Evaluation of a Phantogram Groundplane for the Study of Visually Guided Walking Behavior.

Humans in the natural environment are able to maintain efficient and stable gait across complex terrain. In part, this is because visual feedback is used to guide changes in heading, foot placement, and posture. However, the role of vision in the control of gait is not well understood. We present a novel methodology for the study of visually guided walking over complex terrain in a laboratory setting. A perceptually three-dimensional ground-plane is projected upon a physically flat laboratory floor, similar to a one-plane CAVE environment. The percept of height is reinforced through the use of stereoscopic shutter glasses, and by the dynamic updating of the projected image to maintain the coincidence of the accidental perspective with the subject's motion-tracked head position. The benefits of this "phantogram" groundplane are numerous. Obstacle height, shape, and location can be instantaneously manipulated. Because the groundplane is physically flat, the likelihood of falls is dramatically reduced. Because head position and object positions are known, the environment facilitates the computational analysis of eye-tracking data. The apparatus also opens the possibility of real-time manipulations of the environment that are contingent upon the participant's behavior. In summary, the apparatus facilitates rigorous hypotheses testing in a controlled environment, presumably, with minimal degradation to the visual experience. We have tested this assertion in a validation study. The subject was asked to approach and step over an obstacle of three possible heights, scaled in units of leg length, and randomized between trials. Between blocks, the obstacle was varied between a real-world or phantogram type. Data shows that subjects treat the phantogram and real-world obstacles similarly, thus validating the methodology for the study of naturalistic walking behavior. Meeting abstract presented at VSS 2015.