p311fig08.30 The data of (Castet etal 1993) in the left image was simulated in the right image by the 3D FORMOTION model that I developed with my PhD student Jonathan Chey. These data provide insight into how feature tracking signals propagate from the ends of a line to its interior, where they capture consistent motion directional signals and inhibit inconsistent ones.<BR>||  Solving the aperture problem.  A key design problem: How do amplified feature tracking signals propagate within depth to select the cirrect motion directions at ambiguous positions?  This propagation from feature tracking signals to the line interior determines perceived speed in Castet etal data, which is why speed depends on line tilt and length. Data: (Castet etal 1993), Simulation: (Chey etal 1997)