Poker players watch for their opponent's tells -- tics and mannerisms that give away the strength of his hand. Scientists have discovered that there is a link between eye movements and our perception of numbers, although this tell is probably too subtle to be useful in Las Vegas.
A team from the University of Melbourne and the University Hospital Zurich asked subjects to speak a random sequence of numbers between 1 and 30; when the next number in their sequence was smaller than the previous one, their eyes would shift leftward and downward. When the next number was larger, the eyes would shift rightward and upward. Interestingly, they also found that a large number shift brought about a large eye shift, and a smaller number shift, a smaller eye shift.
The shifts were identified by taking the average position during the half-second before the subject announced the next number. The study mentioned the "Theory of magnitude," which suggests that the perception of numbers could be tied in our minds to three-dimensional space, as though we were plotting physical movement in response. These findings fit within that theory.
While this wasn't covered in the study, it is interesting to speculate that perhaps a very, very perceptive card player could indeed read the size and direction of a card dealt to an opponent by watching his eyes. Me, I'm wearing shades from now on.
Poker face? Study suggests your eyes tell all