FIG. 6. Composite Reënforcement-Inhibition curve for momentary auditory stimulation, based upon amount of reaction. Frogs Nos. 1, 2, 3, 4. (Males and females.)
FIG. 7. Composite Reënforcement-Inhibition curve for momentary auditory stimulation, based upon number of reactions. Frogs Nos. 1, 2, 3, 4. (Males and females.)
Just as Figures 2 and 3 permit of direct comparison of the results of the measurement of the amount of reënforcement and inhibition for males and females, so Figures 4 and 5 make possible comparison in similar fashion of the number of reënforced and inhibited reactions for the sexes. It is to be noted that the two sets of curves, plotted on the bases of amount and number of reaction, agree in all important respects.
Figure 6 is the composite curve of amount of reënforcement-inhibition for the four animals; Figure 7 is the composite curve of the number of reactions reënforced and inhibited.
Summarily stated, the results of the experiments thus far described are: (1) The auditory stimulus of a quick hammer blow produces the maximum amount of reënforcement of tactual reaction when it is given simultaneously with the tactual stimulus; (2) as the interval between the auditory and the tactual stimulus approaches .35˝ the amount of reënforcement gradually decreases; (3) when given .35˝ before the tactual stimulus the auditory is practically without effect upon the tactual reaction; (4) as the interval increases above .3˝ inhibition begins to appear; (5) the inhibitory influence of the auditory stimulus is greatest when the interval is about .45˝; (6) when the interval is as long as .90˝ the auditory stimulus is again ineffective. It thus appears that the reënforcement-inhibition curve of this particular stimulus under the conditions described is representative of a neural process which completes itself, in passing through two phases, a positive phase (reënforcement) and a negative phase (inhibition), in about one second.
b. Prolonged auditory stimulation. The experiments previously described have proved that a momentary auditory stimulus, which when given alone never produces a visible motor reaction, either reënforces or inhibits the reaction to a tactual stimulus which it accompanies or precedes. The experiments now to be described were made for the purpose of ascertaining whether reënforcement and inhibition occur in the same way if the auditory stimulus is prolonged, instead of momentary.
In a trial series of experiments with frog No. 1, one hundred pairs of reactions were recorded for each of six intervals of auditory stimulation. The auditory stimulus was given by the ringing of an electric bell. For all intervals the ringing of the bell continued until the tactual stimulus was given. When the two stimuli were given simultaneously the auditory stimulus was necessarily momentary, as in the foregoing experiments, but for all other relationships of the stimuli the bell rang for a certain length of time before the tactual stimulus was given. The six relations of the stimuli were: (1) simultaneous, (2) bell .2˝ before and until tactual, (3) bell .6˝ before, (4) bell 1.05˝ before, (5) bell 1.5˝ before, and (6) bell 2.0˝ before. The other conditions of these experiments were the same as those previously described, except that the auditory stimulus was here given by the opening of the key which released the pendulum, instead of being given by the turning of a key in the course of the pendulum swing. This method of giving the auditory stimulus as the pendulum was released was found unsatisfactory because of the irregularity of the magnetic release; at one time the pendulum would start immediately, at another time there would be a delay of as much as .1˝.