Influence of optic flow on the control of walking toward a goal

Abstract

Although previous studies have shown that optic flow is used to control human walking, the relative effectiveness of various types of optic flow information and whether humans use their perceived visual heading to control walking toward a goal remain in question. Here we systematically varied optic flow information in the display and examined how it affected walking in an immersive virtual environment as well as passive heading perception. In the walking experiment, participants walked toward a target placed in front of them at 7 m in a virtual environment viewed through a head-mounted display (47°Hx38°V). We varied optic flow information in the display to examine the effects of target motion relative to the observer, sparse flow, expansion, and dense flow on the control of walking toward a goal. The visual heading was displaced ±10° from participants' physical walking direction, thus participants would walk on a curved path toward the target with mean heading error at 10° if they ignored optic flow and walked toward the target egocentric direction. In the parallel heading perception experiment, the displays matched those in the walking experiment, and participants used a mouse to move a probe to their perceived heading at the end of each 2-s trial. Participants walked on the least curved path toward the target when the display contained dense flow. Sparse flow resulted in higher curvature, independent of the expansion cue. Target motion relative to the observer affected walking only at close distances. The mean heading error data of walking are similar to the accuracy and precision data of heading perception. We conclude that visual heading defined by optic flow is used to guide walking toward a goal. The relative effectiveness of optic flow and target egocentric direction is due to the specificity of the information, not an internal cue weighting.