The human body, like all mammalian bodies, exhibits bilateral symmetry with one
side of the human brain taking on primary functions of many of the body's muscle
systems. Each person has a dominant eye (something that can be easily determined
for each and every person). Approximately 70% of the population is Right Eye
Dominant (RED) and 30% Left Eye Dominant (LED). (This 70/30 percentage figure
holds true for other mammals as well). Lesser percentages abound in the
literature but no wide-based study has been done among a population where
cultural influences have not already skewed the testing subjects and the
question asked of the test subjects is not which is your dominant eye but "Are
you left or right-handed?"
There is a good, but not perfect, correlation
between Eye Dominance and right or lefthandedness. Cultural issues, such as
superstitions about the left hand being the 'hand of the devil,' have caused
many parents and teachers of left handed children to punish them for using their
left hands. Until recently, military rifles were designed to be shot from the
right shoulder only and left handed shooters suffered injuries from spent
cartridge casings hitting them in the eye and head!
The correlation between eye dominance and left or right-handedness exists
because of certain functions the dominant eye performs unconsciously for the
human body. In particular, the human brain relies on both the dominant eye, and
dominant side inner ear, to make subtle corrections in balance as a person sits
upright, stands and walks. The fluid levels in the inner ear stimulate membranes
that tell the brain when the head changes position and the dominant eye is used
to look at the horizon in order to correct the balance of the upright body as it
moves. This process occurs even as the body moves, by walking or running, and
can be observed, with some acrobatic difficulty, by a person walking in front
and to the side of another person and concentrating on the position of the pupil
of the eye in relation to the entire eye. As the subject walks, you will observe
slight up and down movement of the pupil as the eye maintains focus on the
horizon in front of the walker. This movement of the eye is not noticeable by
the subject and is not, therefore, something capable of "self-discovery."
Because humans walk on two legs, the gait pattern is, of necessity,
alternating -- hopping and skipping notwithstanding. In regulating balance, the
dominant eye also makes slight adjustments in the line of march or travel as the
person walks and those adjustments occur, unconsciously, as you transfer your
weight from your non-dominant foot to the dominant foot. The result of this
subtle correction is that humans take a slightly longer step with their dominant
foot and their toes of their dominant foot point more closely to the line of
march than do those of the nondominant foot. The angle of the foot from the line
of march is the "pitch angle" and the pitch angle of the dominant foot is
smaller in degree than that of the non-dominant foot, assuming a person without
deformity is walking upright without carrying anything. You can therefore
determine dominance by examining the tracks of a person and measuring either the
pitch angles or the stride lengths of the respective feet.
The body reflects this uneven use of the legs by making the calf muscles of
the dominant leg larger than those of the non-dominant leg. The dominant calf
muscles are larger because of the additional stretching they are called upon to
do in taking that longer step and the additional 'lifting' the calf muscle does
as the body's weight is transferred to the dominant leg. Also, the thigh muscles
of the non-dominant leg will be larger than those of the dominant side leg
because those muscles are used to 'push' the body forward in taking the longer
step with the dominant side leg. Because the dominant side hand is used for many
fine motor coordination skills, the muscles of the forearm will be larger than
those of the nondominant arm. And finally, because you take a longer step with
your dominant foot, the dominant side shoulder 'dips' lower than the
non-dominant shoulder does and this can be readily seen by walking behind a
subject on a flat surface and watching his/her shoulders.
This kind of information is obviously of use to athletes who must spend many
hours in weight training attempting to make the muscles on their non-dominant
side as strong as those on their dominant side. It should also be noted by
gerontologists who are faced with diseases of the joints which appear after a
'life time' of using joints unevenly.
Race tracks for horses favour right-side dominant horses which take a longer
stride with their right forelegs. That helps them turn to the left as they race
around the track. Trainers who are running Left Eye Dominant horses often put
blinders on the left eye to retrain the horse to look with his right eye and,
therefore, to turn the head slightly to the left to see forward and to take a
slightly longer step with the right foreleg just as RED horses do! You do not
find many racetracks where the horses run clockwise.
Eye dominance and the effect it has on the body is used by trackers and
police officers to locate missing children or adults and to help identify
criminal suspects from footprints found at crime scenes. When the number of
people who could be responsible for committing a crime is limited, dominance may
be the only evidence needed to solve a crime!
This article was
originally published in the Anthropology Information File (The Rocky
Mountain Institute of Anthropology, Red Deer, Alberta Canada).
Used with permission of the author.