Accuracy of walking direction with and without visual feedback

Abstract

Direction of self-motion during walking is indicated by multiple cues, including optic flow, non-visual sensory cues, and motor prediction. I measured the variability in walking direction with and without visual feedback, and tested whether visual and non-visual cues are weighted in an optimal manner. Open-loop walking in an immersive virtual environment was used to assess the accuracy of perceived walking direction. Observers walked toward a target 4m away either with no vision, or vision during the first 1m of walking. Three simulated environments were tested: target-only, target and textured ground, or target with textured ground and scattered posts. With no vision, variability in walking direction averaged 3°. Visual feedback during initial movement reduced variability to about 1.5°, regardless of visual environment. These results show that observers are capable of initiating movement toward a target with reasonable accuracy, but that even a limited amount of visual feedback significantly improves accuracy. Based on these measures, an optimal estimator would strongly weigh visual information. A second experiment measured the perceptual weighting of visual and non-visual cues. Optic flow specified a conflicting heading direction (±5°), and bias in walking direction was used to infer cue weights. Visual heading had a significant effect on walking direction, but the estimated visual weights were smaller than predicted (33-43% vs. 71%), and varied depending on the visual environment. Non-visual information appeared to have more influence than expected given the relative reliability of cues.