The phenomenon of seeing one's own blind spots as afterimages and its implication for the cortical origin of afterimages

Charles Q. Wu

Abstract:

Each of our eyes is "endowed" with a blind spot (BS). Normally one does not see them, but under suitable conditions one can indeed see one or both of their BSes. More intriguingly, the BSes can manifest themselves as complementary afterimages (AIs). This phenomenon of seeing one’s own BSes as AIs was first described by Charpentier (1898) and subsequently reported by many others [as reviewed by Helson (1934)]. In a dark room, with one eye open and other shadowed, one adapts to a uniformly illuminated background (e.g., a LED red light at 5 lux; a screen with 50% reflectance) for 10 minutes; upon suddenly closing the eye, they will see a bluish-green (i.e., complementary color to red) spot corresponding to the BS of the viewing eye. Now I demonstrate an important implication of this phenomenon regarding the retinal versus cortical origin of AIs: Since there are neither photoreceptors for the BS in retina, nor cells representing BS within the LGN (lateral geniculate nucleus), this phenomenon implies that the origin of AIs is cortical; furthermore, relating this phenomenon to
the neuroanatomical study of the human primary visual cortex (cortical area V1) by Adams and Horton (2002), we can infer that AIs originate in layer 4 of V1.