視的現象と刺激時間との関係について II

見えの長さ・大きさの縮小・衰退過程

抄録

It has been long since the fact was noticed that figure look smaller, paler and dimmer after prolonged inspection period. It goes without saying that we need to analyse the changing process of such phenomena with the increase of the stimulating time, in order to clarify the significance of the temporal factor in visual phenomena. We made it clear in the former report that there is growing process under the short stimulating time. And, we expect that after the growing process is over, the decaying process may begin. We tried to make clear by quantitative measurements of the perceived length and size in connection with prolonged inspection in this study. The results were as follows :
1. The perceived length of a line ends its growing process at about ten seconds, and then the decaying begins. And, it seems that with some subjects the decay will not reach its maximum even after four minutes.
2. Up to the stimulating time of 5 seconds, the overstimation coccurs. It is conceivable that this happened because we used the variable stimuli which were exposed for one second, as the measure.
3. The same occurred when the variable stimuli were exposed for two seconds, as the measure. This fact seems to support our supposition mentioned above, as the degree of the overstimation in the latter case is less than that in the former case.
4. But, we could hardly find any difference between the two exposure, with regard to the tendency of increasing understimation rate in the stimulating time of over ten seconds. This indicates that we must consider the interaction between the standard and the variable figure which might produce some effect on the judgments.
5. Although the measures are dependent upon the various experimental conditions, it has been made clear that the perceived length of a line ends its growing process in the stimulation time about five seconds, and then its decaying process begins and the underestimation rate increases.
6. There is no difference in the tendency between the two stimulus intensities of 5 and 20 radlux, excepting that the degree of the underestimation in the former is less than that in the latter, and that in the former the underestimation rate gets to the maximum in the stimulating time of four minutes with all subjects.
7. The decaying process of the perceived size of a square is not different from that of a line.
8. But, the underestimation rate gets to the maximum in 2 minutes. The reason seems to be becoause the stimulus intensity is only 5 radlux.
We must consider that corresponding to the temporal process of visual phenomena, the psycho-physical field, constructed by us, goes through the decaying process after the forming process has passed. Supposing that the current distribution corresponding to the strength of the field as Köhler did, we may understand the forming process of the field as the temporal process of the current distribution owing to the specific nature of the medium in the nervous center. And, likewaise, we may understand the decaying process of the field as the results of such current process and the inhibitory process caused by the increase of polarization.