Habituation

Habituation is a form of non-associative learning in which an organism's response to a stimulus weakens after repeated or prolonged exposure. Nothing is paired with anything — the organism simply learns that the stimulus carries no consequence and stops reacting. A person who moves next to train tracks initially startles at every passing train, then within weeks barely notices the noise.

Two contrasts sharpen the definition. Habituation is the opposite of sensitization, in which repeated exposure — typically to an intense or threatening stimulus — amplifies the response instead of dampening it. And habituation is distinct from sensory adaptation: adaptation happens at the level of sensory receptors becoming less responsive, while habituation is a change in behavior that occurs even when the senses still register the stimulus. A related phenomenon, dishabituation, is the recovery of a habituated response when the stimulus changes or a new stimulus intervenes.

Habituation matters because attention is limited. Filtering out constant, meaningless input frees cognitive resources for novel or significant events, which is why habituation appears in virtually every species studied — from sea slugs to humans — and why infant researchers use looking-time habituation to test what babies perceive as new.

Both the MCAT and AP Psychology exams test habituation within their learning units — expect questions distinguishing it from sensitization, from sensory adaptation, and from associative forms of learning like classical and operant conditioning.