The Münsterberg illusion and 'irradiation'

The Münsterberg illusion is a compelling phenomenon for which there is no generally accepted explanation. It is suggested that two different contour-shifting effects operate in this illusion, and these are named the 'symmetrical effect' and the 'corner effect' respectively. It is further suggested that both of these effects are caused by 'irradiation', and an attempt is made to cast some light upon the phenomenon of irradiation, which is itself only poorly understood.