Sunday, October 11, 2009

Infant Handedness: Baby Field Notes a Lefty?

A greater preponderance of left-handed U.S. Presidents aside, it has me concerned, a little, that Baby Field Notes might turn out to be a lefty. She's showing what I would call a strong preference for sucking her left hand, moving her left hand more, and holding things longer with her left hand.

The first question I had was whether there's any research to suggest that early hand preference correlates with handedness later. I'm still doing the research, but so far I've turned up some interesting stuff, all published in reputable journals like Developmental Psychobiology and the International Journal of Primatology.

Handedness is associated with brain lateralization and specialization, meaning that the two hemispheres are not exactly alike. The right and left hemispheres execute different functions. For example, most people process language in their left hemispheres. Spatial reasoning, such as mental rotation of objects, is processed in the right hemisphere. Although it's not a perfect relationship, the vast majority of right-handers (90%) process language in their left hemispheres, but only about 70% of left-handers do. A higher proportion of left-handed people process language in the wrong hemisphere, or both hemispheres. It's also said that they are more likely to be dyslexic.

Nonhuman primates are generally not thought to have much language capacity (there are exceptions!). They are also thought to not show much evidence of brain laterality, i.e. their cerebral hemispheres are more symmetrical in function and do not show a left hemisphere specialization for language (there are exceptions!). Furthermore, they are not thought to show a hand preference, i.e. they don't preferentially grasp or manipulate stuff their right hands (there are exceptions with this too!).

What all this means is that other apes don't have the amazing language abilities that humans have because they don't have the brain circuitry specialized for such a complex task and their lack of hand preference is one piece of evidence for that. However, I think that there is plenty of evidence that other apes have some language capacity and that it's likely early human ancestors (6 million years ago) also had language capacity. The human ability to write and recite nursery rhymes didn't just appear out of nowhere, it built upon earlier capabilities.

Left-hand preference may be just one symptom of something gone haywire in brain circuitry regarding language development given the links between the hemisphere dominance, handedness and language processing. In other words, it's not too surprising that more lefties would have language difficulties and I hope that Baby Field Notes doesn't! Language stuff aside, it would make life a lot easier for her to not have to deal with the hassles that lefties encounter.

A good example would be the rotary paper cutter we have. It, like the vast majority of paper cutters, is set up for right handers. The blade is on the right side and the grid and platform to rest the paper on is to the left. For a left handed person to use it, they would have to either operate the blade with their clumsier hand, or, they'd have to hold the paper with their right hand and reach across their right wrist and hand to grasp the arm or blade to cut the paper with their left hand — a recipe ripe for making a mistake and winding up injured.

Speaking of language I find it interesting that the word dexterous, meaning nimble or skillful, comes from the word dexter, which means right. The dexter hand is the right hand. In contrast, left in French is gauche, which in English means clumsy or boorish. Compliments that have a subversive, not so nice element to them are left-handed compliments. I'm just saying, left handers don't just die earlier (as research has found), our whole language schema paints them in a poor light.

However, left handedness/right brain dominance is also associated with being gifted analytically, particularly in mental rotation and three-dimensional problem solving.

In an effort to find out whether early left hand preference is associated with being a lefty, I skimmed a bunch of journal abstracts, and although I haven't yet found an answer, I did learn some other interesting stuff.

At just 5 months gestation, fetuses already show brain lateralization. Using ultrasound imaging, researchers measured the size of both lobes of the brain of around 100 fetuses and found that their left hemispheres were larger than their right hemispheres. Also interesting is that the girls had larger brains.

Fetuses suck their thumbs in utero, no surprise there, but they also show a preference for sucking their right thumb and this can show up as early as 15 weeks of gestation. Also, research on some primate species, including both monkeys and two kinds of apes (bonobos and chimps) has found that they have a nipple preference — left — which is also associated with a preference for turning their heads to the right, which would be toward the left breast when being carried and while suckling. What's noteworthy too, is that nonhuman primates and humans both show a bias for left-handed infant carrying and cradling.

Early on, BFN preferred the right boob, the atypical pattern. I also have a strong preference for carrying her and cradling her in my right arm. Mr. Field Notes does it in the more usual primate fashion — with his left arm — and was the first to observe that I don't. So I guess I am odd and maybe Baby FN is too.

In any case, Baby Field Notes may indeed turn out to be a lefty, and it's not likely I will be able to change that if she is. Handedness is not learned, a plethora of research suggests. Instead, it is "a spontaneous expression of the developing nervous system unaffected by the environment," as Dr. Johanna de Vries put it best.

However, other researchers, such as William Hopkins, point out that behavior can influence brain development, so use of the right hand can theoretically cause the brain to develop asymmetrically. [I think there's some merit to that, but how likely is the preference of right hand use to be just chance?] I think it's more likely hand preference is genetically determined and there's a good chance that no amount of me putting things in Baby Field Notes right hand will change anything if she is indeed a lefty.

My intuition is also that she is likely to be a lefty, given her hand preference now.

