Summary: The Visual System

The eyeball is circular because this is the best shape for gathering light into a focused image. The first few structures of the eye (the cornea, the lens, and the fluid filled chambers) serve the function of bending or refracting light. This helps bring light to a focus on the receptor surface-the retina-at the back of the eye. Nearsightedness (myopia) occurs when the focal plane is in front of the retina; farsightedness (hyperopia) occurs when the focal plane is in back of the retina. Corrective lenses change this. Rods (black and white receptors) and cones (color receptors) are found at the back of the retina.

Hallucinations and illusions show the difference between sensation and perception. The gestalt psychologists were fascinated with such demonstrations. Gestalt psychologists also pointed to the importance of the figure/ground distinction and other forms of evidence for central (brain) processes in perception.

Depth perception provides many examples of unconscious inference in the brain. Cues from the sensory information are used to draw conclusions about the distance of objects and surfaces. The problem of depth perception was recognized early in the study of perception: as scientists realized the brain had to extract depth information from an essentially two-dimensional surface (the back of the eye). Over time, scientists identified many depth cues that the brain uses to support the perception of three dimensions in our visual world.

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Copyright © 2007 Russ Dewey