Robert Zajonc first published his findings on the mere exposure effect in 1968. In an article titled “Attitudinal Effects of Mere Exposure,” he described a series of experimental findings that fundamentally challenged the psychological understanding of preferences accepted at the time.

According to that understanding, preferences were a result of conscious thinking. Cognitions were believed to come first, in the form of information processing, evaluation, and inferences about a perceived object.

Attitudes, in the form of likes, dislikes, and preferences among alternatives were believed to form only later, based on those prior cognitive processes. In other words, you had to think about something before you could form a preference regarding it.

Zajonc turned this model on its head. In his most famous experiment, he had volunteers view a long series of simulated Chinese ideograms (mostly nonsense symbols in the style of real Chinese ideograms).

Some symbols were shown only once, others up to five times. Participants were then asked to guess whether the symbols represented positive or negative words.

Overwhelmingly, the more exposures of a symbol people saw, the more “positive” they rated it. Since the symbols were completely novel and meaningless, there was no way for information processing to precede preference formation. This was the first demonstration of the mere exposure effect.

Zajonc showed that people could develop preferences for things based on repetition of exposure alone, without any prior information processing or evaluation; indeed, without even knowing their preferences were being influenced by exposure frequency.¹

Later studies by Zajonc and others demonstrated that the mere exposure effect was powerful and ubiquitous, occurring with words, numbers, faces, works of art, music, interpersonal interactions, and many other types of stimuli.² It has come to be seen as one of the most consistent and persistent psychological phenomena ever discovered.

To settle conclusively the question of whether conscious thoughts might be slipping in as a source of the mere exposure effect, Zajonc began to explore whether stimuli experienced below the threshold of conscious awareness, that is, subliminal stimuli, could induce liking based on frequency alone.

Using new display technologies that started becoming available in the 1970s, Zajonc began testing subjects with stimuli presented for as little as one-thousandth of a second (one millisecond).

He found that preferences not only increased for more frequently presented subliminal stimuli, despite the fact that people were unaware of having “seen” them, but even more significantly, he found that the effect was stronger for subliminally presented stimuli compared to consciously perceived stimuli.

These findings established in very strong terms the validity of Zajonc’s original hypothesis: changes in preferences induced by repeated exposures depended not on any prior subjective and conscious evaluations of attributes of the stimulus, but rather resulted from the objective history of exposures alone.³

When derived from mere exposure, preferences indeed need no inferences.

Mere Exposure and Classical Conditioning

Much effort has been devoted to pinpointing the mental processes that underlie the mere exposure effect. Zajonc made the case that the basic mechanism was classical conditioning.

First observed in Pavlov’s famous experiments with dogs, food, salivation, and bells, classical conditioning describes a process by which an automatic or unconditioned response, which normally follows an unconditioned stimulus, can be turned into a conditioned response, which now follows a previously neutral conditioned stimulus.

The mechanism by which this transfer occurs is repeated co-occurrence in time, the bell is rung just prior to presenting the food, preferably within half a second. Thus are associations built in the minds of both dogs and people.

Zajonc suggested the mere exposure effect works through a similar mechanism.⁴ In this case, the conditioned response is the formation of a positive preference for a repeatedly presented stimulus.

What is the conditioned stimulus? Zajonc argued it was the absence of any negative consequences co-occurring in time with the repeated exposures.

As exposures accumulate, the repeated response stimulus becomes conditioned by this absence of harm associated with each exposure. Over more exposures, this begins to transform the response stimulus into a conditioned response, producing an increase in preference and a greater approach tendency with regard to it.

A primitive association is created in implicit memory: “this thing is familiar and safe, I can approach it with confidence.”

Zajonc’s identification of classical conditioning as the process underlying the mere exposure effect is generally accepted among researchers. Several implications follow. One is that the increased liking effect should not occur if the repeating stimuli are accompanied by negativity or harm.

A phenomenon called distractor devaluation suggests that this is what happens when the potential conditioning stimulus is a distractor that competes for attention with a goal-related task.⁵ In that situation, liking for the distracting stimulus declines rather than increases after the repeated exposures, just as Zajonc’s classical conditioning model would predict.

The mere exposure effect is not universal. In fact, it may not work in one context that is quite common to marketing and advertising, when an ad or marketing message is competing for attention with an unrelated goal-directed task or intention.

Another implication of the classical conditioning model is that mere exposure can have spillover effects. Because “absence of negative consequences” is such a general and diffuse conditioned stimulus, its conditioning effects might be equally diffuse, extending well beyond increasing the attractiveness of the specific object being presented repeatedly.

Zajonc began exploring this possibility in the late 1990s and found that, indeed, repeated mere exposure could have a wider positive effect, influencing both general moods and attitudes toward other objects completely unrelated to the repeated stimulus.

In a series of experiments published in 2000, Zajonc and colleagues found that when people were exposed subliminally to Chinese ideograms at different rates (five exposures each of five ideographs vs. one exposure each of 25 ideographs), those who were shown multiple exposures reported being in better moods than those who were shown only a single exposure.

In addition, Zajonc found increased liking for similar-looking ideograms that were not presented in the conditioning phase of the experiment, as well as for other polygons that were not previously seen and bore no resemblance to the original ideograms.⁶ The overall conclusion from this classic experiment was clear:

The positive emotions induced by repeated mere exposure are diffuse enough to influence both general moods and the ratings of “things” completely unrelated to the repeated objects producing the effect.

Mere Exposure and Intuitive Marketing

Zajonc’s mere exposure effect is an important building block for understanding the science behind intuitive marketing. It demonstrates that positive emotions, such as liking, preferences, and positive moods, do not need “reasons” to be activated, they can be produced by mental processes that do not involve conscious or inferential thinking at all.

If preferences can be generated by noncognitive sources like repetition, it follows that asking people why they prefer one brand or product over another might be problematic. Zajonc recognized this possibility early on:

We buy the cars we “like,” choose the jobs and houses that we find “attractive,” and then justify those choices by various reasons that might appear convincing to others who never fail to ask us, “Why this car?” or “Why this house?” We need not convince ourselves. We know what we like.⁷

Sources of preference that operate below conscious awareness are not deeper “reasons” that lie below traditional articulated “reasons.” They are innate or learned unconscious reactions that precede the very act of reasoning.

The precognitive, preconscious nature of the mere exposure effect can make it hard to accept as an explanation for consumer choices and behavior.

For many, and probably for most of us when we first encounter mere exposure, it just doesn’t feel like a good answer to the puzzle of where preferences come from.

As reasoning creatures who are fully aware of our own conscious reasoning processes, yet blind to the busy unconscious guidance systems that direct so much of our behavior, bypassing the idea of reasons to explain human behavior feels like a cop-out. But it is not.

Ultimately, both marketers and consumers need to overcome this natural resistance to understanding how our minds really work. Until they do, marketers will just continue to make the same old mistakes, polluting our “attentional commons” with annoying and intrusive messages designed to provide us with “reasons” for buying one product or another,

but in the process assaulting our unconscious guidance systems and offending our sensibilities without telling us anything we really want or need to know.⁸