Abstract

The observer viewed the center of a circular black area surrounded by a dimly illuminated area. A small moving spot of white light traversed the path of a horizontal line centered in the circle. At high speeds, the observer reported a stationary line and could not indicate the direction of movement. At slow speeds, he indicated the direction (right or left). Three subjects made observations for different combinations of luminance and speed of the moving spot.

The threshold luminance for visibility of either the moving spot or stationary line increased directly with the stimulus speed. The threshold luminance for discrimination of motion of the moving spot also increased directly with its speed but approached infinity for a limiting asymptotic velocity at high speeds. The upper speed threshold increased directly with luminance at moderate luminances. At intense luminances, the upper speed threshold was approximately constant (35° of visual angle per sec).

© 1958 Optical Society of America

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