Two processes in the visual control of steering along a curving path: sensing turns and updating with respect to the path

Abstract

Steering a vehicle over a curving path can be performed well even without continuous visual feedback (Godthelp, 1986). The present experiment is concerned with the role of optic flow produced by ground texture when view of the path is intermittent. Using a wide-screen driving simulator of our design, subjects steered a curving single lane path defined by a sum of spatial sinusoids. Viewing of the path was continuous or intermittent (the most challenging condition being 1 visible frame out of 100 at a 60 Hz update rate), and there were 3 ground texture conditions (consistent flow, inconsistent flow, and no flow). In the consistent condition, optic flow from ground texture was consistent with the path being steered. In the inconsistent condition, ground flow corresponded to a traveled path different from that defined by the visible path but short-term changes in the flow were informative about vehicle turn rate. Although the path disappeared intermittently in these two conditions, the ground texture remained visible. In a third condition, both path and ground texture were occluded. Subjects continue to accurately steer during occlusion of the path even for low intermittencies (1 visible frame per second), as long as ground flow is available and consistent. Inconsistent flow has little effect for continuous viewing but it has a large deleterious effect for low intermittencies. Most importantly, absence of flow causes even greater degradations of steering performance than inconsistent flow. This means that inconsistent flow, while being misleading about vehicle heading (travel direction), is still informative about change in heading (turn rate). Thus, the experiment shows that subjects use intermittent views of the path to plan their steering actions and use flow from ground texture to sense vehicle turns even when that flow falsely specifies vehicle heading.