Increase in number of short reactions toward end. No evidence of association.
No. 3a18017Marked increase in the number of short reactions toward end. No other evidence of association.
No. 4a20019Slight increase in the short reactions. There were a few responses to the light on the third day.
No. 5a20020No increase in the number of short reactions. Few possible responses to light on second and third days.
Frog A25020No evidence of association.
Frog Z45028No evidence of association.