R.O. Dror, D.C. O'Carroll, and S.B. Laughlin. Accuracy of velocity estimation by Reichardt correlators. Journal of the Optical Society of America A 18:241-252, 2001.
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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 realistic Reichardt correlators can provide velocity estimates in an organism's natural visual environment. 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. Analysis and simulations suggest that processes commonly found in visual systems, such as prefiltering, response compression, integration and adaptation, improve the reliability of velocity estimation and expand the range of velocities coded. Experimental recordings confirm our predictions of correlator response to broad-band images.