Perception is the
organization, identification, and interpretation of sensory information in
order to represent and understand the environment. All perception involves
signals in the nervous system, which in turn result from physical or chemical
stimulation of the sense organs. For example, vision involves light striking
the retina of the eye, smell is mediated by odor molecules, and hearing
involves pressure waves. Perception is not the passive receipt of these signals,
but is shaped by learning, memory, expectation, and attention.