Abstract
When a thick transparent object is located on a textured background, its distortion field is a cue for perceiving index of refraction (Fleming, et al., 2011). Object motion and self-motion enhance the glossiness perception (Tani, et al. 2013). Since it is unknown whether the self-motion or motion parallax improves the perception of refractive index, we aim to investigate effects of object motion and self-motion on the perception of thick transparent materials. One of transparent bumpy objects (test stimulus) in front of a random-texture background was presented on a CRT monitor for 6 s, followed by a similar but different-shape matching stimulus. Twenty participants monocularly observed them, and they were asked to adjust the refractive index of the matching stimulus to make its material identical to the test stimulus. 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 participants observed it with or without head motion rightward and leftward at 0.5Hz. When the object moved with self-motion, the object’s retinal image moved synchronously with the head motion by a 3D tracker (valid motion-parallax). The matching stimulus was always stationary without self-motion. We found that the object motion without the head motion decreased the perceived refractive index, but the combination of the object motion and the self-motion significantly improved the perception of the refractive index (p< .001, ηp2=.585). These results suggest that the retinal image motions of transparent materials could not be perceived accurately without motion parallax, but rather they might be perceived like as non-rigid objects (cf. Kawabe, et al. 2015). Thus, it might decrease the perceived refractive index. However, the valid motion parallax contributes to perceiving the accurate shape and refractive index of transparent materials.
Acknowledgement: Supported by Grant-in-Aid for Scientific Research (A) #18H04118