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Brett Fajen, Jonathan Matthis; Visual and non-visual contributions to the perception of object motion during self-motion. Journal of Vision 2011;11(11):920. https://doi.org/10.1167/11.11.920.
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When one moves in the presence of other moving objects, optic flow includes a component due to self-motion and a component due to object motion. Contrary to established theories of interception and obstacle avoidance, selecting actions and guiding locomotion relative to moving objects requires the visual system to recover the object-motion component. Formally, this can be achieved by using visual and/or non-visual self-motion information to discount the influence of self-motion, such that the remaining component is entirely due to object motion. Previously, we demonstrated the contribution of non-visual self-motion information in recovering the object-motion component (Fajen & Matthis, submitted). In this study, we directly tested the contribution of visual self-motion information. Two experiments were conducted in an immersive virtual environment viewed through a head-mounted display. In Experiment 1, subjects walked toward a gap between a pair of converging obstacles, and were instructed to judge before reaching the gap whether they could safely pass through it. On a small percentage of catch trials, the visual gain was increased such that subjects moved relative to the stationary background 50% faster than normal. Their movement relative to the obstacles was not affected. Subjects were more likely to judge gaps as impassable on catch trials, demonstrating the influence of visual information about the magnitude of self-motion on the perception of object motion. In Experiment 2, we tested the influence of visual information about the direction of self-motion by manipulating subjects' direction of movement through the virtual environment. As in Experiment 1, this manipulation did not affect subjects' movement relative to moving obstacles. Judgments were again consistent with an influence of visual self-motion information. Taken together with previous research, the findings suggest that people rely on both visual and non-visual self-motion information to recover information needed to guide locomotion relative to moving objects.
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