Dig through enough recent psychology research and you might walk away thinking that some scientists seem to have a gambling addiction. You would be half right: researchers turn to gambling again and again, but they are not in it to rack up money. Psychologists are interested in gambling as a powerful tool for investigating risk-taking, decision-making, and how the brain responds to personal gains and losses.

Two recent gambling studies offer insights not only into general human behavior, but into the psychology of gambling itself—that is, how our minds work when we hit the casino or pull out our favorite deck of cards for an evening's entertainment with friends. The studies suggest that the best "poker face" is not a neutral expression, but a trustworthy one, and that even when we are merely spectators, our brains respond as though we have something tangible to win or lose.

In a study published online July 21 in PLoS ONE, Wellesley College psychologist Erik Schlicht and his colleagues examined how our opponents' faces influence the way we bet in poker.

Schlicht recruited 14 adult participants for the study, most of whom were novices that played fewer than 10 hours of poker a year. The experimenters asked the participants to sit down at computers and individually run though hundreds of scenarios in a simulated and highly simplified version of Texas hold 'em. On the computer screen, participants saw their two-card starting hand, any one of 100 digitally animated faces to represent a computer opponent, and two poker chips representing each player's bets. In the study's tweaked version of poker, the participants always bet 100 chips and the computer always bet 5,000 chips. The researchers also told participants that opponents might have different styles of playing poker, but did not explain anything about the animated faces. Based solely on this information, participants had to decide whether to fold (give up) or call (play their hand against that of the opponents). A decision to fold would assure that the participant lost 100 chips, but calling offered the chance to win or lose 5,000 chips, depending on whether or not he had the winning hand.

During each simulated game, subjects saw a random set of 300 variations of 100 simulated faces, whose expressions were modified along a spectrum of trustworthiness: Some appeared trustworthy, others untrustworthy and still others neutral. To make sure they isolated the influence of the opponents' faces on wagering behavior, the researchers kept the values of the participants' hands equal while varying the conditions of trustworthiness. If the participants relied on facial expressions when deciding how to bet, the researchers argue, then their decisions should systematically vary between conditions. If participants relied solely only on the strength of their hands to make their choices, then their rates of folding or calling would not differ significantly between conditions.

One kind of facial expression made a big difference, but it was not the disinterested countenance we normally associate with the phrase "poker face." Instead, trustworthy faces were the game-changer. Not only did participants take much longer to make a decision—which suggests greater deliberation—when looking at trustworthy expressions, they also made more mistakes and folded more frequently. In other words, trustworthy faces threw off their games.

"Different people made the same inferences about opponents' playing styles based on facial information alone," Schlicht says. "People become more conservative in wagering when faced with trustworthiness, which leads to more folding." Whether this is because people have an instinctive emotional reaction to trustworthy faces or employ a conscious strategy remains unclear. "It could just be an emotional reaction or the other interpretation is that it's kind of a rational thing to do: If a person looks trustworthy it's probably because they are only betting with good hands," says Schlicht.

Although the study finds that neutral expressions were not the most effective poker faces, the researchers point out that their findings rely on a very simplified version of poker and only apply to novices. "This doesn't necessarily work against experts," Schlicht says, "but this might suggest that when you have little information about your opponents and people aren't going to know what style of bettor you are, you might be able to take advantage of the situation by appearing more trustworthy. Smile a lot, look emotionally pleasant." To learn more about the study and its implications, visit this FAQ written by Schlicht.

Another recent gambling study, published online July 29 in BMC Neuroscience, suggests that when we watch others gamble, our brains respond as though we are gambling, too. Josep Marco-Pallarés, a psychologist at the University of Barcelona in Spain, set up pairs of participants in front of computers to play a very simple gambling game based on chance. The computer screens repeatedly displayed two numbers: 25 and 5. The gambling participant picked one of the two numbers at random by pressing a button. Once he made his choice, one of the numbers lit up green and the other turned red. If the gambler chose the "correct" green number, he would earn a corresponding number of euro cents—so correctly guessing 5 would gain the gambler 5 euro cents. On the other hand, guessing incorrectly would lose the gambler the same amount of euro cents as whichever number turned red. The other participant simply served as a spectator trial after trial. The gambler's success or failure determined how much bonus money one or both earned (on top of what they were already paid as study subjects).

The experimenters placed electrode nets on the scalps of both gamblers and spectators, using electroencephalography (EEG) to measure event-related potentials (ERPs)—characteristic brain responses to applied stimuli, whether a visual task, loud noise or successful bet. In the study, voltage changes in electrical activity of the brain during gambling were averaged across many trials to obtain characteristic ERP signatures for winning and losing. The researchers expected the active gamblers to have distinct brain responses to successful and unsuccessful wagers—which they did—but they also wanted to test how the spectators' neural activity changed depending on their attitudes toward the gamblers.

In one situation observers lost or gained Euro cents along with the gambler. In another a win for the gambler meant a loss for the spectator and vice versa. In the third observers were completely neutral as to whether or not gamblers won or lost because they knew they would receive the maximum amount of bonus money regardless of the gambler's outcome. As expected, the brain responses of the gamblers and spectators in the first situation mirrored one another; in the second their responses opposed one another.

But the results from the third condition were most surprising.

When gamblers lost and showed the characteristic ERP, the brains of neutral spectators reacted as though they had lost money, too. "You have some sort of response even when you are not invested in the task," Marco-Pallarés says. "What we know from several studies is that when you are the performer and you lose, you have a very clear event-related response. What we saw was that in the neutral condition there was a very similar ERP even when you weren't actually losing money yourself."

Marco-Pallarés is not sure why the finding is significant for losses, but not gains. He suspects that two competing neural networks negotiate how our brains react to watching others gamble. "There's an empathic system that responds in the same direction as the other person and also another system which only values your own outcomes," Marco-Pallarés says.

Although the new study did not directly address gambling addiction, its findings may be relevant for compulsive gamblers. A recovering addict who watches a poker tournament on television or sneaks off to a casino just to observe others gamble may reactivate the same neural systems that encoded their addiction in the first place, putting them at risk for relapse. The more general implication, which extends a growing body of research, is that even when we are spectators—whether we are watching sports, a movie or a game of blackjack—our brains take on the role of the performer.