Pe****tion (from the Latin pe****tio, percipio) is the organization, identification, and interpretation of sensory information in order to represent and understand the environment. All pe****tion 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. Pe****tion is not the passive receipt of these signals, but is shaped by learning, memory, expectation, and attention.