Matched filtering in motion detection and discrimination

When humans detect and discriminate visual motion, some neural mechanism ex tracts the motion information that is embedded in the noisy spatio-temporal stimulus. We show that an ideal mechanism in a motion discrimination exper iment cross-correlates the received waveform with the signals to be discrim inated. If the human visual system uses such a cross-correlator mechanism, discrimination performance should depend on the cross-correlation between t he two signals. Manipulations of the signals' cross-correlation using diffe rences in the speed and phase of moving gratings produced the predicted cha nges in the performance of human observers. The cross-correlator's motion p erformance improves linearly as contrast increases and human performance is similar. The ideal cross-correlator can be implemented by passing the stim ulus through linear spatio-temporal filters matched to the signals. We prop ose that directionally selective simple cells in the striate cortex serve a s matched filters during motion detection and discrimination.