"There are no sights, sounds, tastes, or smells in the world--just various types of waves and molecules. Sensations, therefore, are 'virtual' constructs created by the brain. The sense organs begin this extraordinary act of transformation by turning stimuli, such as light waves or the touch of certain molecules, into electrical signals that are carried to brain areas dedicated to dealing with that type of input. Some stimuli also originate from within the rest of the body. Although some sensations are consciously experienced, many remain unconscious. 

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From The Brain, by Rita Carter