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Matched filtering in motion detection and discrimination

When humans detect and discriminate visual motion, some neural mechanism extracts the motion information that is embedded in the noisy spatio–temporal stimulus. We show that an ideal mechanism in a motion discrimination experiment cross–correlates the received waveform with the signals to be discriminated. If the human visual system uses such a cross–correlator mechanism, discrimination performance should depend on the cross–correlation between the two signals. Manipulations of the signals' cross–correlation using differences in the speed and phase of moving gratings produced the predicted changes in the performance of human observers. The cross–correlator's motion performance improves linearly as contrast increases and human performance is similar. The ideal cross–correlator can be implemented by passing the stimulus through linear spatio–temporal filters matched to the signals. We propose that directionally selective simple cells in the striate cortex serve as matched filters during motion detection and discrimination.