A few months ago, a song got on my nerves. Too repetitive, too commercial, not my style. Then, quietly, it started playing on the radio, in cafés, in ads. Two weeks later, I caught myself humming it in the shower. It was not an artistic change of heart on my part. It was biology.

This phenomenon, known as the mere exposure effect, is one of the best-documented cognitive biases in social psychology. It says something fundamental about us: our brain confuses familiarity with quality. What is known feels reassuring. What is reassuring feels pleasant. And what is pleasant, we eventually come to like.

The experiment that changed everything

In 1968, American psychologist Robert B. Zajonc published a landmark paper: Attitudinal Effects of Mere Exposure, in the Journal of Personality and Social Psychology. The title is sober; the demonstration is astonishing.

In a series of experiments, Zajonc showed participants entirely neutral visual stimuli: Chinese characters, meaningless words supposedly of Turkish origin, and photographs of unfamiliar faces. These stimuli were shown at varying frequencies — some only once, others up to twenty-five times. He then asked participants to rate how “positive” or “pleasant” the stimuli seemed to them.

The result was clear: the more often a stimulus had been shown, the more favorably it was judged. And this happened regardless of any knowledge or understanding of the stimulus. Participants did not understand the Chinese characters and did not know what the Turkish words meant. But they liked them more. Simple repetition was enough.

“Familiarity does not breed contempt. It breeds affection.” — Robert B. Zajonc, 1968

What happens in the brain

Why does repetition produce affection? The answer lies in what neuroscience calls processing fluency. When we encounter something for the first time, our brain uses cognitive resources to analyze it: Is it a threat? Is it familiar? What does this signal mean?

On the second, third or tenth encounter, that work is far less intense. The stimulus is recognized quickly, without effort. And this feeling of ease — processing information without strain — is interpreted by the brain as a positive sign. The brain slides imperceptibly from “I recognize this without effort” to “I feel good facing this” to “I like this.”

This mechanism is probably very ancient. In an ancestral environment, what was familiar was generally safe: known territory, the faces of the tribe, plants already eaten. Novelty, by contrast, called for caution. Our brain kept that logic. It did not update it for the world of recommendation algorithms and advertising campaigns.

Advertising, politics, and us

The mere exposure effect is everywhere, and not always in harmless contexts.

Advertising relies heavily on this principle. It is not always about convincing you that the product is good: it is about making sure the name is present in your memory at the moment of purchase. Brands that spend fortunes on visibility are not necessarily trying to seduce you — they are trying to make you familiar. The rest follows.

In politics, studies have shown that simply repeating a candidate’s name — even when paired with neutral information — increases favorable evaluations. In 1974, an experiment by Richard Moreland and Robert Zajonc himself showed that students who attended a class more often tended to rate the professor more positively, independently of the course content. Presence is enough.

In our social relationships, this effect also plays a major role. Research on university friendships has repeatedly shown that physical proximity — sharing a residence hallway, working in the same open-plan office — is one of the strongest predictors of friendship. We bond with the people we see. Not necessarily with the people who suit us best on paper.

The limits: when too much is too much

The effect is not unlimited. Decades of research have confirmed it: beyond a certain exposure threshold, the curve reverses. This is called saturation, or more precisely habituation. The summer song, first made pleasant by repeated listening, eventually becomes irritating.

Several factors shape the saturation threshold:

• The complexity of the stimulus: complex objects (a rich musical work, a dense text) saturate less quickly than simple stimuli.
• The initial valence: if the first impression is clearly negative, repetition can sometimes amplify rejection rather than reduce it.
• The context of exposure: chosen exposure (you listen freely) saturates less quickly than imposed exposure (elevator music).

There is also an important distinction between conscious and subliminal repetition. Studies have shown that when we know we are being deliberately exposed to a stimulus to make us like it, the effect is reduced. The transparency of the manipulation changes something. But in real life, these exposures are rarely signaled as such.

What it says about us

This bias reveals an uncomfortable truth: a large share of our preferences are not really our own. They are the result of repeated exposures, often orchestrated by others, in contexts we are not aware of. The music we like, the brands we prefer, the people we appreciate — all of it is partly shaped by the simple number of times those stimuli have crossed our path.

That does not mean our tastes are false tastes. Familiarity can reveal real qualities we did not notice at first. But it is worth asking the question: do I really like this, or have I just seen it a lot?

The next time a logo, a political face or a melody suddenly seems likable for no clear reason, remember Zajonc and his Chinese characters. Your brain did not judge. It recognized. And it concluded that recognizing means liking.