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William B. Thompson, Betty J. Mohler, Sarah H. Creem-Regehr; Does perceptual-motor recalibration of locomotion depend on perceived self motion or the magnitude of optical flow?. Journal of Vision 2005;5(8):386. doi: 10.1167/5.8.386.
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The perceptual-motor calibration of human locomotion can be manipulated by exposure to an environment in which the visual flow associated with self-motion is altered relative to biomechanical walking speed (Rieser, Pick, Ashmead and Garing 1995, JEP:HPP). An open question remains as to whether this recalibration is based on perception of the speed of movement through the world or on the magnitude of optic flow itself. We addressed this issue using a treadmill-based virtual environment in which we could independently vary actual walking speed and the simulated visual experience of moving down a hallway. The hallway consisted of textured walls and textureless floor and ceiling, so that visual flow information was only available from the walls. Subjects were exposed to one of two conditions. Actual walking speed was 1.2m/s in both cases. In one condition, visual information corresponded to movement down a long hallway at a speed one third less than the biomechanical rate of walking. In the second condition, the visual information corresponded to movement three times faster than in the first condition, down a hallway that was three times larger. Because the scale of the space was increased by the same amount as the increase in velocity through the space, the magnitude of optic flow remained essentially constant, though flow due to the walls moved upward in the visual field. Perceptual-motor calibration was evaluated by having subjects walk blindfolded to previously viewed targets at 6, 8 and 10m before and after 10 minutes of walking on the treadmill. For the visually slower condition, subjects increased the distance they walked by an average of 10% between the pre and post tests. For the visually faster condition, subjects decreased the distance they walked by an average of 3%. These differences demonstrate that the recalibration depended at least in part on visual perception of the speed of self-movement, not just on the magnitude of optic flow.
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