GUIDANCE OF LOCOMOTION ON FOOT USES PERCEIVED TARGET LOCATION RATHER THAN OPTIC FLOW

What visual information do we use to guide movement through our enviro nment? Self-movement produces a pattern of motion on the retina, calle d optic flow, During translation, the direction of movement (locomotor direction) is specified by the point in the flow field from which the motion vectors radiate - the focus of expansion (FoE) [1-3]. If an ey e movement is made, however, the FoE no longer specifies locomotor dir ection [4], but the 'heading' direction can still be judged accurately [5]. Models have been proposed that remove confounding rotational mot ion due to eye movements by decomposing the retinal flow into its sepa rable translational and rotational components ([6,7] are early example s), An alternative theory is based upon the use of invariants in the r etinal flow field [8]. The assumption underpinning all these models (s ee also [9-11]), and associated psychophysical [5,12,13] and neurophys iological studies [14-16], is that locomotive heading is guided by opt ic flow. In this paper we challenge that assumption for the control of direction of locomotion on foot. Here we have explored the role of pe rceived location by recording the walking trajectories of people weari ng displacing prism glasses. The results suggest that perceived locati on, rather than optic or retinal flow, is the predominant cue that gui des locomotion on foot.