THE FUNCTIONAL ARCHITECTURE OF HUMAN VISUAL-MOTION PERCEPTION

A powerful paradigm (the pedestal-plus-test display) is combined with several subsidiary paradigms (interocular presentation, stimulus super positions with varying phases, and attentional manipulations) to deter mine the functional architecture of visual motion perception: i.e. the nature of the various mechanisms of motion perception and their relat ions to each other. Three systems are isolated: a first-order system t hat uses a primitive motion energy computation to extract motion from moving luminance modulations; a second-order system that uses motion e nergy to extract motion from moving texture-contrast modulations; and a third-order system that tracks features. Pedestal displays exclude f eature-tracking and thereby yield pure measures of the first- and seco nd-order systems which are found to be exclusively monocular. Interocu lar displays exclude the first- and second-order systems and thereby t o yield pure measures of feature-tracking. Results: both first- and se cond-order systems are fast (with temporal frequency cutoff at 12 Hz) and sensitive, Feature tracking operates interocularly almost as well as monocularly. It is slower (cutoff frequency is 3 Hz) and it require s much more stimulus contrast than the first- and second-order systems . Feature tracking is both bottom-up (it computes motion from luminanc e modulation, texture-contrast modulation, depth modulation, motion mo dulation, flicker modulation, and from other types of stimuli) and top -down-e.g. attentional instructions can determine the direction of per ceived motion.