In the fall of 1992, a twentysomething college dropout and former juvenile offender named John Carmack was hard at work in Mesquite, Texas, on a new concept for a video game. It would merge the first-person perspective of a game like Myst with the direct combat of the shooter game Wolfenstein 3-D and the multi-player capacity of Spectre, and it would do so in a more realistic three-dimensional environment than any game before it. The following year, Carmack and his five colleagues at id Software released the product of that vision: Doom.

They knew that they were on to something big. “We noticed that the janitor coming in to empty the trash had just been sitting there staring at the game—for a long time,” Carmack told Time magazine. By August, 1996, Doom had sold two million copies, prompting Wired to name it “the most popular computer game of all time,” and it had spawned a new sub-genre of video game, the so-called “Doom clone.” Though Doom itself was not the original first-person shooter (a game in which, as Nicholson Baker wrote in his 2010 article about video games, “you are a gun who moves—in fact, you are many guns, because with a touch of your Y button you can switch from one gun to another”), it catalyzed the genre’s popularity. First-person shooters are now responsible for billions of dollars in sales a year, and dominate the best-seller lists of current-generation gaming consoles.

What is it that has made this type of game such a success? It’s not simply the first-person perspective, the three-dimensionality, the violence, or the escape. These are features of many video games today. But the first-person shooter combines them in a distinct way: a virtual environment that maximizes a player’s potential to attain a state that the psychologist Mihaly Csikszentmihalyi calls “flow”—a condition of absolute presence and happiness.

“Flow,” writes Csikszentmihalyi, “is the kind of feeling after which one nostalgically says: ‘that was fun,’ or ‘that was enjoyable.’ ” Put another way, it’s when the rest of the world simply falls away. According to Csikszentmihalyi, flow is mostly likely to occur during play, whether it’s a gambling bout, a chess match, or a hike in the mountains. Attaining it requires a good match between someone’s skills and the challenges that she faces, an environment where personal identity becomes subsumed in the game and the player attains a strong feeling of control. Flow eventually becomes self-reinforcing: the feeling itself inspires you to keep returning to the activity that caused it.

As it turns out, first-person shooters create precisely this type of absorbing experience. “Video games are essentially about decision-making,” Lennart Nacke, the director of the Games and Media Entertainment Research Laboratory at the University of Ontario Institute of Technology, told me. “First-person shooters put these tasks on speed. What might be a very simple decision if you have all the time in the world becomes much more attractive and complex when you have to do it split second.” The more realistic the game becomes—technological advances have made the original Doom seem quaint compared with newer war simulators, like the Call of Duty and the Battlefield series—the easier it is to lose your own identity in it.

It isn’t just the first-person experience that helps to create flow; it’s also the shooting. “This deviation from our regular life, the visceral situations we don’t normally have,” Nacke says, “make first-person shooters particularly compelling.” It’s not that we necessarily want to be violent in real life; rather, it’s that we have pent-up emotions and impulses that need to be vented. “If you look at it in terms of our evolution, most of us have office jobs. We’re in front of the computer all day. We don’t have to go out and fight a tiger or a bear to find our dinner. But it’s still hardwired in humans. Our brain craves this kind of interaction, our brain wants to be stimulated. We miss this adrenaline-generating decision-making.”

In February, 2008, Nacke, along with cognitive scientist Craig Lindley, who directs the Intelligent Sensing and Systems Laboratory at Australia’s Commonwealth Scientific and Industrial Research Organization, decided to look at the game-playing experience of the first-person shooter on a physical level: What happens to a player’s body during the game? As gamers played Half-Life 2, one of the most successful first-person shooters, Nacke and Lindley closely observed their physiological responses using electrodes placed on their faces and other parts of the body to monitor muscle movements, pulse, and arousal. The experience was also captured on video, and post-game questions probed the players’ psychological states.

The study was designed to elicit moments of boredom, immersion, and, finally, flow. As the environmental complexity, variety of opponents, and difficulty increased, the players’ faces registered greater positive emotion while their skin indicated increased arousal. Subjectively, they reported feeling happier and more immersed in the experience. They also felt an increase of challenge and tension—Csikszentmihalyi’s optimal match between skill and challenge—as well as a heightened sense of action as their own identity melted away. Before zeroing in on first-person shooters, Nacke had looked at a number of other games, such as the third-person shooter Kane & Lynch and the real-time strategy game Fragile Alliance, comparing the experience of play in the different environments. “In the more casual games,” Nacke said, “it’s more about problem-solving. We didn’t see the same absorption, the same engagement flow that we have in first-person shooters.”

Nacke and Lindley aren’t the first people to find a connection between flow and first-person shooters. In a 2005 study that looked at the experience of playing thirteen popular games, Half-Life 2 yielded the greatest degree of total player immersion—that is, the extent to which the player is completely engaged in the game on a sensory, challenge-based, and imaginative level. The attraction, the researchers found, didn’t come from plot and narrative—it came from that same sense of control and decision-making that Csikszentmihalyi and Nacke identify as crucial for engagement to occur. Or, to put it in the words of a twelve-year-old player, “The main part is moving things yourself and such … the plot is just secondary.”

Control, compounded by a first-person perspective, may be the key to the first-person shooter’s enduring appeal. A fundamental component of our happiness is a sense of control over our lives. It is, in fact, “a biological imperative for survival,” according to a recent review of animal, clinical, and neuroimaging evidence. The more in control we think we are, the better we feel; the more that control is taken away, the emotionally worse off we become. In extreme cases, a loss of control can lead to a condition known as learned helplessness, in which a person becomes helpless to influence his own environment. And our sense of agency, it turns out, is often related quite closely to our motor actions: Do our movements cause a desired change in the environment? If they do, we feel quite satisfied with ourselves and with our personal effectiveness. First-person shooters put our ability to control the environment, and our perception of our effectiveness, at the forefront of play.