The Mere Exposure Effect (The Familiarity Principle) in a Nutshell: Normally, familiarity breeds liking, at least to a certain point. So the more people are familiar with you or your idea, the more they will like it and be influenced by it. Yet, familiarity is not always helpful. First, increased exposure may have no effect or even negative effects when initial impressions are sour. Second, more familiarity leads to less liking if it reveals differences and unlikeness.
Avoidance of Novel Stimuli
All organisms, including humans, react with fear and avoidance to any novel stimulus, including objects, sounds, or other living beings. A new stimulus may harbor a threat so it makes sense to be cautious. If during the first encounter, nothing bad happens, then during the repeated exposures organisms move from fear and avoidance to approach. Slowly, with each exposure, our liking of that stimulus increases.
For example, when first exposed to a strange sound, the human baby reacts with fear and crying. When the baby hears the same sound for the second time, he will show displeasure but won’t cry. On the third exposure, the baby might not show any displeasure. And on the fourth exposure, the baby may show an obvious interest. Of course, such reaction is not the trademark of human babies but applies to all organisms. Research shows, for example, that it works even in embryonic state: in one study, two sets of fertile sets of chicken eggs were exposed to tones of two different frequencies; when the chickens hatched, they preferred the tone to which they were exposed prenatally.
Zajonc’s Mere Exposure Effect
In 1960s, Robert Zajonc noticed that novel stimuli appear threatening, but with each repeated exposure people come to like a particular stimulus more and more. In his groundbreaking paper published in 1968, Zajonc established the mere exposure effect, suggesting we come to like a particular stimulus more and more with each repeated exposure to it. To show the mere exposure effect, Zajonc asked his subjects to rate the “goodness” of various meaningless stimuli. For example, Zajonc showed his subjects various Chinese-like characters (shown below) and the subjects, thinking the characters represented adjectives, had to rate whether they meant something positive or negative. All these characters, however, were meaningless. And of course, Zajonc showed some characters more often than the others. As Zajonc predicted, the more frequently his subjects saw a character, the more likely they thought the character meant something good.
Zajonc tested the mere exposure effect with other stimuli, including nonsense words (e.g. Iktitaf, Biwojni, Civadra, Kadirga, Enanwal) and photographs of unknown men. The more frequently people encountered a particular stimulus, the more they liked it. In fact, Zajonc began his paper by mentioning an Associated Press article about a college student who wore a big black bag:
A mysterious student has been attending a class at Oregon State University for the past two months enveloped in a big black bag. Only his bare feet show. Each Monday, Wednesday, and Friday at 11:00 A.M. the Black Bag sits on a small table near the back of the classroom. The class is Speech 113— basic persuasion. . . . Charles Goetzinger, professor of the class, knows the identity of the person inside. None of the 20 students in the class do. Goetzinger said the students’ attitude changed from hostility toward the Black Bag to curiosity and finally to friendship.
Familiarity with People
The mere exposure effect suggests that the more we are familiar with a certain person, the more we will like him or her. And this explains why we may trust celebrities more than they deserve, or why, for example, some politicians stand a better chance of being elected. And research generally supports this idea that repeated exposure to a person, just like to any other stimulus, leads to increased liking.
The Mere Exposure Effect and Investments
The mere exposure effect is pervasive, and it explains many tendencies in the business world. For instance, in the financial sector, familiarity leads people to invest in the companies from their region, especially in the companies they work for. This also explains the home country bias in investment, as stock traders are more familiar with domestic companies and they invest there even when other markets offer better alternatives.
Negative Effects of Familiarity
Familiarity is not always helpful. First, increased exposure may have no effect or even negative effects when initial impressions are negative. So positive first impressions are crucial. Second, too much exposure can lead to habituation and less liking over time. Ideal number of exposures differs with different stimuli. For example, you might like less a particular painting if you have been exposed to it 20 times over a few days; however, hearing the same new song 20 times over 3 days might not lead to less liking.
When Familiarity Breeds Contempt: Familiarity and Impressions of Dissimilarity
Finally, when it comes to familiarity with people, more familiarity leads to less liking if it reveals differences and unlikeness. A 2007 study by Michael Norton, Jeana Frost, and Dan Ariely suggests that familiarity is harmful when it leads to more personal information and this information shows differences. Such differences will create impressions of dissimilarity and this will lead to less liking. The researchers nicely summarized their study:
Benjamin Franklin proposed that fish and visitors have something in common: Both begin to stink after 3 days. The present research offers empirical support for Franklin’s quip. The more people learn about others—and anyone who has had houseguests knows all too well how much one can come to know in a short time—the less they like them, on average . . . many prospects, whether world leaders or would-be hipsters, who looked good from afar suddenly seem less attractive once more is known.
In this context, Roman philosopher and orator Lucius Apuleius was right: familiarity breeds contempt, but privacy gains admiration. However, familiarity is valuable as long as it does not lead to dissimilarity. (This is what usually happens between romantic partners: more familiarity leads to more liking, not less; of course, the reason why people usually become romantic partners is that in the first place they share more similarities between themselves than they do with other people.)
So if you can predict that more familiarity will lead to impressions of dissimilarity, then it is better to hold down any attempts to get more familiar and apply the mere exposure effect only to similarities.
 D.W. Rajecki, Effects of Prenatal Exposure to Auditory or Visual Stimulation on Postnatal Distress Vocalizations in Chicks, Behavioral Biology, 11, 525–536 (1974).
 Robert B. Zajonc, Attitudinal Effects Of Mere Exposure, Journal of Personality and Social Psychology (Monograph Supplement), 9 (No. 2, Pt.2), 1–27 (1968).
 Richard L. Moreland and Scott R. Beach, Exposure Effects in the Classroom: The Development of Affinity Among Students, Journal of Experimental Social Psychology, 28, 255–276 (1992).
 Gur Huberman, Familiarity Breeds Investment, Review of Financial Studies, 14, 659–680 (2001).
 Walter C. Swap, Interpersonal Attraction and Repeated Exposure to Rewarders and Punishers, Personality & Social Psychology Bulletin, 3, 248-251 (1977).
 Michael I. Norton, Jeana H. Frost, Dan Ariely. Less Is More: The Lure of Ambiguity, or Why Familiarity Breeds Contempt, Journal of Personality and Social Psychology, 92, 97–105 (2007).