Phenomenal Rarefaction and Visual Acuity under ‘Illusory’ Conditions

Given a striped pattern, there are two ways of obtaining a phenomenal rarefaction of it: (a) by reducing the area of the pattern, leaving the distance between the stripes unchanged, or (b) by placing the pattern within one of Delboeuf's illusion contexts. With (a) phenomenal rarefaction is coupled with an increment of visual acuity, since the stripes are distinctly seen at a greater distance. With (b) the phenomenal rarefaction is the same as with (a), but is not associated with any increase of visual acuity. The rôle of ‘actual’ and ‘illusory’ conditions on visual perception is discussed.