Estimation of Visually Perceived Closure Rates

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Abstract
The ability of subjects to estimate the relative distance travelled by a luminous object approaching on a collision course and viewed in an otherwise stimulus free field has been investigated. This research stems from an analysis of visual skills anticipated for certain manned space vehicle operations. The stimulus object at onset bad an angular subtense of 4, 12, or 36' of arc. It approached at two velocities from five starting distances, thus yielding a total of 30 experimental conditions. The subjects' task was to indicate when the stimulus object bad traversed one-half of the original distance. Large constant and variable errors were evident in the estimates of subjects with no training at the task. Subjects provided with training, through knowledge of results after each estimate, demonstrated a considerable reduction in both constant and variable errors. After training, subjects were able to estimate when the object had reached the half-way point with an accuracy such that 50 per cent of the half-way estimates fell within a range equal to 5 per cent of the initial observation distance.

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