時間, 空間および速度評価の発達的研究 III

特に速度評価について

抄録

The present experiment is designed to systematically examine interactions of time, space and velocity in estimation at the field of motion perception. In this paper, the author will report only the results of velocity estimation.
The procedure is as follows: The standard stimulus, a light patch, moves from right to left on the right side of the screen, in accordance with the conditions shown in Table 1. One second after the standard stimulus disappears, the reproduction stimulus, another light patch, appears on the left side of the screen. The subjective velocity is measured by adjusting the reproduction stimulus to the phenomenal velocity of the standard stimulus by the method of reproduction. As you see in Table 2, there are four experimental sessions corresponding to four standard velocities, each of which contains five conditions of the standard stimuli. The orders among four sessions and among five conditions in each session are both at random for each subject. Each subject is assigned single trial for each conditions of the standard stimulus. Subjects are 16 1st grade children, 16 4th grade children and 16 university students. A half of subjects in each group is female and the other half is male.
Results are as follows:
1. In all groups constant standard velocity, 1.8, 3.2, 5.8, or 10.5cm/sec, is significantly overestimated, as exposure time and spatial distance of standard stimulus become smaller. This tendency is stronger in female than in male (see Fig. 1 and Tables 3 and 4).
2. For each sex, four lines by ratios of reproduced velocities to standard velocities for the four standard velocities drawnearly one curved line, when exposure times of standard stimuli are set in abscissa (see Fig. 2).
These findings are tentatively explained neurophysiologically. On the one hand, it is known that when certain receptor is stimulated continuously sensory adaptation occurs and frequency of neuronal discharge declines. On the other hand, it has been reported that in comparative primitive vertebrates such as frogs, rabbits and pigeons, some ganglion cells in retina respond only to a moving stimulus with certain direction and that in such cells in the frog retina the relation between neuronal discharge rate and the angular velocity of the moving stimulus is expressed as an increasing monotonic function. These facts suggest that in pursuit eye movement a moving stimulus of the certain physical velocity with long exposure time raises sensory adaptation of certain directionally sensitive cells in retina more strongly and frequency of neuronal discharge in the cells decreases more strongly and then perceived velocity becomes smaller than in the case of a moving stimulus of the same physical velocity but with short exposure time. But in primates or other higher mammals no cells that are specifically sensitive to movement have been found in retina and lateral geniculate nucleus. Such cells have, however, been found in visual cortex of a cat. Therefore, neurophysiological explain for our results may be not so simple as the above. But it does, at least, seem probable that effects of time (and space) on velocity estimation are caused more neurophysiologically than effects on time or space estimation.