How Slot Machines Trick Your Brain

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Here’s how scientists made a slot machine for rats: They added three flashing lights and a pair of levers to a sugar pellet dispenser. With all three lights illuminated, the rats “won” and could press one lever for a pellet. If zero, one, or two lights were lit, the rats hit a different lever to play again.

The rodent gamblers were good at differentiating a win from a loss—with one exception. With two lights illuminated, a near miss, they often pressed the lever for the sugar cube. This is consistent with previous research on gambling. People keep playing because losing feels like winning.

Paul Cocker, a researcher at the University of British Columbia, recently published a study based on his team’s work in Biological Psychiatry. It’s notable for two reasons: First, it involved building a slot machine for rats! Second, it could be a step—albeit an early one— toward development of a drug to treat compulsive gambling.

Once the rats had been trained on the machine, Cocker gave them drugs that blocked dopamine D4 receptors, a part of the brain associated with pleasure. While untreated rats had thought that two lights signified a win, they now figured out they’d lost. Cocker says he’s not a “human person”—he only studies rats. But the next step would be for researchers to see if people who are given similar drugs would lose the urge to keep playing once they realized they were losing all the time.

Any treatment is “somewhere far off in the future,” Cocker says, but when researchers are ready to fiddle with humans’ neurological processes, they’ll be dealing with worthy opponents in the gambling industry. Digital slot machines have been designed to carefully cultivate people’s cognitive weaknesses to keep them from becoming frustrated and leaving.

One way to do this is to obscure the low chances of winning. While a video slot machine seems to mimic the analog version, the virtual fruits aren’t spinning. They’re simply decorations to occupy the player’s mind as a random number generator determines whether the player won. And the visible symbols imply a much better chance of winning, according to Addictive By Design, a book on machine gambling by Natalie Dow Schüll, an assistant professor at the Massachusetts Institute of Technology. A reel on a virtual slot machine may seem to be cycling between 22 positions, but the machine powering it could have 64. This means you’re seeing those cherries moving by way more than the odds that they will stop. Schull cites a study by Kevin Harrigan, an expert in algorithms, which says that if this type of machine were to pay off according to what people are seeing, players would win 297 percent of the time.

But machines aren’t designed only to make it seem as if you might win the next time. Increasingly, even losers are winners. Many digital slot machines are based on a grid of symbols, where players can bet that a winning combination will come up on any number of vertical, horizontal, or diagonal lines. Instead of placing a single bet for, say, $5, those machines spread that money over 50 bets, each for a dime. Chances are, some of those dimes are going to be winners, and the machine will give you positive reinforcement even if 49 of those bets didn’t go your way. “So it’s a net loss, but you get the audio-visual stimulation saying you won,” says Schüll. “Your body always experiences it as a win.”

It isn’t surprising that rats, like humans, could be tricked into believing they’d won games they’d lost. Treating such a tendency with a drug, however, could be a fraught exercise. “It may be that all people, like all rats, have this tendency to interpret losses as wins in certain circumstances,” says Schüll. “Then what do you do with that?”