2ND-ORDER MOTIONS CONTRIBUTE TO VECTION

First- and second-order motions differ in their ability to induce moti on aftereffects (MAEs) and the kinetic depth effect (KDE). To test whe ther second-order stimuli support computations relating to motion-in-d epth we examined the vection illusion (illusory self motion induced by image flow) using a vection stimulus (V, expanding concentric rings) that depicted a linear path through a circular tunnel. The set of vect ion stimuli contained differing amounts of first- and second-order mot ion energy (ME). Subjects reported the duration of the perceived MAEs and the duration of their vection percept. Tn Experiment 1 both MAEs a nd vection durations were longest when the first-order (Fourier) compo nents of V were present in the stimulus. In Experiment 2, V was multip licatively combined with static noise carriers having different check sizes. The amount of first-order ME associated with V increases with c heck size. MAEs were found to increase with check size bur vection dur ations were unaffected. In general MAEs depend on the amount of first- order ME present in the signal. Vection, on the other hand, appears to depend on a representation of image flow that combines first- and sec ond-order ME. (C) 1998 Elsevier Science S.A. All rights reserved.