Perception and Control of Locomotion
Annual technical rept. 1 Sep 1993-31 Aug 1994
WRIGHT STATE UNIV DAYTON OH DEPT OF PSYCHOLOGY
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This report describes an empirical study to evaluate the ability to track a constant altitude as a function of the structure in optical flow Manipulated using types of ground texture - splay, depression, dot, and block and the rate of forward motion - global optical flow GOF rate. Subjects were asked to track a constant altitude 25 ft in the face of disturbances to the vertical, lateral, and fore-aft axes. The critical independent variables were texture type and GOF rate. Texture type was manipulated within subjects and GOF rate was manipulated between subjects. Dependent variables included RMS altitude error and correlated control power. The results showed a crossover interaction. For both dependent measures, performance at O GOF rate was best with depression angle and poorest with splay angle. The reverse was true at a GOF rate of 3 eyeheightss. The results are consistent with the hypothesis, suggested by Flach et al. 1992, that the ability to pick-up information about altitude from optic flow depends on the amount of optical flow activity specific to altitude signal relative to the flow activity arising from other factors e.g., motion in the fore-aft and lateral axes noise. The optical flow that results from forward motion GOF rate is visible in the depression, dot and block textures. This noise makes it more difficult to differentiate the optical activity specific to changes in altitude. With splay texture, there is no change in the flow as a result of forward motion. Therefore, performance with splay texture is independent of GOF rate.
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