Reinforcement refers to any stimulus, event, or condition that, when contingent upon a behavioral response, increases the strength, frequency, or probability of that response occurring again. Unlike reward, which is a subjective state of pleasure or incentive, reinforcement is strictly defined by its functional effect on behavior.
- E.L. Thorndike's Law of Effect (1898): Posited that responses followed by satisfying states are more likely to recur, whereas those followed by discomfort are weakened. This formed the empirical bedrock for modern instrumental conditioning.
- B.F. Skinner's Operant Conditioning (1938): Expanded Thorndike's work using the operant chamber (Skinner Box). Skinner classified reinforcement into Positive Reinforcement (presentation of an appetitive stimulus) and Negative Reinforcement (removal of an aversive stimulus).
- Primary vs. Secondary Reinforcers: Primary reinforcers (e.g., food, water) possess innate biological value, while secondary or conditioned reinforcers (e.g., money, praise, tokens) acquire reinforcing properties through classical conditioning by being paired with primary reinforcers.
- Premack Principle (1965): David Premack proposed that a more valued, highly probable behavior can act as a reinforcer for a less valued, lower probability behavior (e.g., "After you finish your homework [low probability], you can play video games [high probability]").