The functional architecture of human visual motion perception.

UNLABELLED: A powerful paradigm (the pedestal-plus-test display) is combined with several subsidiary paradigms (interocular presentation, stimulus superpositions with varying phases, and attentional manipulations) to determine the functional architecture of visual motion perception: i.e. the nature of the various mechanisms of motion perception and their relations to each other. Three systems are isolated: a first-order system that uses a primitive motion energy computation to extract motion from moving luminance modulations; a second-order system that uses motion energy to extract motion from moving texture-contrast modulations; and a third-order system that tracks features. Pedestal displays exclude feature-tracking and thereby yield pure measures of the first- and second-order systems which are found to be exclusively monocular. Interocular displays exclude the first- and second-order systems and thereby to yield pure measures of feature-tracking.
RESULTS: both first- and second-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 requires much more stimulus contrast than the first- and second-order systems. Feature tracking is both bottom-up (it computes motion from luminance modulation, texture-contrast modulation, depth modulation, motion modulation, flicker modulation, and from other types of stimuli) and top-down--e.g. attentional instructions can determine the direction of perceived motion.