Association in psychology refers to a mental connection between concepts, events, or mental states that usually stems from specific experiences. Associations are seen throughout several schools of thought in psychology including behaviorism, associationism, psychoanalysis, social psychology, and structuralism. The idea stems from Plato and Aristotle, especially with regard to the succession of memories, and it was carried on by philosophers such as John Locke, David Hume, David Hartley, and James Mill. It finds its place in modern psychology in such areas as memory, learning, and the study of neural pathways. Association in psychology refers to a mental connection between concepts, events, or mental states that usually stems from specific experiences. Associations are seen throughout several schools of thought in psychology including behaviorism, associationism, psychoanalysis, social psychology, and structuralism. The idea stems from Plato and Aristotle, especially with regard to the succession of memories, and it was carried on by philosophers such as John Locke, David Hume, David Hartley, and James Mill. It finds its place in modern psychology in such areas as memory, learning, and the study of neural pathways. Associative learning is when a subject creates a relationship between stimuli (auditory or visual) or behavior (auditory or visual) and the original stimulus (auditory or visual). The acquisition of associations is the basis for learning. This learning is seen in classical and operant conditioning. Edward Thorndike did research in this area and developed the law of effect, where associations between a stimulus and response are affected by the consequence of the response. For example, behaviors increase in strength and/or frequency when they have been followed by reward. This occurs because of an association between the behavior and a mental representation of the reward (such as food). Conversely, receiving a negative consequence lowers the frequency of the behavior due to the negative association. An example of this would be a rat in a cage with a bar lever. If pressing the lever results in a food pellet, the rat will learn to press the lever to receive food. If pressing the lever resulted in an electric shock on the floor of the cage, the rat would learn to avoid pressing the lever. Classical conditioning is an example of a learned association. The classical conditioning process consists of four elements: unconditioned stimulus (UCS), unconditioned response (UCR), conditioned stimulus (CS), and conditioned response (CR). Without conditioning, there is already a relationship between the unconditioned stimulus and the unconditioned response. When a second stimulus is paired with the unconditioned stimulus, the response becomes associated with both stimuli. The secondary stimulus is known as the conditioned stimulus and elicits a conditioned response. The strength of the response to the conditioned stimulus increases over the period of learning, as the CS becomes associated with UCS. The strength of the response can diminish if CS is presented without UCS. In his famous experiment, Pavlov used the unconditioned response of dogs salivating at the sight of food (UCS), and paired the sound of a bell (CS) with receiving food, and later the dog salivated (CR) to the bell alone, indicating that an association had been established between the bell and food. In operant conditioning, behaviors are changed due to the experienced outcomes of those behaviors. Stimuli do not cause behavior, as in classical conditioning, but instead the associations are created between stimulus and consequence, as an extension by Thorndike on his Law of Effect. B.F. Skinner was well known for his studies of reinforcers on behavior. His studies included the aspect of contingency, which refers to the connection between a specific action and the following consequence or reinforcement. Skinner described three contingencies: positive reinforcement, negative reinforcement, and punishment. Reinforcements create a positive association between the action and consequence in order to promote the continuation of the action. This is done in one of two ways, positive reinforcers introduce a rewarding stimulus, whereas negative reinforcers remove an aversive stimulus to make the environment less aversive. Punishments create a negative relationship between the action and the consequence so that the action does not continue. Watson introduced a white fluffy rabbit to an infant, and created a connection between the rabbit and a loud noise. This experience for Little Albert associated a feeling of fear with the rabbit.