Walking down a residential street in the evening, you might find yourself glancing through the brightly lit windows of the houses you pass. As you peek inside, you take stock of the occupants’ selections: the mahogany chaise lounge with the curved armrests in one house, the sleek leather couches and minimalist paintings in another.

Each person’s aesthetic taste seems distinct, and yet that perception belies a large body of shared preferences. Our team at the University of Vienna, among others, has sought to unravel the patterns and principles behind people’s emotional reactions to objects. Although trends drive certain design decisions, scientists have identified fundamental properties of the mind that consistently dictate which products people tend to like and dislike. Psychologists are now better equipped than ever to explain how you came to choose your belongings in the first place. They can also begin to decipher why you continue to love certain purchases long after they have lost their initial shine, whereas others land in the trash.

Not only are our preferences predictable, they are also flexible. Using ­simple manipulations, researchers can watch you revise your aesthetic judgments in minutes. The essential idea surfaced in the late 1960s, when the late psychologist Robert B. Zajonc, then at the University of Michigan at Ann Arbor, proposed the mere exposure effect: seeing something repeatedly—be it a couch, a car or a coffeepot—boosts its attractiveness. But with repetition comes boredom, recent research suggests, and thus our appreciation for new or different designs. We can largely lose our interest in an object’s appearance, even if we once assumed that looks were everything.

Big and Round
Product designers have long wanted to know what visual features have the power to draw us in or turn us away. Scientists probing the question have identified a handful of guidelines that serve as a starting point. For example, they have found that people prefer large objects to small ones, although no one is quite sure why. Individuals also tend to choose rounded forms over sharper shapes. In a study published in 2006 neuroscientists Moshe Bar and Maital Neta, both then at Harvard Medical School, reported that most consumers prefer curved sofas and watches to those with angular designs. A year later they proposed an explanation. They observed that sharp-edged forms activated neurons in the brain’s fear hub—the amygdala—more strongly than rounded ones did, perhaps because angular objects such as thorns and knives signal danger [see “Building around the Mind,” by Emily Anthes; Scientific American Mind, April/May 2009].

Humans are also attracted to symmetry. Ancient Chinese pottery and 20th-century Western paintings alike exhibit symmetrical shapes and patterns. People are known to prefer symmetrical faces, whose shape may suggest good health and reproductive fitness. In a series of studies psychologist Thomas Jacobsen of the University of Leipzig in Germany and his colleagues found symmetry to be the strongest predictor of beauty judgments among volunteers asked to evaluate basic shapes or abstract patterns.

Other factors, such as an object’s complexity, can amplify visual appeal. We often find complex things prettier than simple ones, with complexity defined as the number of individual elements that make up a picture or shape. In a 2009 study psychologist Pablo P. L. Tinio, now at Queens College, City University of New York, and I documented how both symmetry and complexity figure into people’s judgments of beauty. We asked 16 psychology students at the University of Vienna to evaluate the attractiveness of 160 two-dimensional black-and-white designs grouped into four categories: complex symmetrical, complex nonsymmetrical, simple symmetrical and simple nonsymmetrical. Confirming previous studies of symmetry and complexity, the complex symmetrical patterns were judged the prettiest. Simple symmetrical patterns received the next highest ratings, revealing that symmetry is more important to our impressions of beauty than complexity is. The results also support the idea that combining symmetry and complexity garners higher beauty ratings than does either factor alone.

Comfort Zone
A more subtle factor influencing our aesthetic judgments is our ingrained appreciation for the beauty of the prototype, which is often defined as the statistical average of all examples of that product or item. Because a prototype resembles many different examples of a type, it seems familiar to us even if it is in fact new. Thus, people are attracted to “average” faces—those that result from mathematically combining, say, a few dozen faces, making the proportions of the nose, mouth and eyes, as well as the distances between these features, match the average of the sample. Studies have also shown that we tend to like the aesthetic norm in general, including its appearance in furniture, works of art and even meaningless patterns of dots.

Some researchers have theorized that as with symmetrical faces, prototypes are pleasing because they exhibit no gross irregularities—an extension of our preference for people and animals that appear to be in good health. But cognitive psychologists suggest another explanation, namely, that more typical faces or objects are easier to recognize, providing an efficiency advantage that may stimulate the brain’s reward centers. In a study published in 2001 psychologists Piotr Winkielman, now at the University of California, San Diego, and John T. Cacioppo of the University of Chicago showed 16 volunteers 20 black-and-white drawings of items, such as a horse, dog, bird, house or airplane, they had manipulated to make more or less recognizable. Meanwhile the subjects rated how much they liked the image. To measure the participants’ emotional responses, the researchers recorded the activity of the viewers’ facial muscles with an electromyogram. Winkielman and Cacioppo found that the easier the object was to identify, the better the participants liked it—and the more activity they recorded in the facial muscles used in laughing. The results suggest that ease of recognition is an important factor in likeability.

But the power of prototypes may depend on context because shapes can play with our emotions. In a 2010 study Winkielman and his colleagues investigated whether prototypes might be comforting to people by manipulating the mood of 16 college students. They put some of them in a good mood by asking them to talk about a happy experience and others in a more solemn state by having them recall a sad event. If familiarity offers comfort and feelings of safety, the researchers reasoned, then it ought to be particularly appealing when someone is feeling down. Winkielman’s group showed subjects 14 random dot patterns, all variations of a prototype, followed by a second series of patterns, some of which they had seen and some of which, including the prototype, they had not. In each case, participants rated their liking for the pattern.

The sad people preferred, and smiled at, the images they had previously seen, as well as the prototypes. But the cheerful people reacted differently: they neither preferred the patterns they recognized nor displayed positive emotional responses. They were also not particularly attracted to the prototype patterns. The researchers conclude that familiar forms provide reassurance or security when a person’s mood signals an unsafe environment. Because happy people do not crave such comfort, such tried-and-true designs seem more prosaic than pretty.

