A neural model of high-level motion processing: line motion and formotion dynamics.

The percepts known variously as the line motion illusion, motion induction, and transformational apparent motion have attracted a great deal of experimental interest, since they sensitively probe interactions between preattentive and attentive vision processes. The present article develops a neural model that qualitatively explains essentially all the data reported thus far, and quantitatively simulates key illustrative percepts. The model suggests how these data arise from neural mechanisms of preattentive boundary and surface formation, long-range apparent motion, formotion interactions, and spatial attention. The boundary and surface formation processes model aspects of the interblob V1-->interstripe V2-->V4 and blob V1-->thin stripe V2-->V4 cortical processing streams, respectively. The long-range apparent motion process models aspects of the V1-->MT-->MST processing stream. An interstream V2-->MT form-motion interaction is proposed to allow the motion processing stream to track transient properties of emergent boundaries and filled-in surface colors from the form processing stream. It does so by generating motion waves using the long-range apparent motion process. This interstream interaction controls the formation of form-motion percepts, which are herein called formotion percepts. Other transients directly cause motion waves within the motion processing stream. All the data are attributed to properties of such motion waves. It is also suggested how bottom-up motion mechanisms can engage top-down attention as part of the motion capture process that solves the aperture problem. This interaction is proposed to occur between areas MT and MST. The model hereby explains how attention can be engaged even in percepts whose explanation can be derived from preattentive mechanisms.