Individuals operate in his or her environment to produce a change in it. It was B. F. Skinner who proposed the theory of operant learning in his quest to study directly observable behaviors. He conducted a series of experiments with rats. An animal was placed in the 'Skinner box'. It was expected to press a lever in the box to receive a pellet of food. After exploring its environment, the rat learned to make the response that would deliver food. Another experiment involved the rat learning to press the lever in order to avoid receiving an electrical shock.
An organism is said to 'operate' or make specific voluntary responses in a certain environment in order to produce a change in it. This theory is also called 'instrumental learning' because an organism and the specific behavior are both instrumental in producing the subsequent change. Simply put, people learn to act in ways determined by the outcome that follows their action. If a specific behavior is followed by a desirable outcome, that behavior is likely to occur again, because it is 'reinforced'. A response followed by something undesirable is unlikely to occur again. Thus, a reinforcer is something that increases the occurrence of the behavior it follows.
It is notable that the avoidance of something can also work in the reinforcement of a response, and is thus considered a reinforcer. When you wear your seat belt, you're acting to avoid or terminate negative stimuli, such as the beeping noise. There are many instances in our life when we act in a certain way to avoid something unpleasant. These examples bring forth the positive and negative nature of reinforcers and the reinforcement they produce.
You receive good grades on a test and are praised. You prepare well the next time to keep those grades up. You score poorly on a test and are sternly reprimanded. You study well the next time to avoid receiving another bad grade. The response of studying for the test is reinforced in both scenarios. However, it is the events that reinforce it that create the distinction between positive and negative reinforcement. In the former scenario, receiving praise acts as a stimulus that strengthens that behavior. The latter involves the avoidance of reprimands acting as the stimulus that reinforces studying.
Positive reinforcement involves the delivery or presentation of a desirable stimulus after a response, thus reinforcing it. Negative reinforcement involves the termination or removal of an undesirable stimulus after a response, which reinforces it. In the case of reinforcement of behavior, the outcome of that particular response is generally considered 'pleasant', regardless of whether it is positively or negatively reinforced. The removal of a negative stimulus is pleasant, after all, and thus works in making the response preceding it more likely to be repeated. Playing music to end boredom is another example. The elimination of boredom serves to reinforce it. Negative reinforcement studies also relate to escape and avoidance conditioning, such as wearing a sweater to avoid feeling cold.
The terms positive and negative reinforcement are simply indicators of the introduction or removal of a certain stimulus. They must not be assumed as being 'good' or 'bad' due to their semantic connotations.
It is common to confuse the terms 'negative reinforcement' and 'punishment'. Punishment functions as an antithesis of reinforcement, as it serves to decrease the tendency of a behavior. Thus, any response followed by a punishing stimulus is less likely to be repeated. However, "negative" in this context is simply the termination of a stimulus. Like reinforcement, punishment includes both positive and negative punishment. Positive punishment introduces an aversive stimulus to reduce a response. Negative punishment is the termination of a desirable stimulus to reduce a response. Both reinforcement and punishment involve the introduction or removal of certain stimuli, but serve to fulfill opposite functions.