CONVERGENCE MICROPSIA

   Also referred to as accommodative micropsia, accommodation-convergence micropsia, and oculomotor micropsia. All three terms are used to denote a type of * micropsia (i.e. the visual perception of an object or stimulus that is apparently decreased in size) due to convergence and accommodation of the eyes, as may occur in squinting, for example. The process of reducing the apparent size of objects and stimuli is called *minification. The British scientist and inventor Charles Wheat-stone (1802-1875) has been credited with being the first to report on convergence micropsia avant la lettre in 1852.The term accommodative micropsia appears in the 1939 Text-book of Ophthalmology by the Scottish ophthalmologist Sir Stewart Duke-Elder (1899-1978). Experimental research suggests that this physiological type of micropsia is due mainly to convergence, and only to a lesser extent to accommodation of the eyes. Additional mechanisms that may play a part in the mediation of convergence microp-sia, albeit to an even lesser extent, are the pinhole effect (i.e. in cases where an object is observed through a pinhole), the shift in the position of the nodal point of the eye while it accommodates, and perhaps a central mechanism connected with the * corollary discharge signal coinciding with accommodation. Convergence micropsia is classified as a *physiological illusion.

   References

   Duke-Elder, W.S. (1939). Text-book of ophthalmology, Volume 1. Saint Louis, MO: C.V. Mosby Company.

   Hollins, M. (1976). Does accommodative micropsia exist? American Journal of Psychology, 89, 443-454.

   Wheatstone, C. (1852). The Bakerian lecture: Contributions to the physiology ofvision; Part the second, On some remarkable, and hitherto unobserved, phenomena of binocular vision (continued). Philosophical Magazine,4th ser. 3, 504-523.