Movement detection thresholds and stimulus duration

Movement detection thresholds were measured for varying exposures of a moving spot. A tradeoff was found in which an increase in duration (T) was offset by a decrease in the velocity required for detection (V). In the range of durations studied (about 50–700 msec), V × T was constant. The V × T constancy was interpreted in terms of the direct detection of movement as motion, and a comparison was made with Bloch’s law.