Abstract
In the successive comparison of brightness, when the time interval between two stimuli is short, or when the ground is lighter than the stimuli, the positive time-error arises. In these two cases in wnich the positive time-error arises, a common factor seems to be operating. The results of our experiments suggest that the inhibitory effect exists in both cases as a common factor. When two stimuli are presented successively, the after-effect of the first excitation will remain in the nervous system. This after-effect will weaken the excitation of the second. Consequently the seocnd stimulus appears darker phenomenally. We name such an after-effect the inhibitory effect. We posit this effect as a physiological hypothesis. In the former theory of the time-error, arter-effect of the first excitation upon the next excitation has been neglected and the time-error has been explained only by the change in the trace of the first excitation. The results of our experiments have proved that the former theory is deficieat.
Our experiments of the successive comparison of brightness gave us the following results.
1. When the time interval between two stimuli is short, the after-effect of the first excitation inhibits the second one and pnenomenally the second stimulus appears darker. In such a way the postive time-error arises.
2. When the ground is lighter than the stimuli, the after-effect of the excitation by the ground preceding the stimuli inhibits the next excitation by the first stimulus, the trace of the first stimulus assimilates the trace of the ground between the stimuli, and tne after-effect of the excitation by the ground nhibits the next excitation by the second stimulus. The ground following the second stimulus does not essentially influence the judgment of comparison i.e. the timeerror because the snbjects make judgmemts as soon as the second stimulus is presented. In such a way the positive time-error arises.
3. The inhibitory effect has the following characteristics.
a) The longer the duration of the first excitation is, the stronger and longer does the inhibitory effect of the first excitation act on the second one.
b) The longer the time interval between the two excitations is, the weaker is the inhibitory effect of the first excitation upon the second one.
