Abstract
Human observers easily recognize complex natural phenomena, such as flowing water, which often generate highly chaotic dynamic arrays of light on the retina. It has not been clarified how the visual system discerns the source of a fluid flow. Here we show that the magnitude of image deformation caused by light refraction is a critical factor for the visual system to determine the perceptual category of fluid flows. Employing a physics engine, we created computer-rendered scenes of water and hot air flows. For each flow, we manipulated the rendering parameters (distortion factors and the index of refraction) that strongly influence the magnitude of image deformation. The observers rated how strongly they felt impressions of water and hot air in the video clips of the flows. The ratings showed that the water and hot air impressions were positively and negatively related to the magnitude of image deformation. Based on the results, we discuss how the visual system heuristically utilizes image deformation to discern non-rigid materials such as water and hot air flows.
Highlights
Natural scene images were added as background to the simulated scenes
By combining graphical simulations of the transparent flow, image motion analyses, and psychological measurements, we found that the magnitude of image deformation is the strong determinant of the source of transparent flows in perception
It is logically plausible to assume that in order to differentiate the source of a transparent flow on the basis of the magnitude of image deformation, the visual system needs to first recognize that an image deformation arises from an optical deformation due to light refraction at the surface of transparent materials, not from the physical deformation of scenes/objects themselves
Summary
Natural scene images were added as background to the simulated scenes. We chose ten images out of the rich collection in the McGill Calibrated Color Image Database[19]. The selected images can be seen in Supplementary Figure 1. We used all or part of the chosen ten images. In Experiment 1, we used a single static video frame of the video clips of actual hot air as background. Comparison between clips of real and simulated hot air flows Observers.
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