(Physiol.) An impression, or the consciousness of an impression, made upon the central nervous organ, through the medium of a sensory or afferent nerve or one of the organs of sense; a feeling, or state of consciousness, whether agreeable or disagreeable, produced either by an external object (stimulus), or by some change in the internal state of the body. "Perception is only a special kind of knowledge, and sensation a special kind of feeling.... Knowledge and feeling, perception and sensation, though always coexistent, are always in the inverse ratio of each other."