THE SPATIAL LIMIT FOR MOTION DETECTION IN NOISE DEPENDS ON ELEMENT SIZE, NOT ON SPATIAL-FREQUENCY

When a random spatial noise pattern is displaced for a short distance it seems to move coherently, but when the displacement exceeds a certa in value, the direction of motion cannot be clearly perceived. We meas ured the displacement limit (Dmax) for a two-frame sequence and found that it depended on the Size of the elements comprising the random pat tern, even when low spatial frequencies were removed from the pattern by spatial band-pass filtering. Dmax depended strongly on contrast for the filtered patterns, but less so for the unaltered patterns. The da ta support a model for low level motion detection in which the maximum motion displacement that can be detected is determined by the mean se paration of pattern elements, following a stage of low-pass spatial fi ltering, and in which the upper spatial displacement depends upon the pattern statistics, not upon the size of detectors in the visual syste m. (C) 1997 Elsevier Science Ltd.