Visual motion of missing-fundamental patterns: motion energy versus feature correspondence

Missing-fundamental gratings, generated by subtracting the fundamental Four ier components from square-wave gratings, appear to move backward when pres ented in quarter-cycle jumps, even though their edges and features all move forward. We used variants of these stimuli to test current models of motio n perception. We found that missing-fundamental plaids, constructed from or thogonal missing-fundamental gratings, also appear to move backward. Forwar d motion was restored to missing-fundamental gratings and plaids by adding back small fractions of the original fundamental. In-phase and antiphase ad dition of the fundamental had similar effects on the perceived motion, desp ite having markedly different effects on the features, appearances and zero -crossings of the stimuli. The critical amplitude of fundamental needed to restore forward motion to plaids was the same as that needed to restore for ward motion to their isolated component gratings, indicating that the plaid s' emergent features, such as edge intersections and 'blobs', made little o r no contribution to the perceived direction of motion in these stimuli. In two derivative experiments, missing-fundamental chromatic gratings and pla ids, at approximate isoluminance, and missing-fundamental luminance barberp oles, also generated backward perceived motions, and these were also revers ed by in-phase or antiphase addition of small amounts of fundamental. (C) 2 000 Elsevier Science Ltd. All rights reserved.