Blog 7 Its not left that’s right!?

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The other day in the maclab while daydreaming my mind wandered off and began to think about potential topics for my blog, scanning my eyes around the room I could’t help to notice how pretty much everyone was right handed. It got me thinking about the potential differences between left and right handers cognitively in addition to their academic performance. It is estimated that 85 percent of individuals are right-handed with the remainder being left handed. In schools left handed pupils are often discriminated  against in particular during the ’70s and ’80s, parents often forced their left-handed children to use their right hands. But from looking into the definition of left handed globally it has negative connotations, also lefties often feel out of place in right handed world so often become ambidextrous in order to adapt

Cross culturally the meaning of left is certainly seen as negative. The Latin meaning for left is sinister. In French an individual seen as unskillful is called “gauche” meaning left. In German someone is given the name ‘linkisch’ (meaning ‘leftish’) if they are either weird, odd or even nasty in an antisocial sense. Right, in Dutch is recht but it also means straight, privilege (as in human rights),Link means left, stupid, awkward, but also keen, skilled. The Gaelic (Irish) word for lefthanded is “Ciotach”. It has two imports as well 1) lefthanded and 2) Awkward or difficult. In Welsh left is ‘chwith’, which also implies being strange.

But research suggests that left handedness may not be as negative as the definition suggests. Left-handed individuals are quicker at processing multiple stimuli than righties for example tasks like talking and driving simultaneously. Left handed individuals are more bicerebral. They become faster at tasks because they have to use both sides of the brain more.” Through adapting to a right handed world.

Another area of specialization in left handed people is that of sensory-data processing: Typically, information received on the right side of the body (the right eye, or the right ear, for example.) goes to the left hemisphere for processing, and information received on the left side goes to the right hemisphere. Eventually, the brain combines the processing results from both hemispheres to form what we consciously perceive visually and through our audition.

There is a distinct link between handedness, brain lateralization and anatomy. Lateralization of speech is related to handedness. 95% of righthanders have speech lateralized in the left hemisphere, with only 2% of left-handers exhibiting this (Hellige, 1990). Additionally, Driesen and Raz (1995) established that the corpus callosum was bigger and better connected in left-handers.

Experts also theorize that left-handed people could perform better mentally as they become elderly and general brain processing starts to decrease in speed: with an enhanced ability for one brain hemisphere to quickly back up the tasks of the other, left-handed seniors could retain mental quickness for an extended period of time in comparison to their right-handed counterparts.

Regarding cognitive skills in left handed individuals, the research is mixed. (Eglinton and Annett, 1994) discovered a “small but reliable increase” of dyslexia among left handed individuals (Eglinton and Annett, 1994). Certain studies have discovered average performance in high school is lower for left-handed students (for example, Williams, 1987), while additional studies have discovered conflicting evidence for example Faurie, Vianey-Liaud, and Raymond (2006) found handedness to be positively correlated with school achievement and leadership skills for boys, while the correlation was negative for girls. Typically, studies show discrepancies in cognitive skills that are in favour of right-handed individuals (Hardyck and Petrinovich, 1977; Porac and Coren, 1981). But again there is research to prove otherwise Benbow (1986) established that gifted youths were two times as likely to be left-handed than individuals in the control group. Geschwind and Galaburda (1987, p. 98) determined that “non-righthanded populations are over-represented in all populations with high talent” (McManus and Bryden, 1991).

In addition it has been put forward that discrepancies may be due to cognitive styles rather than cognitive abilities. Coren (1995) approximates that the link between handedness and two forms of thinking- convergent (“a fairly focused application of existing knowledge and rules to the task of isolating a single correct answer”) and divergent (“moves outward from conventional knowledge into unexplored association”). Divergent thinking is proved to be positively associated with the extent of left-handedness, but just for males.

Lastly left handed individuals may not only fair better cognitively but once they have received their education or relevant qualification they may earn more. A noteworthy increase in earnings for left-handed men with high levels of education was discovered. This positive wage effect is strongest among those who have lower than average earnings relative to those of similar high education. Coren (1995) discovered that “divergent thinking” is more customary with male left-handed individuals. If it is this differential cognitive style that is the source of higher earnings for University educated left-handed men, it would justify why it is not found in women.

