Abstract
Visual motion cues can be created by self-motion, by solid moving objects, and by non-solids such as gases or fluids. We wanted to determine what types of motion cues are available to the visual system when viewing gaseous, as opposed to solid, stimuli. In particular, we focus on cues available for estimating the motion-in-depth of smoke and its time-to-contact with an observer. While much is known about the visual cues available for estimating the motion-in-depth of solid objects (e.g., looming/optical expansion, binocular disparity, interocular velocity differences), little is known about how robust and reliable these cues are for estimating the motion of stimuli that change shape, size, and density in the environment. Principles from fluid dynamics can account for the 3D motion of smoke, but do not directly indicate what information is available to the human visual system. Thus, we examine the visual cues present in moving smoke and compare these to the cues for a similarly moving solid object. We provide descriptive statistics about looming, motion coherence, speed and angular movement for a range of stimuli, including videos of actual smoke and computer generated simulations. Our analysis shows that similar motion cues are present for solids and smoke, but provide different information about the distance and speed at which solids and smoke are moving. For example, looming may provide less information about motion direction for smoke than for solids. However, transparency provides a potential cue for smoke that is not present for solids. When relying on these cues, our results suggest that observers may perceive equivalently moving solids and non-solids as having different trajectories. Because typical observers likely have substantially more experience with solid motion, such perceptual differences may have implications for how people respond to smoke, for example, in building fires.
Meeting abstract presented at VSS 2017