Springer
Blackjack players who hold high-value cards tend to glance
fleetingly to the right, whereas those with a lower-value hand do so
spontaneously to the left.
This is according to research on aspects of mental
arithmetic, led by Kevin Holmes of Colorado College in the US. The findings are
published in Springer's journal Psychonomic Bulletin & Review.
Research suggests that you can actually judge something about
the mental arithmetic that people are doing silently in their heads based on
involuntary tell-tale signs they produce.
For example, when pointing to an
arithmetic solution on a visually presented number line, participants are
biased leftward on subtraction problems and rightward on addition problems.
Holmes and his colleagues, Vladislav Ayzenberg and Stella Lourenco of Emory University, conducted two experiments to find out what role attention plays in such a mental number line within a real-life setting.
They
turned to blackjack, a game in which players must repeatedly decide whether to
stick with the cards in their hand or risk a "bust" by taking another
card.
Such decisions can only be done wisely if players are able to mentally
sum up the values of successive cards, and thereby compute the total value of
their hand.
During the two experiments, a total of 58 participants played a
computerized version of blackjack.
New playing cards were presented to them in
succession in the middle of a screen. Participants then had to decide whether
to discard a card or to keep their hand as is, which inevitably involves
mentally adding the values of the cards.
In the process, Holmes' team analyzed
in which direction participants moved their eyes while they were doing mental
math.
It was found that participants' spontaneous eye movements along
the horizontal axis reflected the overall numerical value of their cards.
Participants tended to look toward the left side of the screen when they had
smaller-value hands, while they looked toward the right side when they had
larger-value hands.
These effects were driven by the total value of the cards
that a player had in the hand. It was not influenced merely by the number of
cards that a player was holding, nor the value of the card he or she was just
dealt.
"Whether our findings will help blackjack players in real
life still has to be investigated," said Holmes. "The relatively
small differences in absolute gaze position we found here may be undetectable
to the naïve observer. Perhaps following training, observers could rely on gaze
patterns to infer hand value."
