By Heather Kobayashi
There’s more to being a lefty than just which hand you write with. That sentence may sound wrong to some, but a growing body of research shows a many unexpected differences between different-handed individuals.
In everyday speech, there is seeming equivalence between “right” as opposed to wrong and “right” as opposed to left; however, there are some advantages to being “sinister,” or “gauche,” both originally words for left which have become pejorative in modern language. Left-handers have had disproportionate representation in the White House: including President Obama, 18.6% of US Presidents (8/43) have been left-handed, approximately double the percentage in the general population. Recent research also suggests that left-handers have a more accurate body sense than right-handers: when asked to estimate arm length, left-handed people estimated both arms as being the same length, while right-handed people tended to underestimate the length of their left arms. Similarly, left-handed people estimate that both of their hands are the same size, whereas right-handed people estimate that their right hand is larger. Researchers theorize that this difference indicates a variance in neural networks, the physical pathways of the brain, with right handed people devoting more brain matter to mapping of the right side of their bodies. Left-handed people, instead of having a larger brain map of their left sides, devote neural space about equally to both halves of their bodies–a decidedly less lop-sided approach. In fact, lateralization, as distribution of functions between the hemispheres is called, has garnered attention particularly where handedness is concerned.
Brain lateralization may relate to some of the disadvantages of being a lefty. Geschwind and Behen (1984) found a correlation between left-handedness and a host of immune and respiratory disorders as well as some learning and language disorders. They theorized that the diseases and disorders, brain lateralization, and handedness itself are all due to higher pre-natal testosterone exposure; however, they were also quick to speculate that there are some disorders which have lower occurrence rates among “sinistrals” and cited the higher than average rate of left-handedness in highly skilled professions such as architecture as evidence that left-handed people are not overall less intelligent or healthy. More recent research has cast some doubt on this theory, asserting that the hypothesis itself is ill-defined (Bryden, McManus, and Bulman Fleming, 1994). Geschwind and Behan failed to specify what levels of handedness and lateralization were supposed to correlate on the continuums of both scales and a meta-analysis of psychological research shows no particular support of the 1984 findings. Nevertheless, they still remain heavily cited because no stronger model of handedness has emerged. In addition, studies do show that lefties live, on average, 3 fewer years than their dexterous colleagues (Myers, 2007). This phenomenon may have its roots in–rather than a psychological difference–the greater number of workplace accidents that befall left-handed people because of mechanical systems designed for righties (a more severe form of the “there are no left-handed scissors” phenomenon in my kindergarten classroom). Identical twins often have different handedness, so some factor besides genetics must be in effect, but there is also high heritability of the trait (Myers, 2007). Thus, it remains unclear exactly how handedness, health, and the brain are related.
Then there are the ways in which being left-handed affects not the body, but perspective. In another recent study, researchers asked left-handed and right-handed people to place “good” or “bad” objects into one of two identical boxes. While right-handed people placed the good things in the right-hand box, left-handed people did just the opposite; this tendency was also reflected in product choices. (University of Granada, 2010) It appears that while right-handed people tend to associate rightness with rightness, as it were, left-handed people have the opposite associations. In this way, a simple change in sensory-motor experience seems to override cultural (linguistic) norms and simple spatial properties are linked to abstract concepts.
While some of these behaviors may seem trivial, they all point back to the infinite feedback loop which is the brain: behaviors shape neural networks which further influence behaviors. Neural patterns and pathways, formed by genetics and experience, shape actions both large and small, serious and trivial. Handedness is one of the many ways in which scientists can compare the way that different brains works and how that manifests itself in everyday life.
Association for Psychological Science (2009, November 5). Vast Right Arm Conspiracy? Study Suggests Handedness May Affect Body Perception. ScienceDaily. Retrieved March 5, 2010, from http://www.sciencedaily.com/releases/2009/11/091104152304.htm
Bryden, M. P., McManus, I. C., & Bulman-Fleming, M. B. (1994). Evaluating the empirical support for the Geschwind-Behan-Galaburda model of cerebral lateralization. Brain and Cognition, 26(2), 103-167.
Geschwind, N., Behan, P. O., & Galaburda, A. M. (Ed.). (1984). Cerebral dominance : the biological foundations. Cambridge, MA: Harvard University Press.
Holder, M. K. (2009). Famous left-handers. Retrieved from http://www.indiana.edu/~primate/left.html
Myers, David G. (2007). Psychology (eighth edition in modules). New York: Worth Publishers.
University of Granada (2010, February 2). Right-handed and left-handed people do not see the same bright side of things. ScienceDaily. Retrieved March 5, 2010, from http://www.sciencedaily.com/releases/2010/01/100128101901.htm