Effects of pattern element density upon displacement
limits for motion detection in random binary
luminance patterns

M.J. Morgan and M. Fahle



The upper motion displacement threshold (Dmax) was determined with twoframe motion sequences of random binary luminance patterns, over a range of pattern element sizes and densities. Dmax was little affected by density at small element sizes (less than 5 arcmin), in agreement with previous reports. However, at larger element sizes (greater than 9 arcmin) Dmax increased as element density was reduced in the range 505%. We explain our findings by a model which takes into account spatialfrequency filtering prior to motion detection, and the effects of pattern density upon the statistics of random binary patterns. We also implicate the dependence of Dmax upon the contrast energy of the elements in broadband patterns, and provide a direct demonstration that Dmax is contrast limited over a wide range of pattern contrasts (722.5 %). Previous reports that Dmax is independent of density should be modified to take into account the complex effects of density upon the statistics of random patterns, and the existence of physiological filtering prior to motion detection.