The after Effect of Seen Movement on a Plain Field

Abstract

Twenty laboratory subjects were asked to fixate the centre of a rotating spiral disc, under conditions where all of them, on stopping the disc, obtained the well known illusion of apparent expansion outwards. In this experiment, instead of stopping the disc, a completely uniform white surface was substituted and it was found that though the borders of the surface appeared to remain still, the surface itself showed apparent expansion in nearly all cases.