Friday, July 12, 2013
Right-handed or Left-handed? How Early Can You Tell?
How Do Babies Become Right or Left Handed?
Scientists do not fully understand how babies end up favoring one hand over the other. A few ideas have been tested related to babies’ positioning in the womb. Because of the limited space and the position of maternal organs, developing babies end up looking to the right more often than to the left. This means that they are more likely to see and become familiar with their right hands. Another idea relates that there is more likely to be space in the womb to move the right hand versus the left. If one hand is easier to move around, it may end up as the preferred hand. Some scientists have focused on factors influencing handedness after the baby is born. Typically, newborns do look to their right more often than their left and they will work to move the hand they see. This may result in earlier voluntary movement of the right hand. Another theory relates to the fact that babies watch and learn from their parents. Babies notice which hands are used to feed them, play with them etc. This theory may partly explain why left-handedness tends to run in families.
So, the current thinking is that most babies become right-handed because of several circumstances that slightly but consistently increase in the likelihood that they will see, explore, and use their right hands both prenatally and postnatally. We lefties either didn't have these experiences or reacted to them differently (perhaps that's where the brain differences come into it).
How Early Can you Tell if a Baby will be Right or Left Handed?
Many parents start to imagine that their baby is left- or right-handed based on the percentage of time their 4- or 5-month-old reaches awkwardly with one hand or the other for an object that is held in front of them. But simple one-handed grasp actions are easy to do with the non-dominant hand (you do this every day) so trying to identify the preferred hand so early isn’t likely to be very predictive (at least not of left-handedness because nearly all babies end up right-handed). Handedness becomes more predictable when babies start to use both hands to explore objects. Older babies will use one hand to grasp and the other to keep objects steady or to manipulate them. When they start to play with toys in more complex ways (stacking, pulling them apart, putting them in and out of containers), they are more likely to use a dominant hand. Babies tend to be older (18 to 24 months) before handedness becomes more consistent. No matter what age your baby starts to prefer one hand over the other, there are a couple of things you should know. First, handedness is really a continuum, meaning that most babies can use both hands but they tend to use one hand more effectively than the other. Some people rely on the preferred hand for nearly everything, others can use both hands for most tasks. Handedness in adults and older children seems absolute only because of habits and more practice doing daily activities like eating and writing with one hand. Second, researchers have found that babies are less likely to show hand preference when they are learning new skills. That means that you might see your baby using one hand much more often than the other until he starts doing something new (like standing) and then he might use both hands equally until he masters the new skill.
Fagard J. The nature and nurture of human infant hand preference. Ann. NY Acad. Sci. 2013; 1288: 114-123.
Michel GF, Babik I, Sheu CF, and Campbell JM. Latent classes in the developmental trajectories of infant handedness. Dev Psychol. 2013; June 17 Epub.
Nelson EL, Campbell JM, Michel GF. Unimanual to bimanual: Tracking the development of handedness from 6 to 24 months. Inf Beh Dev 2013; 36: 181-188.