Unconscious inference

In perceptual psychology, unconscious inference (German: unbewusster Schluss), also referred to as unconscious conclusion,^[1] is a term coined in 1867 by the German physicist and polymath Hermann von Helmholtz to describe an involuntary, pre-rational and reflex-like mechanism which is part of the formation of visual impressions. While precursory notions have been identified in the writings of Thomas Hobbes, Robert Hooke, and Francis North^[2] (especially in connection with auditory perception) as well as in Francis Bacon's Novum Organum,^[3] Helmholtz's theory was long ignored or even dismissed by philosophy and psychology.^[4] It has since received new attention from modern research, and the work of recent scholars has approached Helmholtz's view.

In the third and final volume of his Handbuch der physiologischen Optik^[5] (1856–1867, translated as Treatise on Physiological Optics in 1920-1925, available here), Helmholtz discussed the psychological effects of visual perception. His first example is that of the illusion of the Sun rotating around the Earth:

Every evening apparently before our eyes the sun goes down behind the stationary horizon, although we are well aware that the sun is fixed and the horizon moves.^[6]