9 comments:

Shana Lee said...

Not sure if it will make you feel better or worse, but I'm a lefty. And my mother tells me I reached for things with my left hand from the beginning. Yes, I may have some mild dyslexia (thank the lord for spell checkers!), but I also majored in Spanish in college so clearly I overcame language issues. :)

It can be frustrating to be a lefty in a right handed world, but I also think it's made me more creative since I have to think about things more. And I don't believe that's such a bad thing.

Field Notes said...

Thank you for this, Shana. It does make me feel better, a little. She's not reaching for tings just yet, and when that happens, I will be really interested to see. It's interesting that you think being a lefty prompts you to be more creative. I could see how that might happen and hadn't thought about it in that way.

Virginia Burnett said...

My dad, my daughter and I all exhibit a certain degree of ambidexterity. We all write with our Right hands but there are certain things we each do better with our left hands (for instance, my dad bowls and bats left handed.) I also have some dyslexic behaviors (tendency to transpose numbers) but we all have very strong language capabilities.

I also know a leftie who struggled with severe dyslexia in high-school who has managed to grab that disability by the throat and overcome. She is incredibly well read, intelligent and speaks several languages, including ASL.

My sister-in-law is left handed and is incredibly creative and accomplished.

It will all come down to how important language is in your household and how you assist her in approaching any challenges her handedness presents. I know that aside from her frustration with teachers who wanted her to switch to her right hand, my sister-in-law is quite hapy to be a lefty and I've always felt that my ability to use both hands with a similar level of skill has helped my in my art. :)

Field Notes said...

Thank you too, Virginia!

I think I'm just being a classic overly concerned parent about this at some level.

Science Bear said...

The majority of my maternal family is left-hand dominate. Everyone except my immediate line (mother, grandmother). All of my aunts and uncles have stated some form of the problems you mentioned. The good news, they all excelled in math and science.

I'm the abnormal one for my immediate family, in that I started off as a true amhbidextric. I switched hands while doing activities and would get punished as a result. I show a strong preference for my left hand in certain areas (bowling, batting, playing pool or the guitar, etc), but write and eat with my right hand.

I have retained the ability to switch between hands for most activities, and write legibly with my left hand, but much slower (so I tend to stay with my right).

If you are interested in pediatric brain lateralization, look up the work of Thomas Badger and his "Beginnings" project. It is a longitudinal observational study starting at one month of age and when I left the program the children were 6 years old (should be around 8-9 now).

The study mentioned above also shows the different influences infant feeding has on development and is, to my knowledge, one of only a few sites doing this type of comprehensive analysis. If you have any questions about what they do, let me know!

Anonymous said...

When I read this post, my first thought was, really? I had no idea left handed people were more prone to dyslexia. I'm left handed and I was an English major, speak fluent French, paint very well and also majored in BioAnthro. Never had any learning disabilities, and (not to too my horn TOO much) I graduated in the top of my class in both high school and college. I think being left handed, if anything can be extremely beneficial. So don't worry!

AmandaMay said...

I am also lefthanded, and am quite happy to be so actually. I did write backwards as a small child, completely backwards as in right to left with the letters backwards as well, but that disappeared on its own and I was way ahead of my classes in reading by kindergarten and first grade. I did quite well in Spanish and German throughout elementary and high school and had very high marks for research and creative writing in college.

I think part of making left-handedess work is not making too much of it. I learned to use scissors with my right hand because otherwise they did not work and no one went out of their way to find good lefthanded scissors. The only time I am worried about being left handed is when I am eating in an Asian or Indian restaurant, so I have practiced eating right handed just in case :)

It is interesting to read your research into the behaviors of lefthanded vs right handed primates. It reminds me of the joke (possibly not actually correct, but amusing to me) that since the left side of the brain has more control over the right hand and the right side over the left hand, only left handed people are in our right minds!

Field Notes said...

Thanks for your comment, AmandaMay. I like that -- the right minds =D

I hadn't thought about the forbidden left-handed eating custom in many cultures. I will have to remember that since we do plan to travel a lot with her!

Kanisha said...

well you could end up just confusing her entirely. As a leftie I was taught to use knife and fork in the "correct" right handed manner whilst I do always use a knife in my right hand with a fork it gets naturally transferred to my left for buttering with a knife. complications then with using a spoon in my left hand for soup but in my right when also holding a fork for eating pasta.... if she is naturally left handed enjoy her allow her to experiment. I use scissors in both my left and right equally well, as well as many other tools where working on both sides is an advantage. I am a natural leftie in a right handed world and have found my own route through lifes technicalities I'm also bilingual ( learned a second language as an adult ) and also as a result of growing up in the middle east can quite happily eat food with my right hand when its required for good manners but I prefer chopsticks in my left hand. Never seen it as a problem except I was never given the allowances for hand writing that would have made life a little simpler. Often its how I get taught I serve with my right hand and play tennis with my left as I was taught to serve by a right handed teacher.... If she is naturally left handed sobeit but its rarely been anything for me except one of life quirks.