Seeing transparent liquids from dynamic image distortion

摘要

??How can the human observer perceive transparent liquid? Transparent liquid often causes a distortion of an image below it due to refraction at the non-flat surface of the liquid. In accordance with non-rigid motion of the liquid surface, the pattern of image distortion dynamically changes. It is possible that the visual system interprets the dynamic image distortion not as a mere change in image, but as a dynamic distortion of a stable bottom image caused by the intervention of a transparent liquid. We therefore examined whether and how the visual system utilized dynamic image distortions as a cue for discerning a transparent liquid. We created computer graphics movies that simulate scenes in which a unidirectional flow of a transparent liquid, with the refraction index of water (1.33), ran in front of a variety of texture backgrounds. We removed specular reflection at the liquid surface to test the pure effect of image distortion. A rating experiment indicated that a strong impression of a transparent liquid was obtained with the movies. However, this impression collapsed either with a single static movie frame or with the movies presented with blank intervals of 100 msec between frames. These results indicate that the visual system can utilize the dynamic change in image distortion as a cue to discerning a transparent liquid. Indeed, a transparent liquid was perceived only by a dynamic random deformation of an image that had deformation statistics similar to the fluid movies. Further experiments clarified that the dynamic change of the coarse (4-16 cycles per image) image distortion had to be presented for approximately 200 msec to produce the strong impression of a transparent liquid. The results indicate that the temporal pooling of the spatially coarse image distortions underlies the perception of a transparent liquid.