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Brian P. Dyre, Roger Lew; Environmental modulations of visually-induced steering errors resulting from non-rigid transparent optical flow. Journal of Vision 2008;8(6):1159. doi: 10.1167/8.6.1159.
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Non-rigid optical flow causes systematic errors in judgments of heading (Royden Hildreth, 1996; Warren & Saunders, 1995; Dyre, Richman, & Fournier, 2000), localization of the focus of expansion (FOE; Duffy & Wurtz, 1993), and steering control (Dyre & Lew, 2005). Such flow occurs when an observer moves through a fixed environment where an object (e.g., another vehicle) or a field of objects (e.g., snow or dust) moves independently. The direction and magnitude of error varies depending on the angular distance between the FOEs corresponding to the environment and the moving object(s): small angles move the apparent FOEs closer together (attraction errors) and larger angles move the apparent FOEs further apart (repulsion errors). The angle at which errors change from attraction to repulsion we call the cross-overangle. We examined how a variety of environmental manipulations modulate the overall magnitude and cross-over angle of steering control errors. Displays simulated forward translation over a textured plane with an independently-moving field of dots simulating blowing snow; the angle between the FOEs defined by the ground and dots varied. Participants controlled their yaw such that they appeared to move along a straight path over the ground. We found that: a) static direction cues in the form of lane markings of a straight roadway reduced steering error magnitude and shifted the cross-over angle, b) increasing local shearing motion by adding vertical poles fixed to the ground shifted the cross-over angle but had no effect on overall error magnitude, c) changing the optical speed of the moving dots shifted the cross-over angle, and d) changing the exponential lag of the steering control system had no effect on the pattern of errors. These results suggest that both motion contrast and induced motion contribute to illusory heading and inappropriate steering control induced by non-rigid transparent optical flow.
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