Figure 1. The Central Problem of Vision.

The problem is twofold: one component is optical and the other biological. The optical problem involves reflection of light off of surfaces in the visual environment. This light is refracted by the crystalline lens at the front of the eye, resulting in a pattern of light (the retinal image) that is projected and focused on the retinal surface at the back of the eye. The biological problem–the problem of perception–involves identification of the elements of the visual scene that gave rise to the retinal image. This is a classic inverse problem for which there is no unique solution: a given retinal image could be caused by any one of an infinite set of visual scenes.

This fundamental ambiguity is not reflected in human perceptual experience, however, for we generally arrive quickly at a solution and the chosen solution is nearly always correct (in that it reflects the “true” environment). This is only possible by using other sources of information, including the spatial relationships between different features of the image (spatial context), the observer’s prior experiences (temporal context), and consistent properties of the visual world (for example, that light comes from above) that have become embedded in the computational machinery of the brain through natural selection (evolutionary context). Recent experiments summarized herein have revealed much about how these contextual influences enable perception. Source: Figure prepared by author.