Finger counting habits modulate spatial-numerical associations.

This study explored the contribution of finger counting habits to the association of numbers with space (the SNARC effect). First, a questionnaire study indicated that two-thirds of 445 adults started counting on their left hand, regardless of their handedness. Secondly, a group of 53 "left-starters" but not a group of 47 "right-starters" showed a SNARC effect in a parity task. A significant difference in the strength of the effect between groups suggests that finger counting habits indeed contribute to the association between numbers and space in adults.