If you are looking for a winning edge over your opponent in a high-stakes card game, the eyes may have it.
Psychologists have found that it is possible to tell whether a blackjack player is holding low or high-value cards by watching whether their gaze flicks to the left or to the right.
The study adds to evidence suggesting that when people are totting up numbers in their heads they give off tell-tale signals with involuntary and almost imperceptibly small eye movements.
Researchers at Colorado College and Emory University in the US recruited 58 people to play a computer version of blackjack. The objective of the game is to hold a hand of cards with a total value that is closer to 21 than the banker’s hand, but not above that total.
At the start, each player is dealt two cards. In every round they must decide whether to take another card from the deck or to stay with their current hand.
In the experiment the players had only three seconds to make their choice, forcing them to carry out rapid, if straightforward, mental arithmetic.
Previous studies have indicated that most people visualise a “number line” when they are doing this sort of mathematics, instinctively looking slightly to the left when subtracting and to the right when adding.
Writing in the journal Psychonomic Bulletin & Review, the American researchers said that when players’ hands were particularly low, they tended to gaze briefly and very slightly to the left. As the value rose towards 21, they looked a little more markedly to the right. These changes usually amounted to less than a degree of movement, however, meaning that it would take an exceptionally sharp-eyed gambler to spot them.
Kevin Holmes, assistant professor of psychology at Colorado College, who led the study, said it suggested that people tended to “ground” the abstract ideas of numbers in an imaginary space.
“Whether our findings will help blackjack players in real life has to be investigated,” he added. “Perhaps, following training, observers could rely on gaze patterns to infer hand value.”
Adam Kucharski, a statistician from the London School of Hygiene and Tropical Medicine and the author of The Perfect Bet, a book on the mathematics of gambling, said that the research was interesting but probably of limited use in card games.
“Unfortunately it won’t help gamblers much, because in blackjack players receive their cards face up,” he said. “And in poker, where cards are hidden, it’s not just the overall total that is important. A few casinos offer blackjack with the cards dealt face down, but this won’t give players an advantage as they’re only playing against the dealer — and if anything it makes the game harder, because you can’t count cards.”