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History of “left handedness“..! Dr. Tejas

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Handedness..!!

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History of “left handedness“..!

Dr. Tejas

Scheme of presentation

• Introduction & Definition • Assessment• Theories• Myths and Facts• Issues• References

Definition

• Handedness:– Handedness is a better (faster or more precise)

performance or individual preference for use of a hand.

Definition

• Right-handedness 70–90%• Left-handedness 10%• Mixed handedness 30%• Ambidexterity exceptionally rare, – Can be learned.

• Ambilevous or ambisinister

Testing for Handedness

• Asking Questions or Physical Tests• The “Big Three” tasks are writing, eating and

throwing.• Computer mouse• Purdue Pegboard Test

Edinburgh Handedness Inventory

Theories

• Environmental • Developmental• Evolutionary• Genetic

ENVIRONMENTAL THEORIES

• Plato was convinced that the limbs are naturally of equal strength and ability, and that any handedness is culturally imparted.

• In fact, he went so far as to blame left-handedness on inept mothers and nurses who failed to adequately school their children in the correct way of doing things.

"Sword and Shield" theory

• Thomas Carlyle claimed – Combatants who held their sword in the right hand

and shield in their left (and therefore better protected their heart) were more likely to survive in battle.

– The greater mortality of the left-handers in battle, then, is proposed as the mechanism driving the higher prevalence of right-handedness today.

"Mother with Baby" Theory

Developmental theories

Bakan's "Birth Stress" Theory (1973)

• That minor brain insults early in development caused left-handedness.

• Only partly accepted.• There are just too many lefties for brain

damage to be the major culprit.

Geschwind and Galaburda's "Testosterone" theory(1987)

• Prenatal hormone exposure• Another study in 2003 determined that males

with in-utero exposure to Diethylstibestrol were more likely to be left-handed over the clinical control group.

Previc's "Vestibular-Monoaminergic" theory. (1991; 1996)

• The position of the foetus in the final trimester and a baby's subsequent birth position can affect handedness.

• This partly explains why prematurity results in a decrease in right-handedness.

• Previc argues that asymmetric prenatal positioning creates asymmetric stimulation of the vestibular system, which is involved in the development of handedness.

Evolutionary theories

MacNeilage's (1991) "Postural Origin"

• The first evolutionary step in hemispheric specialization was a left-hand, right-hemispheric visuospatial specialization for unimanual predation.

• Then it lead to a right-side, left-hemispheric specialization for postural support.

MacNeilage's (1991) "Postural Origin"

• Because the respiratory and phonatory components of language production are influenced by postural factors, and facial and whole-body communicative gestures played a principal role in early communication, the left hemisphere may have been predisposed for language functions (MacNeilage, 1991).

Division of labour(Corballis ;1991)

• Handedness and language -same hemisphere because they both require similar fine motor control.

Genetic theories

• Charles Darwin who, although right-handed himself, was puzzled by his left-handed son, noting that his brother, mother and grandfather were all also left-handed.

McManus and Mckeever studies.Parents of the Child McManus Study McKeever Study

Both Right Handed 9% 16%

One Right handed 19% 20%

Both Left handed 26% 40%

Right shift Theory

• Marian Annett back in 1972. A hypothetical RS+ gene (a “right shift”).

• According to this theory, then, left-handers do not inherit their hand preference per se, they merely inherit a lack of neurological bias towards a dominant left hemisphere.

Dextral/Chance Theory• Chris McManus hypothesized a “dextral” (D)

allele, which strongly biases handednes in favour of the right hand along with an alternative “chance” (C) allele, which is presumed directionally neutral.

• DD genotype • CC genotype • Heterozygotic DC genotype • What is being inherited is not left-handedness as

such, but rather an absence of handedness, so that handedness is then determined by chance.

• Annett’s RS+ and RS- genes and McManus’ D and C genes all remain hypothetical

• In 2007, Oxford University researchers LRRTM1 (Leucine-Rich Repeat Trans-Membrane 1), a variant of which also slightly increases the risk of psychotic mental illnesses.

• In 2010 , PCSK6 and handedness in children with language-related disorders like dyslexia.

