Introversion, thanks largely to Susan Cain's 2012 best seller Quiet, is having something of a cultural moment. Once a mostly misunderstood personality trait — and often considered a behavioral defect when it was considered at all — it's now the subject of countless other books and online listicles (and, more recently, parodies of listicles). And as more regular, non-scientist types started to talk about introversion, psychologist Jonathan Cheek began to notice something: The way many introverts defined the trait was different from the way he and most of his academic colleagues did. 

"When you survey a person on the street, asking them to define introversion, what comes up as the prototypical characteristics ... are things like thoughtful or introspective," said Cheek, a psychology professor at Wellesley College. And yet neither of these things are part of the definition of the trait according to scientific literature. In the bulk of the research on personality psychology, introversion is usually defined by what it is not: extroversion. If extroverts are assertive and enthusiastic individuals who thrive in highly stimulative social environments, then introverts are the opposite. End of list. What introverts think about it doesn't really factor in. 

This is actually a problem that was identified at least as early as 1980, when one study found that the "scientific" and "common-sense" definitions of introversion didn't quite match up. And the more Cheek and his colleagues, including graduate students Jennifer Grimes and Courtney Brown, thought about it, and the more self-described introverts they interviewed, the less correct this one-size-fits-all definition seemed. There's not just one way to be an introvert, Cheek now argues — rather, there are four shades of introversion: social, thinking, anxious, and restrained. And many introverts are a mix of all four types, rather than demonstrating one type over the others. (Scroll to the bottom for a quiz to find out your own type.)

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Taken together, the first letter of the four types spells out STAR, which is what Cheek named his model. He designed it by surveying about 500 adults, ranging in age from 18 to 70, asking them about things like their preference for solitude, or how inclined they are to daydream. The uniting principle of all four kinds is, of course, a tendency to turn inward rather than outward — but beyond that, it gets more complicated. 

Here's a brief description of each: 

Social: Social introversion is the closest to the commonly held understanding of introversion, in that it's a preference for socializing with small groups instead of large ones. Or sometimes, it's a preference for no group at all — solitude is often preferable for those who score high in social introversion. "They prefer to stay home with a book or a computer, or to stick to small gatherings with close friends, as opposed to attending large parties with many strangers," Cheek said. But it's different from shyness, in that there's no anxiety driving the preference for solitude or small groups. 

Thinking; Thinking introversion is a newer concept. People with high levels of thinking introversion don't share the aversion to social events people usually associate with introversion. Instead, they're introspective, thoughtful, and self-reflective. "You're capable of getting lost in an internal fantasy world," Cheek said. "But it's not in a neurotic way, it's in an imaginative and creative way." Think the dreamily imaginative Luna Lovegood, not the socially awkward Neville Longbottom, Cheek said, putting it into Harry Potter terms I, for one, am deeply familiar with. 

Anxious: Unlike social introverts, anxious introverts may seek out solitude because they feel awkward and painfully self-conscious around other people, because they're not very confident in their own social skills. But, often, their anxiety doesn't fade when they're all alone. This kind of introversion is defined by a tendency to ruminate, to turn over and over in their minds the things that might or could or already have gone terribly wrong. 

Restrained: Another word for this one is reserved. Restrained introverts sometimes seem to operate at a slightly slower pace, preferring to think before they speak or act. They also might take a while to get going — they can't, for instance, wake up and immediately spring into action. Haruki Murakami's What I Talk About When I Talk About Running contains a passage that I think neatly illustrates the restrained introverts, when he discusses how it takes his muscles a while to warm up when he starts to run. "When I put on my jogging shoes in the morning and set out, my feet are so heavy it feels like I'll never get them moving," he writes. He says it's the way his mind works, too: slow to get going. Murakami, I would bet, is a restrained introvert. 

So far, Cheek's model of the "four meanings of introversion" is just a working paper. But many psychologists I spoke to, such as Scott Barry Kaufman, scientific director of the Imagination Institute at UPenn's Positive Psychology Center, think it's an important step forward in expanding the meaning of introversion. "I do think it's best to talk about different types of introversion rather than lump all of its aspects together under a single umbrella," he said. Kaufman has written about Cheek's model for Scientific American, and also used it as part of a basis for a new test measuring introversion for the Quiet Revolution, a kind of for-introverts/by-introverts website launched earlier this month by Quiet author Susan Cain. "Even people who do understand introversion still imagine that it's really just about, Would you rather be on your own or with a close friend?" Cain told me. "In fact, there's so much more than that."

Instead of working to correct the public's perception of the word, Cheek is essentially seeking to transform the way personality scientists think of the trait, by expanding the definition. "Many people do not feel identified or understood just by the label introversion as it's used in the culture or by psychologists. It doesn't do the job — it helps a little bit, but it just doesn't get you very far," Cheek said. "It turns out to be more of a beginning."

If you're curious where you rank in this newer theory of introversion, take Science of Us's quiz below, which is designed based on Cheek's model.

http://nymag.com/scienceofus/2015/06/apparently-there-are-four-kinds-of-introversion.html?mid=cnnhealth