Opponent process theory is actually two different theories in psychology that share the same core idea: the brain responds to stimulation by generating an opposite reaction. One version explains how you see color. The other explains how emotions and motivation work, particularly in addiction. Both are foundational concepts, and understanding the difference matters.
The Two Versions at a Glance
The color vision version, proposed by physiologist Ewald Hering in the 19th century, explains why you perceive certain colors the way you do. The motivational version, introduced by psychologist Richard Solomon in 1974, explains why intense emotional experiences produce a rebound in the opposite direction, like the rush of relief after something terrifying ends. They operate on the same principle (opposing processes in the nervous system) but apply to completely different domains.
Color Vision: Why You Never See Reddish Green
Hering noticed something peculiar about color perception: you can imagine a reddish yellow (orange) or a bluish green (turquoise), but you cannot imagine a reddish green or a bluish yellow. Those combinations simply don’t exist in human experience. He proposed that the visual system processes color through three antagonistic channels: red versus green, blue versus yellow, and black versus white. Each pair works like a seesaw. When one side is active, it suppresses the other.
This is why staring at a red square for 30 seconds and then looking at a white wall produces a green afterimage. The red side of the channel fatigues, and the green side temporarily dominates. Hering proposed that specific neurons respond in qualitatively different ways to light of different wavelengths, firing in one direction for red and the opposite direction for green. Modern neuroscience has confirmed this. Cells in the visual pathway do behave as opponent channels, validating what Hering theorized from pure observation over a century ago.
Motivation and Emotion: The A-Process and B-Process
Richard Solomon’s 1974 theory applies the same logic to feelings. He proposed that any strong emotional state automatically triggers an opposing reaction from the nervous system. The initial feeling is the “a-process,” and the brain’s counterresponse is the “b-process.” The net experience you feel at any moment is the combination of the two.
Here’s how it plays out in real time. When something pleasurable happens, the a-process fires quickly and produces a strong positive feeling. Shortly after, the b-process kicks in to dampen that pleasure, pulling your emotional state back toward neutral. When the pleasurable stimulus stops, the a-process shuts off immediately, but the slower b-process lingers. That lingering opposite feeling is what you experience as a crash, a comedown, or a sense of loss after something enjoyable ends.
The reverse works for negative experiences. A painful or frightening event triggers an intensely negative a-process, followed by a positive b-process that builds more slowly. When the fear or pain ends, the negative a-process vanishes, but the positive b-process keeps going for a while, producing relief, exhilaration, or even euphoria.
Skydiving: The Classic Example
Solomon used skydiving to illustrate the theory, and researchers have since tested it directly. Novice skydivers experience intense anxiety before and during their first jump. But after landing safely, many report a powerful emotional high. Some novice jumpers feel this euphoria for a week or more after their first jump. The a-process (terror) ends abruptly on landing, but the b-process (relief and elation) continues without opposition.
Experienced skydivers show a different pattern. A study comparing 29 novices with 34 experienced jumpers found that veterans experience far less emotional contrast from pre-jump to post-jump. They’re more emotionally stable throughout. This fits Solomon’s prediction perfectly: with repeated exposure, the a-process weakens while the b-process strengthens. Veteran jumpers feel less fear before the jump and less euphoria after it. Their emotional experience flattens out over time.
How the Theory Explains Addiction
The most influential application of opponent process theory is in understanding how addiction develops. The progression follows a predictable sequence that maps directly onto the a-process and b-process dynamic.
When someone first uses an addictive substance, the a-process produces a strong pleasurable effect. The brain’s reward circuitry activates rapidly, flooding key pathways with dopamine. The b-process, which opposes that pleasure, is initially weak and slow. So the person experiences a strong high followed by a mild comedown. This is the initiation stage, driven by positive reinforcement: the drug feels good.
With repeated use over weeks, the system adapts. The a-process (pleasure) becomes desensitized while the b-process (the opposing negative state) becomes sensitized. This creates tolerance: the same dose produces less pleasure because the opposing process has grown stronger and faster. The person needs more of the substance to get the same effect.
This leads to what researchers call the maintenance stage. The person is no longer chasing the original high so much as trying to avoid the increasingly unpleasant withdrawal state. The b-process, now powerful from repeated activation, produces sustained negative feelings whenever the substance wears off. Taking the drug becomes less about feeling good and more about not feeling terrible. The motivation shifts from positive reinforcement to negative reinforcement.
When someone stops using the substance entirely, the withdrawal stage begins. The a-process is no longer being triggered, but the enlarged b-process continues to operate, producing persistent negative mood that can last days to weeks before the system recalibrates. This sustained negative state is what makes quitting so difficult and relapse so common.
The Shifting Emotional Baseline
One of the theory’s most important insights is that repeated exposure to a stimulus doesn’t just change how you respond to it. It changes your baseline emotional state. Under normal conditions, the brain operates within a homeostatic range, returning to a relatively stable emotional set point after any disturbance. But when the b-process is strengthened by chronic use, it doesn’t fully return to its original level between exposures. The set point itself drifts.
This is what addiction researchers call allostasis: a new, abnormal equilibrium where the brain’s reward system is chronically suppressed. The person’s “normal” now feels worse than their original normal. The reward circuitry isn’t broken in a simple way. Rather, the opposing process has grown so dominant that it suppresses the brain’s feel-good signaling even in the absence of the substance. This shift is fueled not only by changes in reward circuits but also by the activation of the body’s hormonal stress responses, compounding the negative state.
What Happens in the Brain
At the biological level, the a-process and b-process correspond to real, measurable changes. The initial rewarding effect of substances like opiates works by releasing dopamine in the brain’s reward pathways. This dopamine surge is the a-process in neurochemical terms, and it operates on a timescale of hours.
The b-process involves slower physiological adaptations. Research on opiate withdrawal has shown that anxiety during withdrawal results from a drop in activity at the same receptors that produced the original high, leading to a corresponding loss of dopamine signaling. The body also makes structural adjustments: glands that regulate stress hormones physically change in size over weeks of substance use, creating a slow-building oppositional process that operates on a timescale of days to weeks. These physical changes are part of why withdrawal is not just psychological but deeply physiological.
Beyond Addiction
While addiction is the most studied application, opponent process theory applies to any intense emotional experience that repeats. The runner who initially dreads a morning jog but eventually craves it is experiencing the same dynamic: the negative a-process (discomfort) weakens with practice while the positive b-process (the runner’s high and post-exercise calm) strengthens. The same logic applies to sauna use, cold water immersion, spicy food enjoyment, and even the attachment patterns in close relationships, where the pleasure of a partner’s presence is matched by the pain of their absence.
Solomon’s original framework was deliberately broad. He argued that the central nervous system automatically opposes any strong hedonic state, whether pleasant or aversive, and that these opponent processes are strengthened by use and weakened by disuse. That single principle generates predictions across an enormous range of human behavior, from why thrill-seekers escalate to more extreme activities, to why the absence of a loved one hurts more the longer the relationship has lasted.