HANDEDNESS, THINKING AND HEMISPHERIC DOMINANCE

Handedness and Thinking

• One theory divides left- and right-handed thinkers into two camps: Linear Sequential vs. Visual Simultaneous

• Ex.Popcorn

Handedness and Thinking

• Right-handed people process information using "analysis", which is the method of solving a problem by breaking it down to its pieces and analysing the pieces one at a time.

• Left-handed people process information using "synthesis", which is the method of solving a problem by looking at the whole and trying to use pattern-matching to solve the problem.

• Ultimately, being left handed is not an all or nothing situation. The processing styles operate on a continuum

Intelligence

• It’s a common belief that left-handed people are more intelligent or creative than right-handed people.

• While there is an unresolved debate within the scientific community on how to operationalize both intelligence and creativity, some studies have demonstrated a small positive correlation

• Marian Annett indicated significantly more left-handers among mathematics students than among students of other subjects, arguing that this is consistent with her genetic right shift theory of left-handedness.

• John Santrock's 2008 study, also suggested that more mathematicians, architects, musicians and artists - all of whom, it is argued, require good visual-spatial skills - are left-handed than the population as a whole.

FACT

• Contrary to earlier assumptions, only about 20% of left-handers have right-hemisphere language dominance.

• Thus, while left-handers may be largely right-brain dominant in terms of motor control, this may or may not be associated with any of the commonly-claimed right-brain attributes (such as intuition, creativity, imagination, etc).

MYTH• Studies in the late

1980s, showed left-handers tend to die early. In one study, (1991), they claimed that left-handers may die up to nine years earlier than right-handers.

FACT• Studies were seriously

flawed and conclusions erroneous.

• The findings were roundly refuted by more than a dozen studies in the 1990s.

MYTHS & FACTS

• FACT– Interactive sports such as table tennis, badminton,

cricket, and tennis have an overrepresentation of left-handedness, while non-interactive sports such as swimming show no overrepresentation.

MYTHS & FACTS

• The advantage to players in one-on-one sports, such as tennis, boxing, fencing or judo, is that, in a population containing perhaps 10% left-handers and 90% right-handers, the left-hander plays 90% of his or her games against right-handed opponents and is well-practiced at dealing with this asymmetry. Right-handers play 90% of their games against other right-handers. Thus, when confronted with left-handers, they are less practiced.

MYTH• Heterosexual individuals

are somewhat more likely to be right-handed than homosexual individuals.

FACT• Handedness and sexual

orientation may be linked to the faternal birth order and there s no definite increased incidence of homsexuality in left handers..

MYTH• Left-handers earn lower

wages than their right-handed counterparts

FACT• In a study published

in Laterality, it was found that lefties earn slightly more money than their right-handed peers who work at the same jobs.

FACT• An intresting report in Current Surgery says

“One out of every 10 left handed surgeons is uncomfortable with the idea of being operated on by a left handed surgeon”

• Six per cent also reported concerns by patients about their laterality .

FACT

• Left-handers might have the advantage in careers like piloting a jet fighter or talking and driving at the same time.

• A study published in the journal Neuropsychology in 2006 suggests that left-handed people are faster at processing multiple stimuli than righties.

MYTHS & FACTS

• The Romans were responsible for a lot of anti-left customs. They were the most militantly right-handed people in history. Romans invented the right handed handshake, the fascist salute, and that right to left alphabet that still creates a lot of trouble for lefties

Myths and Facts

• It was no coincidence that the fourth finger of the left-hand was chosen for the wedding finger in 300BC.

• Doctors at that time believed a nerve from this finger ran directly to the heart

MYTHS & FACTS

• Handshakes Whilst Julius Caesar was left-handed it was he who instructed all of his Roman subjects to adopt the right-handed handshake. Maybe this was because it left his weapon hand free whether greeting either friend or foe.

Left hand drive/Right hand drive

• When passing a stranger on the road, it would be safer to walk on the left, so ensuring that your weapon was between yourself and a possible opponent.

• Revolutionary France was to overturn this historic practice, as part of its social rethink.

