Abstract
Two experiments were conducted to investigate subject performance on the basis of two criteria, zero and 100 percent legibility of moving targets. A modified method of limits was employed. The targets consisted of black alphanumeric symbols regularly spaced 7.5 degrees apart on a brightly illuminated white background. Each target subtended an angle of 39 min. Legibility of the symbols was determined as they moved vertically from top to bottom in a frontal plane. The mean angular velocities for both the zero and 100 percent legibility performance levels were found to be approximately three times higher for the 7.5 degree symbol spacing than their respective velocities for a previously determined 1.5 degree symbol spacing. Performance was approximately twice as good with a 30 degree aperture as with a 3 degree aperture.
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