奧行知覚における遠方距離の過大視

抄録

1. Sterneck and Gilinsky assumest that the farther half of visually bisected distance is objectively not shorter than the nearer. The present investigation was undertaken to test the validity of this assumption in a space comparatively near to the observer in a dark room.
2. Experimental setting was a modification of the Bourdon's bright spot. A minute bright spot out of a dark box containing an electric bulb was used to mark the distance. On the side of the box toward the observer there was a circular hole covered with paper. Spots of different diameters were used for different distances, so that their phenomenal brightness was kept constant for all distances. Two bright spots placed at the level of observer's eyes were moved along tracks diverging at an angle of 3 degrees from the point of observation. Care was taken to remove all the reflected light from the bright spot and to remove any other secondary cues of distance.
3. With monocular vision every observer's discrimination of distance was entirely at sea. With binocular vision each observer was able to discriminate rather easily. Four observers who have normal visual (vernier) acuity gave the average depth acuity of 1.4′ in a two-spot setting, and 1.0′ in a three-spot setting. In both cases the values of depth acuity were consistent regardless of observation distance. These findings would mean that the visual factor participating in the measurements was confined only to convergence.
4. In an experiment which used the two-spot setting, bisections were performed by stopping a movable spot at a point that appeared to be just halfway between the observer and the stationary spot designating the total distance to be bisected (Table 4). In another experiment, the task of observer was to bisect the interval of 2 (Table 5) or 4 meters (Table 6) at various distances of observation. Each interval was presented by means of two spots ; one indicating the near-end and the other the far-end.
5. These experiments revealed that the phenomenal midpoint was farther than the objective one at the observation distance between 2 and 5 meters, in other words, the farther half of the distance was overestimated as compared with the nearer half. The amount of overestimation had a tendency to decrease in accordance with the increase in observation distance, though there were individual differences (Fig. 2).
6. It seemed that non-visual factor might participate in the process of the overestimation of farther distance, and that the overestimation might correspond with the overconstancy of size.