John B. Watson, answered from the texts and cited to the page.
Stimulus and response are the two terms on which the whole of a scientific psychology turns. Strip away every mentalistic word — sensation, perception, desire, image — and what you have left, what you can actually observe and measure, is an organism doing something in response to something that happened.1 A stimulus is any object in the general environment, or any change in the tissues of the body itself due to its physiological condition.2
The examples are plain enough: flash a strong light in your eye and the pupil contracts; fire a pistol behind a man's head and he jumps; release hydrogen sulphide in a room and every person in it moves toward the door.3 But do not make the mistake of thinking the stimulus is always external. The muscles of your stomach contract rhythmically before dinner because food is absent; pressure of certain fluids in the male leads to sex activity; the very tension of a contracting muscle generates a stimulus that calls out a further response in that same muscle or in one at a distance.4
The organism is, at every moment, assailed from without and from within simultaneously.5 A response is anything the animal does — turning toward or away from a light, jumping at a sound, and equally: building a skyscraper, drawing plans, writing books.6 Saying is doing; speaking overtly or to ourselves is as objective a type of behavior as baseball.7
The goal, then, is this: given the stimulus, predict the response; given the response, name the stimulus that caused it.8 Everything else in psychology — habit, emotion, personality, thought — is built on top of that relation, or it is nothing a science can touch.
He dropped from his scientific vocabulary all subjective terms such as sensation, perception, image, desire, purpose, and even thinking and emotion as they were subjectively defined.The Ways of Behaviorism
By stimulus we mean any object in the general environment or any change in the tissues themselves due to the physiological condition of the animal.The Ways of Behaviorism
If I suddenly flash a strong light in your eye, your pupil will contract rapidly... If a pistol shot were suddenly fired in the back part of the room, practically all of you would jump... If hydrogen sulphide were suddenly released in the room you would begin to hold your noses and possibly even seek to leave the room.The Ways of Behaviorism
Just before dinner tonight the muscles of your stomach began to contract and expand rhythmically because of the absence of food... the muscle is under constant tension; any increase in that tension, as when a movement is made, gives rise to a stimulus which leads to another response in that same muscle or in one in some distant part of the body.The Ways of Behaviorism
So we see that the organism is constantly assailed by stimuli—which come through the eye, the ear, the nose and the mouth... at the same time the inside of our body is likewise assailed at every movement by stimuli arising from changes in the tissues themselves.The Ways of Behaviorism
By response we mean anything the animal does—such as turning towards or away from a light, jumping at a sound, and more highly organized activities such as building a skyscraper, drawing plans, having babies, writing books, and the like.The Ways of Behaviorism
saying is doing—that is, behaving. Speaking overtly or to ourselves (thinking) is just as objective a type of behavior as baseball.The Ways of Behaviorism
the goal of psychological study is the ascertaining of such data and laws that, given the stimulus, psychology can predict what the response will be; or, on the other hand, given the response, it can specify the nature of the effective stimulus.Psychology from the Standpoint of a Behaviorist