For a period of several weeks, readers of Michigan student newspapers noticed a small ad-like box that appeared on the front page, containing nothing but a single foreign word. The words were Turkish or Turkish-sounding; some appeared several times and some only once. Anyone who asked the editors what was going on were told only that the advertiser wished to remain anonymous.
Psychologist Robert Zajonc was studying what he called the “mere exposure effect.” After the ads had run for several weeks, with some appearing more often in the University of Michigan newspaper and others being shown more frequently in the Michigan state publication, Zajonc’s research team sent questionnaires to students asking their impression of whether the words meant something good or something bad. The overwhelming result was that the words that had been seen more often were more likely to be rated as “good.” The results have been replicated many times, and the effect has been demonstrated even when words are shown so quickly that the conscious mind cannot register them.
The effect has also been shown in animals. Chicken eggs were exposed to different tones; when the chicks hatched, they showed less distress when exposed to the same tones they had been exposed to in the egg. Zajonc theorizes that the effect is biologically useful because an unfamiliar stimulus may indicate danger. Animals who are not suspicious of new situations may not survive long, but exposure to the same sights and sounds without anything bad happening causes the stimulus to be perceived as a sign of safety.
This and similar experiments are described in Daniel Kahneman’s book, Thinking, Fast and Slow.