 

 

 

 

 

 

 

 

References

http://www.indiana.edu/~primate/brain.html    http://www.indiana.edu/~primate/refs1.html

http://www.telegraph.co.uk/science/science-news/5963820/Domestic-cats-can-be-left-or-right-handed-scientists-find.html

http://www.iched.org/cms/scripts/page.php?site_id=iched&item_id=lefthand_righthand

http://health.howstuffworks.com/human-body/parts/left-handed.htm

http://www.humanforsale.com/left-vs-right.asp

http://news.softpedia.com/news/Left-handed-people-think-faster-than-left-handed-people-42445.shtml

http://www.scientificamerican.com/article.cfm?id=what-causes-some-people-t

http://www.sciencedaily.com/releases/2010/01/100128101901.htm

http://www.indiana.edu/~primate/lspeak2.html#educators

1 http://dspace.lafayette.edu/bitstream/handle/10385/669/Ruebeck.Laterality-vol12-no2-2007.pdf?sequence=1

2 http://0-www.tandfonline.com.unicat.bangor.ac.uk/doi/pdf/10.1080/713754398

http://jhered.oxfordjournals.org/content/8/5/214.1.full.pdf

http://en.cnki.com.cn/Article_en/CJFDTOTAL-TIRE200702001.htm

http://0-www.tandfonline.com.unicat.bangor.ac.uk/doi/abs/10.1080/713754398

http://0-www.springerlink.com.unicat.bangor.ac.uk/content/pt7x710j3141481k/fulltext.pdf

 

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6 responses »

  1. Interesting as always Eliza! One thing I find particularly interesting is that lateralization in relation to handedness is more strongly evidenced in males, particularly when processing emotion (Bourne,2008).
    Having left handed relatives seems to be beneficial too, even in females. Right-handed females who did or didn’t have biologically close left handed relatives were compared in spatial tasks. Those with left-handed relatives outperformed those that didn’t, as they appeared to not rely on verbal strategies (D’Andrea & Spiers ,2005).
    It seems if you have a leftie as a relative- as a female, you are less likely to depend on the left hemisphere to solve spatial problems, as most females do (Casey & Brabeck, 1990). This infers that there is stronger interhemispheric processing in these individuals, which has been associated with superior episodic memory (Christman & Propper,2001).
    So left is good, even if you are just related to someone who is left handed!

    Bourne,J.V (2008) Examining the Relationship Between Degree of Handedness and Degree of
    Cerebral Lateralization for Processing Facial Emotion
    Neuropsychology ,22 (3)350 –356 0894-4105/08 doi: 10.1037/0894-4105.22.3.350

    Casey, M., & Brabeck, M. (1990). Women who excel on a spatial task:
    Proposed genetic and environmental factors. Brain and Cognition, 12,
    73– 84. doi: 10.1016/0278-2626(90)90005-9,
    Christman, S. D., & Propper, R. E. (2001). Superior episodic memory is
    associated with interhemispheric processing. Neuropsychology, 15, 607–
    616. doi: 10.1037/0894-4105.15.4.607
    D’Andrea, E.A & Spiers,M.V ,2005The Effect of Familial Sinistrality and Academic Experience on Cognition in Right-Handed Women.Neuropsychology 19 (5), 657– 663
    doi: 10.1037/0894-4105.19.5.657

    • Thought provoking point Amy, thanks for the comment.

      Regarding having left handers in your family and the genetic influnence of left handedness a Scientific American Mind article states that two-right handed parents have a 9.5 percent chance of having a left-handed child. A mixed couple, with one left handed individual and one right handed individual, have approxiamtly double those chances. Yet, two left-handed individuals in a couple have a 26 percent chance of producing a right handed child (Detlef, Linke and Kersebaum 2005).

      But (Annett, 1970) said that no single gene predicts handedness, yet, left-handedness has potentially proved to be a heritable trait (McManus 1991). On the other hand, at the period of fetal
      development, a particular molecular factor aids the strengthening of the brain’s left hemisphere, thereby increasing the likelihood of right hand dominance, as the left side of the brain is in control of the right side of the body, and vice versa. With the few individuals who don’t have this trait,
      handedness forms totally by chance. Yet twin studies make the theory more complicated. One out of every five sets of identical twins has one right-handed and one left-handed individual, in spite of the their identical genetic make up. Thereby Genes, cannot be fully responsible for handedness.

      Nature may predict if a child will be left-handed or righthanded, but environment may also have a bearing on genetic predisposition. A child may pick up their parents’ handedness even if it is against their individual biological make up for instance.

