In a 1986 study of students who had scored in the top of their age group on either the math or the verbal sections of the S.A.T., the prevalence of left-handers among the high achievers—over fifteen per cent, as compared to the roughly ten percent found in the general population—was higher than in any comparison groups, which included their siblings and parents. Among those who had scored in the top in both the verbal and math sections, the percentage of left-handers jumped to nearly seventeen per cent, for males, and twenty per cent, for females. That advantage echoes an earlier sample of elementary-school children, which found increased left-handedness among children with I.Q. scores above a hundred and thirty-one.
This spring, a group of psychiatrists from the University of Athens invited a hundred university students and graduates—half left-handed and half right—to complete two tests of cognitive ability. In the Trail Making Test, participants had to find a path through a batch of circles as quickly as possible. In the hard version of the test, the circles contain numbers and letters, and participants must move in ascending order while alternating between the two as fast as possible. In the second test, Letter-Number Sequencing, participants hear a group of numbers and letters and must then repeat the whole group, but with numbers in ascending order and letters organized alphabetically. Lefties performed better on both the complex version of the T.M.T.—demonstrating faster and more accurate spatial skills, along with strong executive control and mental flexibility—and on the L.N.S., demonstrating enhanced working memory. And the more intensely they preferred their left hand for tasks, the stronger the effect.
The Athens study points to a specific kind of cognitive benefit, since both the T.M.T. and the L.N.S. are thought to engage, to a large extent, the right hemisphere of the brain. But a growing body of research suggests another, broader benefit: a boost in a specific kind of creativity—namely, divergent thinking, or the ability to generate new ideas from a single principle quickly and effectively. In one demonstration, researchers found that the more marked the left-handed preference in a group of males, the better they were at tests of divergent thought. (The demonstration was led by the very Coren who had originally argued for the left-handers’ increased susceptibility to mental illness.) Left-handers were more adept, for instance, at combining two common objects in novel ways to form a third—for example, using a pole and a tin can to make a birdhouse. They also excelled at grouping lists of words into as many alternate categories as possible. Another recent study has demonstrated an increased cognitive flexibility among the ambidextrous and the left-handed—and lefties have been found to be over-represented among architects, musicians, and art and music students (as compared to those studying science).