Something Old, Something New
But you do not have to be incorrigibly jolly to like a taste of novelty. In 2003 a team led by Paul Hekkert, a professor of form theory at the Delft University of Technology in the Netherlands, reported asking three groups of volunteers, 79 in all, to evaluate various designs of electric sanders, tea­kettles, telephones and cars on their originality and beauty, as well as on how typical they looked. The participants rated the most conventional models as the least attractive, with only slightly warmer reactions to objects with such unusual shapes that their purpose was unclear. The top scores went to designs that coupled originality with classic forms—for instance, prototypes bearing one unusual feature. In other words, the most popular products look innovative while retaining a sense of the known, a principle that American designer Raymond Loewy called “most advanced yet acceptable.”

Product designers may intuitively combine the tried and true with the new. For instance, car manufacturers often try to maintain some continuity of design for the purposes of brand recognition. In some cases, a brand even acquires a recognizable “mood”: designers of the current model Aston Martin DB7 retained the mischievous facial expression of the classic James Bond mobile of the 1960s. But manufacturers also tweak the designs with touches of complexity here and there to stave off buyer boredom—the Aston Martin and the new BMW 7 series, for example, have more lifelike “eyes” for headlights, complete with pupil and iris.

How much novelty a person likes in a particular product—or how easily a person is bored with a design—can depend on how much he or she knows about it. Experts can handle more originality than nonspecialists can. Hekkert and his colleagues have shown that those who know a lot about cars tend to favor unusually original designs. The more innovative a model, the more beautiful the specialists judged it. Similar studies of art connoisseurs suggest that expertise causes people to prefer more abstract or conceptual paintings, sculptures and drawings than amateurs do. Specialists, it seems, are more easily bored.

The expert effect, we reasoned, could result primarily from repeatedly seeing and evaluating a certain class of items. In a study published in 2005 psychologist Claus-Christian Carbon, now at the University of Bamberg in Germany, and I found some support for the idea that sizing up a particular product numerous times increases the liking for more novel, innovative instances of it. We presented 32 people with nine drawings of car interiors representing a range of classic and innovative designs. In each case, we asked a viewer to rate how much he or she liked the interior and how innovative it seemed on a scale of 1 to 7. To simulate repeated exposure, half the subjects looked at each drawing another 25 times, each time judging the degree to which it brought to mind a different adjective—disgusting, say, or pleasant, extravagant, stylish or ornamental. Meanwhile the other participants got a break from the drawings, instead answering unrelated questions about geography. Then we asked everyone again how well he or she liked each design.

In the first round of ratings, we saw that the more classic interiors were the most popular, a finding consistent with our previous work. When we asked ­subjects to judge the pictures a second time, those who had seen each interior just once before stuck with their initial impressions. In contrast, the individuals who had been exposed to the drawings ad nauseam adjusted their preferences toward the more innovative interiors. The classic forms had lost their allure. This ­effect occurs fairly rapidly—after only about 20 minutes of exposure.

For consumers, these findings suggest that a well-informed buyer should spend some time with a product before committing—perhaps by test-driving a new car a couple times or walking around in a new pair of shoes. Even a relatively short experience with an item will likely reflect your long-term preferences better than your initial responses will, and the extra time invested may in fact turn your eye toward more innovative and fun products. For their part, designers may want to concentrate on adding unique features to those major purchases that consumers will own for a long time.

The Smell of Disappointment
Experience affects not just our desire for novelty but also our fondness for complexity. In our 2009 study Tinio and I also found that overexposure to complexity—in this case, viewing detailed black-and-white designs—creates a contrast effect. After repeated exposure to complex patterns, participants judged simple ones to be prettier; equivalently, massive exposure to simple patterns rendered people partial to complexity, making it the overriding factor in their judgment of attractiveness. Symmetry, on the other hand, turns out to be resistant to repetition—participants consistently liked the symmetrical designs.

The influence of long-term experience is not limited to how we see things. Contrary to the main focus of designers—and most scientific studies—looks are not always paramount. In a 2010 study Hekkert and psychologists Anna Fenko and Hendrik N. J. Schifferstein, both at Delft, asked 243 graduate students to report their experiences with a recently purchased product—say, a pair of shoes, a printer or a coffee machine—while buying it and then after the first week, the first month, and the first year of owning and using it. The students reported how much each of their senses contributed to their interactions with the product.

Averaging across 93 different products, the investigators found that an object’s visual impact was strongest at the moment of purchase. After a month of using the product, however, how it felt to the touch became more important than its appearance, and after a year the look, feel and sound of the product were valued equally. “To avoid consumers’ disappointment,” the authors conclude, “retailers should think of ways to demonstrate the nonvisual properties of products at the buying stage (how a computer mouse feels, what kind of noise a coffeemaker makes, and so on).” Of course, the role of the different senses varies with the product—after a year hearing dominated for high-tech products, whereas for shoes their feel and look were equally important.

The large number of influences on our aesthetic judgment might seem to make it difficult to predict our eventual happiness with a purchase. But the research suggests easy guidelines for consumers to follow. We should consider the feel, sound or even smell of something when we are deciding whether to buy it, for example. We should think about our mood at the time: Did it influence our choice of the old-fashioned look over the modern one?

We might also perseverate a little over a potential purchase if it concerns a product we plan to own for a while. And when buying for a friend, bear in mind that your pal may like a more—or less—innovative item than you do if his or her expertise differs greatly from your own. So the next time you find yourself discreetly sizing up the neighbor’s decor—and wondering about the particular objects that populate it—remember that, contrary to the old saying, there is some accounting for taste.