What defines a stimulus change that can increase the future frequency of behavior without prior pairing with any other form of reinforcement?

An unconditioned reinforcer is defined as a stimulus that inherently has the ability to increase the future frequency of behavior without requiring prior learning or the process of pairing with other forms of reinforcement. These are typically biological and essential for survival, such as food, water, warmth, and comfort. Because unconditioned reinforcers are naturally effective, they can immediately influence behavior.

In contrast, conditioned reinforcers require some form of learning history or social context to be effective. They derive their reinforcing properties from being paired with unconditioned reinforcers or other established reinforcers. Generalized conditioned reinforcers also rely on prior conditioning but can be associated with multiple unconditioned reinforcers. Positive reinforcers increase the likelihood of a behavior occurring again but could include both unconditioned and conditioned reinforcers. Thus, the defining characteristic of the unconditioned reinforcer as an innate stimulus establishes its role in directly shaping behavior without prior associations.