Perception of a thick transparent object is affected by object and background motions but not dependent on the motion speed

摘要

While a thick transparent object such as glass ball is in front of a textured background, the texture is perceived as distorted through the object. This distortion field is a cue for judging refractive index of transparent objects (Fleming, J?¤kel, & Maloney, 2011). We aimed to investigate effects of the dynamic distortion field on judging the refractive index of transparent objects. A test and a matching stimulus were presented adjacently on a CRT monitor, and subjects were asked to adjust the refractive index of the matching stimulus to make its material identical to the test stimulus. In Experiment 1, the test stimulus was randomly chosen from stimuli of five refractive indices (1.3-1.7), and either rotated around the vertical axis or remained stationary. The matching stimulus was always stationary and subjects could change its refractive index. We found that the perceived refractive index was higher with the moving object than the static object. In Experiment 2, the background texture of the test stimulus moved horizontally back and forth instead of object motion, and we found that the background motion also increased the perceived refractive index. We varied the background-motion speed (38 to 300% of Experiment 2) in Experiment 3. We confirmed the overestimation effect of the moving background, and we found that the degree of the overestimation was independent of the motion speed. In conclusions, the dynamic distortion field caused by object- or background-motion raised the perceived refractive index, but its motion speed did not matter. Thus the results cannot be explained by overestimation of distortion field by its dynamic change. Rather the dynamic distortion field may make the perceived rigidity of the object more than the static distortion field, and induce the overestimation of refractive index since the rigid materials generally have higher refractive index than the non-rigid materials.