      …………..Again is it back to the old age debate of nature versus nurture!

      http://www.fulviofrisone.com/attachments/article/439/Scientific%20American%20-%20Mind%20-%202005%20-%20Volume%2016%20-%20Number%2004%20-%20Memory%20Upgrade.pdf

      http://www.scq.ubc.ca/the-fighting-hypothesis-stability-of-polymorphism-in-human-handedness/

  2. I’d never thought that the differences between left and right handed people could be so pronounced. Looking into it, I found that in 1985 Witelson found that left handed corpses had larger corpus callosums than right handed people. Schmidt, Oliveira, Rocha, & Abreu-Villaca (2000) suggested this was the reason that left handed men performed better at the Grooved Pegboard Test.

    Witelson, (1985): http://www.sciencemag.org/content/229/4714/665.short

    Schmidt, Oliveira, Rocha, & Abreu-Villaca (2000): http://psycnet.apa.org/psycinfo/2000-14257-009

    • According to research by (Randerson, 2001) in The New Scientist Ambidextrous tendencies may lead to better memory.

      For example if one has a close left-handed relative this influences right-handers memory and allows them to better recall events over individuals from just right-handed families. There are negative factors however, for instance individuals of these ambidextrous families may be margonally impaired regarding their aptitude to remember facts.
      Also if you have a left-handed sibling or parent your brain make up somewhere is between a pure ‘lefty’ and a pure ‘righty’.

      Specifically, Stephen Christman and Ruth Propper at the University of Toledo, Ohio say if you have a ‘lefties’ in your family you will have a bigger corpus callosum. Which increases your ability at particular memory tasks, but decreases other tasks. This involves two types of memories, eposodic and semantic memories. Episodic memories involve a situation that is separate from the information itself – for instance, where you positioned your bike or where you put your wallet, Semantic memories on the other hand is knowledge that you just have, like that the capital of France is Paris.

      Coming to a clear conclusion and results requires further research. But Christman believes that it may involve the roles that varying brain hemispheres play in memory. He thinks the information is generally kept in the left hemisphere, while the place and time information is stored in the right. These factors are important for episodic memories, so Christman believes individuals with a bigger corpus callosum joining the two hemispheres – like people from ambidextrous families – will perform increasingly well at these tasks. Semantic memory only needs, one hemisphere, so potentially individuals with less ‘connections between the hemispheres have less interference and perform better’.

      http://www.anythinglefthanded.co.uk/research/lefthanded-research.html

  3. Vallortigara (2006) asks a good question “ why are left handed and right handed people not equal in numbers?”. On explanation for lateralization is that it frees up one hempishere of the brain allowing more than one task to be completed at the same time and promoting efficiency within the brain(Denenberg, 1981). So if people are left handed then maybe they are freeing up the right hemisphere to allow different processes to occur. However is this an advantage?. Well it may be shown by some of the research you found that left handed people do better cognitively. Vallortigara also states that left handedness has a genetic link; therefore to me suggests being left handed cannot be bad because otherwise it would have been lost through evolution. It is positive that you have found benefits to being left handed because it explains why it has not been lost; but i still ask the same question as Vallortigara that why are left and right handed people equal in numbers?

  4. Yes thats an interesting point rgadd and in researching for my blog I came across some current explanations that may go some way to answering Vallortigaras (2006) question.

    Handedness is not set in stone at birth. Normally it is influenced over time, by external factors and the environment in which the child grows up in. So as I metioned above during the 60s and 70s a child may have leaned towards using their left hand but this would have been very much discouaged and therefore would disapper over time. As I mentioned in my comment to Amy there may certainaly be a genetic predisposition to left-handedness or right-handedness, but handedness is malleable by the environment (Detlef, Linke and Kersebaum 2005).

    According to the genetic theory that many scientists support, left-handedness is a recessive gene, and right-handedness is dominant. This supports why left-handedness occurs more often in a family that have older relatives that are left handed.

    Marion Annett a scientist thinks that the majority of people exhibit a “right shift” factor. ‘This factor disposes it’s carrier to be right-handed. When the gene is absent, the individual may be either right-handed or left-handed’. She examined this idea by interviewing children who had right and left handed parentals. As the parents were left-handed and therefore did not have the right-shift factor, the children should not exibit it too. Annet analysed the speed that children could carry out a peg-sorting task. The results indicated that 50% exhibited more favourable results on their left hand, and 50% more favourable results with the right. These findings support Annets hypothesis ‘that the hand preference of those without the factor would be determined by chance’.

    http://molly.kalafut.org/lefthanded/lefthanded.html

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