camera obscura a darkened enclosure that focuses light from an external object by a pinpoint hole instead of a lens, creating an inverted, reversed image on the opposite wall. The adoption of the camera obscura as a model for the eye revolutionized the study of visual perception by rendering obsolete previous speculative philosophical theories, in particular the emanation theory, which explained perception as due to emanated copy-images of objects entering the eye, and theories that located the image of perception in the lens rather than the retina. By shifting the location of sensation to a projection on the retina, the camera obscura doctrine helped support the distinction of primary and secondary sense qualities, undermining the medieval realist view of perception and moving toward the idea that consciousness is radically split off from the world. See also PERCEPTIO. T.H.L.