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

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Abstract
The upper motion displacement threshold (D$_{\max}$) was determined with two-frame motion sequences of random binary luminance patterns, over a range of pattern element sizes and densities. D$_{\max}$ 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) D$_{\max}$ increased as element density was reduced in the range 50-5%. We explain our findings by a model which takes into account spatial-frequency filtering prior to motion detection, and the effects of pattern density upon the statistics of random binary patterns. We also implicate the dependence of D$_{\max}$ upon the contrast energy of the elements in broadband patterns, and provide a direct demonstration that D$_{\max}$ is contrast limited over a wide range of pattern contrasts (72-2.5%). Previous reports that D$_{\max}$ 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.