Psychologists studying personality have long looked at the extreme traits of extroverts and introverts. Now they are focusing on the ambiverts in the middle. PHOTO: DAVE WHAMOND

By

ELIZABETH BERNSTEIN

Emeroy Bernardo enjoys spending time alone, meditating, exercising and working. When he goes out for dinner or drinks with friends, he sometimes quietly observes people’s facial expressions and body language. Often when he’s shopping or running errands, he ignores people he knows—pretending he doesn’t see them—to avoid small talk.

Still, the 27-year-old dance instructor who lives in Glendale Calif., considers himself friendly and meets new people almost everywhere—at the gym, at Starbucks, waiting to board a plane. At parties, Mr. Bernando is often the guy who starts a dance circle and then shows off his break-dancing moves.

Is Mr. Bernardo an introvert or an extrovert?

He is an ambivert, a solid mix of both.

The personality traits of extroversion and introversion fall on a spectrum, and most of experts’ focus has been on the two ends. Now, social psychologists, behavioral scientists and business experts are taking a closer look at the overlooked category smack in the middle—ambiversion—and deciding that people with this trait may have some personal and professional advantages for being adaptable.

Experts believe that the personality traits on the introvert-extrovert spectrum remain stable throughout life—they appear as early as infanthood and are difficult to change. On one end are extroverts (sometimes spelled “extravert” in psychology circles) who become energized externally. They love to have lots of people around them and to be the center of attention. They enjoy brainstorming with others and often form their thoughts as they speak. When by themselves, they easily become bored or restless.

Introverts, on the other end of the spectrum, become energized internally. They prefer to spend time alone, with one other person or with a small group. They feel drained by a lot of social interaction or a crowd. They gather their thoughts carefully before they speak.

Ambiverts have introverted and extroverted traits, but neither trait is dominant. As a result, they have more balanced, or nuanced, personalities. They aren’t the folks yammering your ear off. Nor are they the totally silent ones happily ensconced in the corner.

Ambiverts move between being social or being solitary, speaking up or listening carefully with greater ease than either extroverts or introverts. “It is like they’re bilingual,” saysDaniel Pink, a business book author and host of Crowd Control, a TV series on human behavior, who has studied ambiversion. “They have a wider range of skills and can connect with a wider range of people in the same way someone who speaks English and Spanish can.”

You can tell if you’re an ambivert by asking yourself how you’d behave in common situations. What do you crave after a long day at work when you need to refuel—a happy hour with friends, or your couch and the remote control? At a social event, at what point do you want to leave—as soon as you get there or after the last person has left? In a conversation, do you prefer to think through your answers before speaking, or throw out whatever idea comes to mind and bat it back and forth? (Mr. Pink, the author of “To Sell Is Human: The Surprising Truth About Moving Others,” has developed a quiz.) If you’re an ambivert, your preference will often be somewhere in the middle—you choose to have a drink with a friend after work but then afterward go home and take a long walk with the dog.

A study of ambiverts, published in June 2013 in the journal Psychological Science, looked at 340 outbound call-center representatives. It showed that the social and emotional flexibility of the ambiverts in the group made them superior sales people. The participants filled out a 20-measure personality test, then the researcher assessed each person’s sales revenue for the next three months, controlling for other variables. The employees with the highest revenue per hour—an average of $208, compared with $138 for the full sample—were ambiverts who had a personality test score exactly between extroversion and introversion.

“Ambiverts are like Goldilocks—they offer neither too much nor too little,” says Adam Grant, an organizational psychologist and professor of psychology at the University of Pennsylvania’s Wharton School. He believes this emotional acuity gives ambiverts unique skills in parenting and marriage as well.

The drawback to being an ambivert, Dr. Grant says, is that it can sometimes be difficult for them to know which side of their personality to lead with in a given situation. Unlike extroverts and introverts, who tend to know what energizes them, ambiverts may not always be so sure. That means they can sometimes get stuck—not realizing that they need to change their approach to feel more motivated.

Carl Jung popularized the concepts of extroversion and introversion in the early 1920s; he identified a third group but didn’t name it or write much about it. It wasn’t till the 1940s that the term “ambivert” began to be commonly used by psychologists.

Ambiversion has gotten more attention in recent years, as books, TEDx talks and consulting firms have sprung up focusing on introversion and how personality traits impact people’s behaviors in marriages, families and work. More than half the population is ambiverted, according to Wharton’s Dr. Grant. His research shows that roughly two-thirds of people are ambiverts, while one-third are either strong introverts or strong extroverts.

“An introvert and an extrovert know pretty quickly what they crave,” says Laurie Helgoe,author of “Introvert Power: Why Your Inner Life is Your Hidden Strength” and assistant professor in the department of psychology and human services at Davis & Elkins College in Elkins, W.Va. She says introverts generally want to pull away from stimulation or interaction and regroup, while extroverts want to seek out people and activity. Ambiverts could go either way, based on the situation, she says.

If you’re an ambivert, be mindful of it, says Dr. Helgoe. “If you are aware that you can go both ways, then you can look at a situation and see what behaviors are going to be most effective and rewarding.”

Think of “introvert” and “extrovert” as verbs, says Beth Buelow, a speaker and coach who is founder of The Introvert Entrepreneur, a website for introverts. “You can choose to introvert (turn inward) or extrovert (project outward) depending on what’s called for.”

Wharton’s Dr. Grant cautions that ambiverts should try not to get stuck in either an introvert or extrovert role. Ambiverts should remain nimble. Also, sticking with one or the other tendency too long might leave an ambivert drained. The warning signs will be boredom or burnout.

Dr. Grant recommends “unleashing your inner ambivert.” “Read each situation more carefully,” he says, “and ask yourself, ‘What do I need to do right now to be most happy or successful?’”

Write to Elizabeth Bernstein at elizabeth.bernstein@wsj.com or follow her on Twitter and Facebook at EBernsteinWSJ.