Abstract
In aviation, effective execution of some flight maneuvers, such as rescue operations at sea, requires that pilots form a veridical perception of their position and motion with respect to the environment. Previous research has shown that human observers can determine their own motion or spatial orientation from displays simulating observer motion through a rigid three-dimensional environment (Stoffregen, 1985; Andersen & Dyre; 1987; Dyre & Andersen, 1988; Andersen & Dyre, 1989;), however, the sensitivity of spatial orientation to noise in the visual field has not been examined. The present study examined the sensitivity of spatial orientation to noise in the global optic flow field. Displays simulating observer motion along the line of sight through a volume of randomly positioned points were observed monocularly through a circular window that limited the field of view to 30 degrees. The velocity of each display varied according to a function that was the sum of four sine functions of prime frequencies (between 0.15 and 1.0 Hz). Noise was produced by randomly shifting the phase lag of the three-dimensional motion function for each individual point within the display. Two levels of lag were examined: no lag and 10 second lag. Change in posture was used as an objective measure of spatial orientation and was recorded by a Kistler force platform. When no lag was present, increased postural sway was found to occur at all the frequencies of motion simulated in the display. However, for a lag of 10 seconds subjects exhibited no increase in postural sway at the display frequencies. These results suggest that if global optic flow patterns are obscured by noise then the information important for determining spatial orientation is greatly reduced. The importance of these results for flight maneuvers will be discussed.
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