Opponent process theory

The two processes

A stimulus triggers a primary response, the a-process, which closely follows the stimulus. A slower b-process opposes it. When the stimulus ends, the a-process stops quickly but the b-process lingers, leaving an opposite feeling for a while. Relief after a frightening event and the low following a pleasurable high would both be examples.

What repetition changes

With repeated exposure, the theory says the a-process stays roughly constant while the b-process grows larger and starts sooner. That yields a distinctive pattern, which Solomon used to explain acquired motives.

• Pleasure from a drug weakens with use, as tolerance develops
• Withdrawal after use becomes stronger and longer
• Activities that begin as frightening, such as parachuting, may come to deliver intense relief or exhilaration

Influence and limits

The theory influenced later accounts of addiction, including allostatic models of how reward systems shift with chronic drug use. It has been criticized for being difficult to test precisely, because the two processes are inferred from the net feeling rather than observed separately. Not all repeated experiences follow the predicted pattern, and accounts of addiction now give substantial weight to cue learning and incentive processes. A separate opponent process theory, in vision, concerns how the eye and brain code color and should not be confused with this one.