感覚融合に関する研究 (I)

Abstract

The present investigation was designed to study the effect of area and exposure time of stimulus upon the fusion time of visual sensation. In the dark room two flashes of light were presented successively at an identical location for equal brief durations. Two kinds of thresholds were measured. One of them Was the threshold of fusion and this was defined as. the longest time internal between the two stimuli which produced a single impression (tf), and the other was the threshold of separation and this was defined as the shortest time interval which produced an impression that the second stimulus appeared after the complete disappearance of the first stimulus, i. e., the shortest time interval for perceiving dark interval between the stimuli (ts). So the present experiment was different from the flicker experiment in several points. Using the monocular and foveal vision, the following results were obtained.1. As the area of stimulus was enlarged, ts became smaller. But after ts reached its minimum value at some area, it remained approximately constant within some range of area, then it increased when the area was further enlarged. The value of tf was much smaller than ts, and, in addition, tf became smaller when the stimulus area was enlarged.2. As the exposure time of stimulus was lengthened, ts became smaller.3. Regardless of the length of the exposure time, tf remained approximately constant.4. Presenting two stimuli in differentloci successively, the threshold of simultaneity (tsi) was measured for comparable time interval to the above tf. The threshold of simultaneity was defined as the longest time interval that both stimuli appeared simultaneously. It was found that tsi increased in proportion to the logarithm of the visual angle between the stimuli within 19 degrees of visual angle. When both the visual angle and the perceived distance between the stimuli were held constant, the value of tsi remained the same, regardless of the variation in the objective distance between the stimuli on the one hand and the observing distance on the other.