Perception (from the Latin perceptio, percipio) is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information.[1][2] All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs.[3] For example, vision involves light striking the retinas of the eyes, smell is mediated by odor molecules and hearing involves pressure waves. Perception is not the passive receipt of these signals, but can be shaped by learning, memory and expectation.[4][5] Perception involves these “top-down” effects as well as the “bottom-up” process of processing sensory input.[5] Perception depends on complex functions of the nervous system, but subjectively seems mostly effortless because this processing happens outside conscious awareness.[3]” – Source: