PDA

View Full Version : An update on handedness and the preferred direction for turning(BIOMCH Archive 021282)



dmcfarlane
03-15-2006, 10:27 AM
It seems that handedness and chirality and direction of turning might
all be inter-related. Professor David Morgan (of Biomedical Engineering,
Monash University) told me that; "My understanding is that driving on
the left in Europe is due to Napoleon, on purely ideological grounds,
i.e. with liberty and fraternity ruling the land, having your sword
available is not needed. Similar to the scouts left handshake" (i.e. I
trust you to not draw your sword!)

Bruce Etnyre (Kinesiology Department, Rice University) has found the
BIOMCH-L archive reference for the responses to the first BIOMCH-L
discussion about turning left and right: it is reference number 17883
(he found it by doing a search for "left turn"). It was mainly about
counter-clockwise running tracks but also included some discussion about
how many things in general, naturally turn to the left or
counter-clockwise.

Chris Barr told me this interesting anecdote that might explain a few
things: "My mum was left handed as a child, and is now right handed
(although not quite of retirement age.) The reason she gives for this
is that at school writing with you left hand was "wrong". When she was
at school the teachers would actually tie her left hand behind her back
or give her the cane on her left hand in order to make her write with
her right hand. This type of incident was in no way isolated, and may
account for the change in stats."

On this topic Bruce Etnyre pointed out while the conventional assumption
is that 10% of people are left-handed and 90% are right-handed, he has
seen data that suggests that adolescents and pre-adolescents have about
20% left-handed, late teens to 20's is about 15%, middle age is about
10%, elderly is 5% and there are virtually no lefties over 80 y/o.

Conrad Pearson (of siliconCOACH Ltd) raised the question of whether
right handed people are always left footed. He provided the following
reference:
"Handedness and longevity: archival study of cricketers" by John P
Aggleton, J Martin Bland, Robert W Kentridge, Nicholas J Neave: this
study tested whether handedness is associated with a change in
longevity: their study looked at all first class cricketers born in the
British Isles between 1840 and 1960 whose bowling hand was specified
(right, n=5041; left, n=1132). A regression analysis of 5960 players
showed no significant relation between mortality and handedness. Left
handedness was, however, associated with an increased likelihood of
death from unnatural causes and this effect was especially related to
deaths during warfare.

Siegfried Jaecques (of K.U. Leuven, Belgium) mentioned that he
remembered reading about "a theory (maybe from a discussion on biomch-l)
that the statistics on survival of left-handers vs right-handers were
made with demographic data that spanned World War I and WWII. See
Aggleton (1994. Indeed the left-handers had a higher probability of
death in combat because weapon systems in those days were designed for
right-handers. For example, the action of a standard rifle is very hard
to operate with the left hand since the bolt handle is on the right. If
you saw the movie "Saving private Ryan", you may remember that the
sniper in the squad of Captain Miller is left-handed and there are a few
scenes where you can see that his left sleeve gets stuck on the scope
will cycling his gun. In the end, he gets shot by a German tank that he
spotted too late because he was distracted."

Bruce Etnyre made some similar remarks on this point: "Some explanations
why left-handers don't live as long, on average, is that there are about
50% more males than female left-handers. Males don't live as long, on
average. Why? It goes to the nature and nurture question. Males
participate in more risky behaviors than females, generally, so they get
killed more often. Probably the most dangerous activity of daily living
is driving a vehicle. Males, on average, drive more miles than females.
Also, because left-handers live in a world primarily designed for
right-handers, they are involved in more fatal accidents. For example,
here are some things designed for right-handers which can be dangerous
when used left-handed: firearms; gear shifts & gas/brake pedals (at
least in countries driving on the right-hand side of the road); all
power tools; and I'm sure there are others. Lefties are also frequently
frustrated with other objects made for righties: watch stems;
thermometers; musical instruments; cork screws, etc. etc. Also, infant
and peri-natal mortality is greater for males (although their handedness
has not been determined yet - generally that occurs at the developmental
milestone of about 4-6 years). More males dying dying before age 1
brings down the average considerably.

