2007 年 25 巻 2 号 p. 267-268
It has been proposed that objects which appear to be expanding, and represent approaching objects, are easier to detect than objects which appear to be contracting (Takeuchi, 1997; Shirai & Yamaguchi, 2004). To investigate this asymmetry in a visual search task we examined the detection of approaching and receding objects which were defined by moving cast shadows. The results showed that an "approaching" target among "receding" distractors was detected faster and more accurately than a "receding" target among "approaching" distractors (Experiment 1). In addition, this asymmetry did not occur if the luminance of the shadows was lighter than the background (Experiments 2 and 3. These findings suggest that the asymmetry of the perception of motion-in-depth could be caused by the depth information of cast shadows.