By Janet Spencer
The more research is done, the clearer it becomes there isn’t always a clear line between being left-handed and right-handed. Are you a lefty, righty, or something in between?
LEFTY OR RIGHTY?
• The language center in the brain is located in the left hemisphere for about 99% of right-handers. The original theory was that the brains of lefties and righties would be mirror images of each other, and therefore the language center would be located in the right hemisphere for most left-handers. Surprisingly, the invention of the MRI and fMRI proved this to be untrue; the language center is located in the left hemisphere for about 70% of lefties.
• Those who favor their right hand also tend to favor other body parts on the right side of the body to a certain degree: 80% prefer their right foot (when kicking a ball); 70% their right eye (when looking through a telescope); 60% their right ear (when listening on the phone). The split is not the same with lefties, however: 40% favor their right eye instead of their left, and about half are right-footed.
• President Gerald Ford was right-handed whenever he did things while standing up, such as throwing things or playing a sport, but he was left-handed when doing things while seated, including writing and eating.
LEFTY OR RIGHTY?
• Babe Ruth wrote and ate with his right hand but batted and pitched left-handed. In fact, research indicates that up to 30% of left-handers write with their left but throw with their right. Similarly, Ronald Reagan used his right hand for forks and pens but twirled the guns in his movies with his left. When he once threw out the first pitch at a baseball game, he used his right hand, and the pitch went wild, landing in the stands.
• This is typical for ambidextrous people, who tend to divide tasks between hands. These people might more accurately be called “mixed-handed.” Truly ambidextrous people can perform all tasks equally well with both hands, whether they are opening jars, drawing a picture, dealing cards, shaving, or striking a match. Experts estimate that only 1% of the population is fully ambidextrous, using both hands equally well.
• Left-handed people tend to have an advantage in some competitive sports such as boxing, tennis, fencing, volleyball, judo, and karate, perhaps because their right-handed opponents are accustomed to playing other right-handed people and are surprised when some moves come “out of left field.” However, one neuroscientist theorizes that left-handers get their edge because visual processing, movement control, and three-dimensional planning are all located in the same hemisphere, whereas a righty has to coordinate information between the left and the right hemisphere. This process would only take a few milliseconds, but it could explain why lefties have an advantage.
• More than a third of Major League baseball pitchers are lefties, a rate three times higher than the general population. Additionally, 49% of top hitters in baseball have been left-handed. On the other “hand” only 4% of top golfers throughout history have been left-handed.
LEFTY OR RIGHTY?
• Several tests determine how strongly a person is either left- or right-oriented. Designed in 1971 by neuropsychologist Richard Oldfield, the Edinburgh Handedness Inventory measures just exactly how left- or right-handed a person is. Given a list of typical tasks, respondents are asked if they perform each job with the left or right hand or both: using a spoon or toothbrush, writing, throwing, etc. Many people demonstrate a mix of using both hands.
• The Purdue Pegboard test consists of two parallel rows of 30 holes. A dish at the bottom holds 30 pegs that fit the holes and 30 metal donuts that fit on top of the pegs. Test subjects put the pegs in the holes and then place the donuts on top of the pegs as quickly as they can, first using their dominant hand and then using the other. A researcher stands by with a stopwatch to chart the results.
• One unusual evaluation involves a virtual reality environment where a target constantly moves. Test subjects try to hit the target with a cursor, first using one hand and then the other, all while being immersed in the virtual reality world where they cannot see their hands. During the first session, researchers ask them to focus on speed. The second time around, they are asked to focus on accuracy. Test after test shows that the dominant hand performs better in speed tests, while the non-dominant hand consistently displays superior accuracy.
• People who are neurologically or developmentally disabled tend to be inconsistent with which hand they use. This is particularly true if they never learn to write.
• A 2013 study published in “Psychology Today” examined 119 diverse animal species, looking for signs of limb preference. Can crabs be right- or left-clawed? Can turtles? Or is this something unique to humans?
LEFTY OR RIGHTY?
• Researchers found that 51% of species studied exhibited a definite preference for which limb they used most. However, 32% of species studied failed to demonstrate the species-wide preference so prevalent in humans. The other 68% did. For instance, Japanese blue crabs crack shells almost exclusively with their right claws. Pacific leatherback turtles show a strong preference for their right flipper when burying their eggs. Parrots prefer their left foot for picking up objects 90% of the time.
• A 2015 study funded by National Geographic showed that by far the majority of kangaroos are left-pawed. Another study found that the red-necked wallaby, a marsupial, demonstrates a definite hand preference when walking on two legs but not when on all fours. Even the octopus has a favored arm among the eight it has to choose from, while also exhibiting an absolute preference for which eye it uses. Cats, dogs, and most other four-legged species are split 50-50.
• Mice tend to have a 50-50 split when it comes to preferring one paw over the other. One research project attempted to deliberately breed a line of left-pawed mice by allowing only pairs of left-pawed parents to reproduce. Even after 15 successive generations, each newborn mouse still had a 50-50 chance of being left- or right-pawed.
• One researcher studied fetuses in the womb, tracking which thumb they sucked. They took 1,000 ultrasound scans of 75 infants and followed those children until they reached the age of ten. Of 60 infants who sucked their right thumb in the womb, 100% grew up to be right-handed. Of the 15 who sucked their left thumb, ten were left-handed and the other five were right-handed. This still stands as one of the most accurate predictors of the handedness of a yet-unborn child.