R.O. Dror, D.C. O'Carroll, and S.B. Laughlin. The role of natural image statistics in biological motion estimation.  IEEE International Workshop on Biologically Motivated Computer Vision.  Springer Lecture Notes in Computer Science 1811:492-501, 2000. 
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Abstract

While a great deal of experimental evidence supports the Reichardt correlator as a mechanism for biological motion detection, the correlator does not signal true image velocity. This study examines the accuracy with which physiological Reichardt correlators can provide velocity estimates in an organism's natural visual environment. Both simulations and analysis show that the predictable statistics of natural images imply a consistent correspondence between mean correlator response and velocity, allowing the otherwise ambiguous Reichardt correlator to act as a practical velocity estimator. A computer vision system may likewise be able to take advantage of natural image statistics to achieve superior performance in real-world settings.