From The Art and Popular Culture Encyclopedia
In psychology, stimuli are energy patterns (e.g. light or sound) which are registered by the senses. In behaviorism and related stimulus–response theories, stimuli constitute the basis for behavior, whereas in perceptual psychology they constitute the basis for perception.
In the second half of the 19th century, the conception had been established by psychophysics, the "scientific study of the relation between stimulus and sensation", together with the notion of the reflex arc constituting a foundational concept of scientific psychology. While at this time "whatever could be controlled by an experimenter and applied to an observer could be thought of as a stimulus." In the context of perception, a distinction is made between the distal stimulus (the external, perceived object) and the proximal stimulus (the stimulation of sensory organs).