Noel Lythgo (Royal Talbot Rehabilitation Centre, Melbourne) has told me
that: "work involving small groups of no more than 20 able-bodied young
and elderly adults (Sadeghi, Allard & Duhaime, 1997; Sadeghi, 2003;
Sadeghi et al., 2003; Goble, Marino & Potvin, 2003, Sadeghi et al.,
2004) suggests the behaviour of the limbs is symmetrical for outcome
measures such as step length but asymmetrical for the lower limb moments
that produce the step. This supports the idea of functional gait
asymmetry, where one limb has a propulsive function and the other a
supporting or stabilising function. This may lead to the tendency to
circle when lost. Essentially, longer left steps are made due to the
greater propulsion or push-off generated by the right limb (which
carries the left limb further through the swing phase) coupled with
shorter right steps made due to the lesser propulsion generated by the
left limb (assuming right limb dominant)."

Last but not least: according to a recent theory ("Hemispheric Asymmetry
Reduction in Old Adults" or HAROLD) bi-hemispheric load-sharing might
compensate for some aspects of age-related neuro-cognitive decline. You
might have seen the recent article in "Time" magazine about "The
Surprising Power of the Aging Brain": perhaps this "brain balancing"
might also account for the ability of some "left-handers" to eventually
learn to do tasks with their right hands (or become ambidextrous). Here
is a little background information for anyone who is interested in doing
further research on this topic. Positron emission tomography (PET) and
functional magnetic resonance imaging (fMRI) can reveal how brain
activity during cognitive performance changes as a function of aging
(Cabeza, 2001). Studies using these techniques have led to the
development of the new discipline of Cognitive Neuroscience of Aging.
This article reviews functional neuro-imaging studies of cognitive aging
in the domains of visual perception and memory functions. These studies
have shown that brain activity tends to be less lateralized in older
adults than in younger adults: this has led to a model of aging called
Hemispheric Asymmetry Reduction in Old Adults (HAROLD). According to
this theory bi-hemispheric load-sharing might compensate for some
aspects of age-related neuro-cognitive decline. The HAROLD model
integrates ideas and findings from psychology and neuroscience of aging
(Cabeza, 2002). Indeed some older adults perform as well as young
adults: recent studies of these high-performing older adults have shown
that the high-performing seniors counteracted age-related neural decline
through a reorganization of neuro-cognitive networks (Cabeza et al,
2002). This might have something to do with the finding that many senior
citizens achieve an increased balancing of the two halves of the upper
brain as they age. Dolcos et al (2002) have reviewed the evidence for
two models of aging and its relationship to hemispheric asymmetry: (a)
the right hemi-aging model (a model that proposes that the right
hemisphere shows greater age-related decline than the left
hemisphere) and (b) the theory hemispheric asymmetry reduction in old
adults (the "HAROLD model"): this model proposes that frontal activity
during cognitive performance tends to be less lateralized in older than
in younger adults. The authors concluded age-related asymmetry
reductions might reflect functional compensation ("de-differentiation")
and found that there is some slight evidence to support the compensation
hypothesis.

Regards,

David McFarlane
Ergonomist, WorkCover Authority
New South Wales, Australia

References

R. Cabeza, (2001), "Cognitive neuroscience of aging: contributions of
functional neuroimaging", Scand J Psychol, Jul; 42(3): 277-86.

R. Cabeza, (2002), "Hemispheric asymmetry reduction in older adults: the
HAROLD model",
Psychol Aging, Mar; 17(1): 85-100.

R. Cabeza, N. Anderson, J. Locantore and A. McIntosh, (2002),
Neuroimage, "Aging gracefully: compensatory brain activity in
high-performing older adults",
Nov; 17(3): 1394-402.

F Dolcos, H. Rice and R. Cabeza, (2002), "Hemispheric asymmetry and
aging: right hemisphere decline or asymmetry reduction", Neurosci
Biobehav Rev. Nov; 26(7):819-25.

J. Kluger, (2006), "The Surprising Power of the Aging Brain", Time,
January 16, 84-87.

Disclaimer
Any recommendation concerning the use or representation of a particular
brand of product in this document or any mention of them whatsoever
(whether this appears in the text, illustrations, photographs or in any
other form) is not to be taken to imply that WorkCover NSW approves or
endorses the product or the brand.


************************************************** ************************************************** ************************************

This message, including any attached files, is intended solely for the addressee named and may contain confidential
information. If you are not the intended recipient, please delete it and notify the sender. Any views expressed in this
message are those of the individual sender and are not necessarily the views of WorkCover NSW.

************************************************** ************************************************** ************************************