Much of the work regarding reinforcement began with behavioral psychologists such as Edward Thorndike, J. B. Watson and B.F. Skinner and their use of animal experiments. B.F. Skinner is famous for his work on reinforcement and believed that positive reinforcement is superior to punishment in shaping behavior. At first glance, punishment can seem like just the opposite of reinforcement, yet Skinner argued that they differ immensely; he claimed that positive reinforcement results in lasting behavioral modification (long-term) whereas punishment changes behavior only temporarily (short-term) and has many detrimental side-effects. Skinner defined reinforcement as creating situations that a person likes or removing a situation he doesn't like, and punishment as removing a situation a person likes or setting up one he doesn't like. Thus, the distinction was based mainly on the pleasant or aversive (unpleasant) nature of the stimulus.

Operant conditioning (or instrumental conditioning) is a type of learning in which an individual's behavior is modified by its consequences; the behaviour may change in form, frequency, or strength. Operant conditioning is a term that was coined by B. F. Skinner in 1937. The word operant refers to, "an item of behavior that is initially spontaneous, rather than a response to a prior stimulus, but whose consequences may reinforce or inhibit recurrence of that behavior".

Two other researchers, Azrin and Holz, expanded upon operant conditioning by focusing on the definition of punishment in their chapter to Honig’s volume on operant behavior, and they defined it as a “consequence of behavior that reduces the future probability of that behavior.” Skinner’s assumptions regarding reinforcement and punishment were thus challenged throughout the 1960s, and some studies have shown that positive reinforcement and punishment are equally effective in modifying behavior; that debate, however, continues in studies today as to whether or not reinforcement is more or equally as effective as punishment. Edward Thorndike also did some work regarding reinforcement in learning theory and believed that learning could occur unconsciously; that is, reinforcements or punishments could have an effect upon learning even if the person or organism is unaware of it. The research on the effects of positive and negative reinforcement alongside punishment continue today as those concepts apply directly to many forms of learning and behavior.

The basic definition is that a positive reinforcer adds a stimulus to increase or maintain frequency of a behavior while a negative reinforcer removes a stimulus to increase or maintain the frequency of the behavior. As mentioned above, positive and negative reinforcement are components of operant conditioning, along with positive punishment and negative punishment, all explained below:

Positive Reinforcement occurs when a stimulus is presented as a result of operant behavior and that behavior increases. Example: If a dog "sits" on command and this behavior is followed by the reward of a dog treat, then the dog treat serves to positively reinforce the behavior of "sitting."

Negative Reinforcement occurs when an aversive (unpleasant) stimulus is removed as a result of operant behavior and the rate of the behavior increases. Example: A child cleans his or her room, and this behavior is followed by the parent stopping "nagging" or asking the child repeatedly to do so. Here, the nagging serves to negatively reinforce the behavior of cleaning because the child wants to remove that aversive stimulus of nagging.

Positive punishment is the adding of an aversive (unpleasant) stimulus to decrease a behavior or response. Example: A mother yells at a child when he or she runs into the street. If the child stops running into the street, the yelling acts as positive punishment because the mother presents (adds) an unpleasant stimulus in the form of yelling.

Negative punishment is the removal of a pleasant stimulus to decrease a behavior or response. Example: A teenager comes home after curfew and the parents take away a privilege, such as cell phone usage. If the frequency of the child coming home late decreases, the removal of the phone is negative punishment because the parents are taking away a pleasant stimulus (the phone) and motivating the child to return home earlier.

See also:
http://en.wikipedia.org/wiki/Reinforcement
http://en.wikipedia.org/wiki/B._F._Skinner

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