Tests after THIRTY days’ rest.
1-10                8          2         6         4
10-20               10          0        10         0

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.  Days.  Result. 
Trials.

No. 1a 180 18 Increase in number of long reaction
toward end.  No evidence of association.

No. 2a 180 17 Increase in number of short reactions
toward end.  No evidence of association.

No. 3a 180 17 Marked increase in the number of
short reactions toward end.  No other evidence
of association.

No. 4a 200 19 Slight increase in the short reactions. 
There were a few responses to the light on the
third day.

No. 5a 200 20 No increase in the number of short reactions. 
Few possible responses to light on second and
third days.

Frog A 250 20 No evidence of association.

Frog Z 450 28 No evidence of association.

To all appearances this is the same kind of an association that was formed, in the case of the labyrinth experiments, between the tactual and the electrical stimuli.  Why it should not have been formed in this case is uncertain, but it seems not improbable that the light was too strong an excitement and thus inhibited action.  There is also the probability that the frog was constrained by being placed in a small box and having the experimenter near.