p093fig03.06 Every line is an illusion because regions of the line that are occluded by the blind spot or retinal veins are completed at higher levels of brain processing by boundary completion and surface filling-in. <BR>|| Every line is an illusion!<TABLE border="1"><TR><TD>Boundary completion</td><TD>Which boundaries to connect?</td></tr><TR><TD>Surface filling-in</td><TD>What color and brightness do we see?</td></tr></table>