Successful gambling, at least in poker and blackjack, relies on a combination of statistical know-how, reading an opposing player’s behavior, and pure luck. Science may not be able to help with your mental math skills or luck, but it may be able to give you a leg up while trying to read someone’s poker face. According to research recently published in Psychonomic Bulletin & Review, a person could be giving away their hand with a simple glance.

There’s been previous research on involuntary signs that reveal what a person’s brain is doing. For example, a person doing a math problem that’s presented on a number line is likely to look left while performing subtraction and right when adding. This is hardly a real life application, though, so Kevin Holmes of Colorado College led a team in conducting an experiment to see if that trick applied to blackjack. The card game, popular in casinos, requires players to decide whether they should stick with the cards they have in their hands or risk a bust by taking a new one. If players hope to do so wisely, they must try to mentally sum up the value of cards that remain in the deck, and in turn calculate the potential values of their own hands.

Blackjack players often do mental math to decide their next move. Pixabay Public Domain

For the experiment, Holmes and Emory University colleagues Vladislav Ayzenberg and Stella Lourenco had 58 participants play a computerized version of blackjack. The computer dealt them new cards in the middle of the screen, after which they decided if they wanted to discard a card or keep their hand. Holmes’ team watched the participants play, analyzing their eye movements while they were making decisions about their cards. They discovered that players’ eye movements tended to reflect the value of their hands: they glanced left when they had smaller-value hands and right when they had larger-value ones.

“Even when controlling for the number of cards in the hand and the value of the card just dealt, the overall value of the hand predicted the horizontal position of participants’ gaze,” the authors wrote. “This suggests that the horizontal eye movements in our task reflect the mental summation of values, not merely the processing of serial order of individual numbers.”

The researchers do acknowledge that there are major differences between the experiment and a real blackjack game, and that such subtle eye movements may be unrecognizable to a casual observer. However, future studies could focus on exploring if players could, with training, use gaze patterns to infer hand value during games with higher stakes.

“Whether our findings will help blackjack players in real life still has to be investigated,” Holmes said in a press release.

When there’s money on the line, odds are players will take any help they can get.

Source: Holmes J, Ayzenberg V, Lourenco S. Gamble on Gaze: Eye movements reflect the numerical value of blackjack hands. Psychonomic Bulletin & Review. 2016.