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Abstract

When moving through space, both optic flow and locomotor (proprioceptive/efference copy, vestibular) information can be used to judge the extent of a traveled distance. To better understand how each of these cues is used to estimate the magnitude of self-motion, it is important to dissociate the relative contributions of each when both are available in natural, cue-rich environments. This study created a conflict between visual and locomotor distance cues by either magnifying (2.0×) or minimizing (0.5×) the information contained in the optic array using spectacle-mounted lenses. The experiment took place in a large, open, outdoor field with few landmarks in the distant periphery. Subjects viewed a static target in the distance (6, 8, 10, 12m) and reproduced this distance by walking. Three optical manipulations (OMs: 2.0×, 1.0×, 0.5×) occurred either: A) during the initially learned visual preview, B) during the walked response, or C) during both learning and responding (same OM in each phase). When wearing the 2.0× lenses during the visual preview subjects produced estimates that were shorter than those produced when wearing the 1.0× lenses. The reverse effect was observed for the 0.5× lenses (significantly longer). Although these under/overestimations of static visual distance are significant in the predicted direction, the magnitude of the effect is less than expected considering the specifications of the lenses. In contrast, when the OM occurred during the walked response there were no lens-related effects, thus suggesting a reliance on locomotor cues. When the OM occurred during both learning and responding, lens-related effects were again observed in the expected directions, although were not as strong as when the OM occurred during the visual preview alone. Overall, the results suggest that locomotor information can be used effectively to reproduce a learned visual distance and appears to be the dominant cue when walking with magnified/minimized optic flow.