Poker pros’ arms betray their hands

No bluff: In high-stakes matches, a poker face may not be good enough. Players may have to develop “poker arms” as well.

When shown two-second video clips of the arms and hands of top players making bets in the World Series of Poker, college students did well at judging who was playing a strong hand and who wasn’t, say psychology graduate student Michael Slepian of Tufts University in Medford, Mass., and his colleagues.

But when viewing videos of only poker pros’ upper bodies or faces during bets, students couldn’t correctly predict whether players held good or bad cards, the researchers report Sept. 12 in Psychological Science.

In other words, experienced players’ poker faces gave away nothing. “But professional poker players’ arm movements enabled untrained observers to decode poker-hand quality,” Slepian says.

Observers often rated poker players who held good cards as having moved their arms smoothly when pushing chips forward to make bets; bluffers moved their arms somewhat awkwardly. It’s not known, though, whether poker players whose arm movements were rated as smooth really slid chips forward more gracefully than their opponents did.

Slepian’s study adds to preliminary evidence that the ways in which people move provide clues to what they’re thinking, remarks psychologist James Kilner of University College London.

A 2012 study coauthored by Kilner found that volunteers who responded to a lab task by moving a marble to one of two holes on a board did so more quickly when they were confident in their responses. In addition, observers consistently rated rapidly responding volunteers as confident in their decisions.

In the new study, Slepian and his colleagues divided 78 college students into three groups. Each group watched 20 video clips of big-time poker players placing bets. Clips showed the players’ heads and arms, heads only or arms only. Study participants guessed at the quality of each poker hand on a scale from 1 to 7, from “very bad” to “very good.” The researchers then compared these ratings with each player’s statistical likelihood of winning, as provided by the World Series of Poker.

None of the participants played poker regularly. Those who had played some poker, however, did best at using players’ arm movements to tell weak from strong hands.

Finally, the researchers found that a different group of 40 students rated poker players who were betting on strong hands as confident and as having smooth arm movements.