We investigate processes of the eye and brain that serve vision. Most of the research focuses on visual pathways that mediate color and brightness perception. While color and brightness of an isolated light are closely related to the light's physical properties -- its energy and wavelengths -- this is a misleading fact for understanding normal viewing. The color and brightness of a light in a complex scene are not directly related to the light's physical features. Two examples are below.

The 6 horizontal bars above are	     How many different background lights
identical physically but appear	     are in the 16 squares above?  Answer:  4.
unequal.  The surrounding light	     The background light in each column, from 
alters the neural signals that       top to bottom, is the same.  The grid lines
mediate brightness perception.	     alter the color of background that we perceive.

  Color and brightness are not in light. What we see depends directly on a pattern of neural responses, not on the wavelength or energy of light that enters the eye. The simple relation between a physical stimulus and how we perceive it breaks down when the light is part of a complex scene. In natural viewing, the whole visual stimulus is a patchwork of different lights from many objects. The neural response to a particular light, and therefore our perception of it, is affected by the context of the other lights also in view.

  The neural processes that mediate color and brightness are studied in psychophysical experiments in which human observers judge the appearance of lights presented in the context of other visual stimuli. Specific theories of neural processing in eye and brain are developed and tested with the results from these experiments.

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