p108fig03.28 The watercolor illusion of Baingio Pinna 1987 can be explained using spatial competition betweeen like-oriented boundary signals.  This occurs at what I have called the First Competitive Stage.  This is one stage in the brain's computation of hypercomplex cells, which are also called endstopped complex cells.  Why the blue regions seem to bulge in depth  may be explained using multple-scale, depth-selective boundary webs.  See ther text for details.<BR>|| Baigio Pinna. <I>Watercolor illusion 1987</i>. Filled-in regions bulge in depth.  Multiple-scale, depth-selective boundary web!