The mere-exposure effect is a psychological idea that explains how people often start to like or dislike things simply because they are familiar with them. In social psychology, this idea is sometimes called the familiarity principle. Studies have shown this effect works with many different things, such as words, Chinese characters, paintings, pictures of faces, geometric shapes, and sounds. In research about how people feel about each other, it has been found that the more often people see another person, the more they tend to find that person pleasant and likeable.

Research

Gustav Fechner performed the earliest research on this effect in 1876. Edward B. Titchener also studied the effect and described the "glow of warmth" people feel when they see something familiar. However, his idea was rejected because experiments showed that people’s preference for objects did not depend on how familiar they thought the objects were. This rejection led to more research and the development of current theories.

The scholar most known for creating the mere-exposure effect is Robert Zajonc. Before his research, Zajonc noticed that when organisms first see something new, they often feel fear or avoid it. Each time they see the same thing again, they feel less fear and more interest. After seeing it many times, they begin to like it. This observation led to the study of the mere-exposure effect.

In the 1960s, Zajonc’s experiments showed that people rate familiar things more positively than unfamiliar ones. At first, he studied how often words were used and found that positive words appeared more often than negative ones. Later, he found similar results with other stimuli, such as shapes, drawings, photos, made-up words, and symbols.

In 1980, Zajonc proposed the affective primacy hypothesis, which suggests that feelings, like liking something, can happen with very little information. Through experiments, he tested this idea by showing people repeated images so quickly that they did not recognize them. Even without conscious awareness, people still liked the images more. Zajonc compared results from images shown for longer periods (when people recognized them) to those shown briefly (when they did not). He found that people who did not recognize the images liked them more quickly.

One experiment used chicken eggs. Before hatching, chicks heard different tones. After hatching, they were played both tones and consistently chose the one they had heard while still in the egg.

Another experiment showed people Chinese characters for short times. Later, they were asked if the symbols seemed positive or negative. Symbols they had seen before were rated more positively than those they had not. In another test, people who saw the symbols were asked about their mood. Those who saw the symbols more often reported feeling better.

In another variation, people saw images on a screen for a very short time, too fast to notice. Even without conscious awareness, they still liked the images more. However, these subliminal effects usually only happen in controlled experiments.

Zajonc argued that the mere-exposure effect can happen without conscious thinking, and "preferences need no inferences." This idea led to more research on how thinking and feelings are connected. He explained that if people liked things only because of information attached to them, persuasion would be easier. But he said this is not true because simple persuasion methods often fail. Zajonc noted that feelings happen faster than thinking and are often more confident. He stated that thinking and feeling are separate but connected: "feeling accompanies all thinking, arises early in the process of remembering, and comes from a separate system in the body."

Zajonc claimed there is no proof that thinking happens before decisions. While many people assume this, he argued that decisions often happen without much thinking. He said that people decide first and then find reasons to explain their choices.

Charles Goetzinger tested the mere-exposure effect in his class at Oregon State University. He had a student appear in a large black bag with only his feet visible. The bag sat in the back of the classroom. Over time, students first reacted with hostility, then curiosity, and finally friendship. This confirmed Zajonc’s theory that repeated exposure to a stimulus can change attitudes. As Zajonc said, "mere repeated exposure of the individual to a stimulus is a sufficient condition for the enhancement of his attitude toward it."

A review of 208 experiments found that the mere-exposure effect is strong and reliable, with an effect size of r = 0.26. This effect is strongest when unfamiliar things are shown briefly. It usually works best after 10–20 exposures, but liking may decrease after too many exposures. For example, people often like a song more after hearing it a few times, but too many repeats can reduce this liking. Delaying the time between exposure and measuring liking often makes the effect stronger. The effect is weaker in children and for drawings and paintings compared to other stimuli. One study showed that repeated exposure to people we dislike can make us dislike them even more.

Zola–Morgan’s experiments with monkeys showed that damage to the amygdala (a brain area linked to emotions) harms emotional responses but not thinking. Damage to the hippocampus (a brain area linked to memory) harms thinking but not emotions.

Research shows that liking for a stimulus increases with more exposure but eventually decreases, forming an inverted-U shape. This pattern has been observed for at least thirty years.

Perceptual fluency

The mere-exposure effect suggests that seeing something many times makes it easier to process. This ease of processing, called perceptual fluency, leads to more positive feelings. Studies show that repeated exposure increases perceptual fluency, which supports the idea that it helps with positive feelings in personal memories and learning through experience. Later studies confirmed these findings.

Application

The most obvious use of the mere-exposure effect is in advertising. However, research about how well this effect improves people’s opinions of companies and products has shown mixed results. One study tested the effect using banner ads on a computer screen. College-age students read an article on the computer while banner ads appeared at the top of the screen. The results showed that students who saw the "test" banner ad liked it more than those who saw other ads less often or not at all. This study supports the idea of the mere-exposure effect.

Another study found that higher levels of media exposure are linked to lower reputations for companies, even if the exposure is mostly positive. A later review of the research suggested that exposure can create mixed feelings because it leads to many different thoughts, some good and some bad. Exposure is most helpful when a company or product is new and unknown to people. There may not be a perfect amount of exposure that works best for an advertisement. In a third study, researchers gave some consumers happy or unpleasant images before offering them a drink. Those who saw the happy image bought more drinks and were willing to pay more than those who saw the unpleasant image. This study supports the idea that people often choose things they like, even without thinking deeply about them.

In advertising, the mere-exposure effect suggests that people do not need to think about ads. Simple repetition can create a memory in the mind and influence behavior without conscious effort. One scholar explained this idea by saying that the tendency to approach something after seeing it many times may happen before people form opinions about it.

The mere-exposure effect appears in many areas of decision-making. For example, many stock traders invest in companies they are familiar with, even if other companies offer better choices. The effect also influences how people rate academic journals. Academics who have worked with a journal before rate it much higher than those who have not. Research on whether exposure can improve relationships between groups has shown mixed results. When groups already dislike each other, more exposure can increase hostility. A study of voting patterns found that how much people see a candidate affects how many votes they receive, separate from how much people like the candidate’s policies.