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The app "Candy Crush" has over 93 million users playing over 1 billion times per day. If you missed the bandwagon, you can get up to speed in seconds. All you do is touch a candy and swipe it with your finger.



RATH: Match three identical candies to crush them and get to the next level.



RATH: But before you start swiping, I need to warn you - it is very habit-forming. Natasha Dow Schull is an associate professor at MIT. She says the thing that keeps users play so much as what she calls the ludic loop.

NATASHA DOW SCHULL: Ludic would be pure process. It's you and the machine. There is no real character development or narrative arc. Kill the monster, kill monster again, kill the monster again. You never know when you're going to get the reward, how much the reward will be. It's these little ludic loops.

RATH: Schull spent more than a decade making trips to Las Vegas casinos all in the name of science. She says that ludic games, like "Candy Crush," rely on the same psychological hooks as slot machines.

SCHULL: I think I've heard the expression, "Candy Crush" is like a slot machine on steroids. They're quite similar. Its solitary, so it's just you and you're interacting with the screen. You're not waiting for other people. It's just pure repetition, pure procedure. And then there's the element of speed. You are just playing in rapid succession. I know with slot machines, you can play 1,200 hands an hour. I'm not sure how many games of "Candy Crush" you can play. But my understanding is that it's even more of a just continuous process where you don't even really distinguish between one spin or game and the next. You're just going, going, going. And that, that really is the last characteristic. The continuity - continuous, steady stream of small, little reinforcements.

RATH: Speaking of reinforcements and rewards, you know, when you're talking about slot machines, it's sort of easy to understand that reinforcement 'cause, at least occasionally, you'll get a payout. You'll get money back. With these video games, though, you don't get anything like that.

SCHULL: Actually, with these newer digital games, it's really not about winning. One gambler told me - and this really drove the point home - I get irritated when I win a jackpot. And I kept hearing that over and over again. And that sort of flipped the whole thing on its head for me. And they said, you know, I'm there to just keep going. And when I win a jackpot, I have to - everything freezes up. People look over at me. Suddenly I'm back in the world, and sometimes I have to wait for the change person to come and pay me off. To me, that just speaks worlds about this trend toward playing for something else. And, you know, what is that something else? What is that something else that's shared with "Candy Crush" and slot machines? I think it's a kind of escape - the retreat from the world, the comfort. So people actually describe these machines of chance as being reassuring and predictable, which is really counterintuitive, but it makes sense if you sit and watch people play. They're modulating their moods just as people are with "Candy Crush."

RATH: Is that the machine zone?

SCHULL: The gamblers actually call it the machine zone. And I took that term from them because I think that term really nicely captures what's going on. And I think that it can be applied more broadly than just slot machines. It can be applied to compulsive e-mail checking or Ebay auctions or playlists where you're constantly using this media to modulate your mood. And you just have it available right there at your fingertips.

RATH: Natasha Dow Schull is a cultural anthropologist and an associate professor at MIT. She's also the author of "Addiction By Design: Machine Gambling In Las Vegas." Natasha, thank you.

SCHULL: Thank you.

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