• Also Napoleon was left handed. • From this time any part of the world that was

colonised by the French would travel on the right, the rest would remain travelling on the left.

Politics(Leftists)

• In the French parliament before the revolution, the nobles sat in the right side of the king, while the capitalists sat on the left.

• The right became associated with the prevalent social order, and the left with the subversive elements wanting to change it.

• It was founded by the Left-Handers Club in 1992, with the club itself having been founded in 1990.

Handedness Issues

Handedness Issues

• Historically, the left side, and subsequently left-handedness, was considered negative.

• The word "left" itself derives from the Anglo-Saxon word lyft, "weak“.

• Latin adjective sinister/sinistra/sinistrum originally meant "left“

• In Sanskrit, the word "वा�म" (waama) stands for both "left" and "wicked."

Handedness Issues

• Social stigmatization of left hand/side.• Cleanliness.• Especially in Islam and Hinduism• Christianity, the right hand of God is the

favoured hand. For example, Jesus sits at God's right side.

Forced use of right hand

• Can cause multiple problems - learning disorders, dyslexias, stuttering and other speech disorders

• Shifts from left- to right-handed are more likely to be successful than right to left, though neither have a high success rate to begin with.

Handedness Issues• Nearly all tools and devices are designed to be

comfortably used with the right hand.• For example, scissors.

Tools and devices

• Opening Bottles• Computer input devices; QWERTY keyboards• Cameras• Musical instruments • Weapons • Machinery

WRITING PROBLEMS

• Desks designs• Sitting arrangements

Awkward Social situations• Shaking hands with the non-dominant hand; • Accidentally taking a neighbour’s drink at

the dinner table; • Putting a belt on upside down; • Receiving Prasadam at a temple in an

unexpected hand.• Difficulty tying shoe laces• Opening Bottles• Trouble opening or locking locks/Screws.

• Narendra Modi*• Dr. Raman Singh• Ratan Tata• Laxmi nivas Mittal• Sachin Tendulkar• Ted Williams• Frankie Albert• Pt.Hariprasad Chaurasia• Mahatma Gandhi• Amitabh Bachchan• Saurav Ganguly• Alexander The Great• Charlie Chaplin• Bill Gates• Bill Clinton• J.K. Rowling• James Cameron• Gary Kasparov• Marie Curie

• Barack Obama• Henry Ford• Tom Cruise• Bruce Willis• Oprah Winfrey• Napoleon Bonaparte• Julius Caesar• Prince Charles• Leonardo Da Vinci• Angelina Jolie• Diego Maradona• Monica Seles• Martina Navratilova• Benjamin Franklin• Hellen Keller• John F. Kennedy• Rafael Nadal• Thomas Jefferson• Leo Tolstoy• Mark Twain

FAMOUS LEFT HANDERS

• Left Brain, Right Brain: Facts and Fantasies Michael C. Corballis mail Published: January 21, 2014DOI: 10.1371/journal.pbio.1001767

• Corballis MC (2009) The evolution of language. Ann N Y Acad Sci 1156: 19–43. doi: 10.1111/j.1749-6632.2009.04423.x

• McManus IC, Davison A, Armour JAL (2013) Multilocus genetic models of handedness closely resemble single-locus models in explaining family data and are compatible with genome-wide association studies. Ann N Y Acad Sci 1288: 48–58. doi: 10.1111/nyas.12102

• Corballis MC, Beale IL (1993) Orton revisited: dyslexia, laterality, and left-right confusion. In: Willows DM, Kruk RS, Corcos E, editors. Visual processes in reading and reading disabilities. Hillsdale (New Jersey): Lawrence Erlbaum Associates. pp. 57–73.

• McManus IC, Bryden MP (1992) The genetics of handedness, cerebral dominance and lateralization. In: Rapin I, Segalowitz SJ, editors. Handbook of neuropsychology, Vol. 6: developmental neuropsychology, Part 1. Amsterdam: Elsevier. pp. 115–144.

• http://www.rightleftrightwrong.com/• http://www.lefthandersday.com• http://en.wikipedia.org/wiki/Handedness• http://www.encyclopedia.com/topic/handedness.aspx

THANK YOU