handedness

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handedness,

habitual or more skillful use of one hand as opposed to the other. Approximately 90% of humans are thought to be right-handed. It was traditionally argued that there is a slight tendency toward asymmetrical physiological development favoring the right side of the body, and that the center of gravity is to the right of the body's midline. This, however, would seem to be the consequence of greater dependence upon the right hand rather than the cause of right-handedness.

The neurological argument holds that since the right and left sides of the body are controlled by the opposite hemispheres of the brain, the greater development of the left hemisphere results in right-handedness. Anatomical studies have demonstrated that Broca's center, the area of the cerebral cortex that controls speech and muscular coordination, is almost always better developed in the left hemisphere in right-handed individuals; in 70% of left-handed individuals these centers are located in the right brain. Psychologists have raised the possibility of a cultural explanation. Although young children can be trained to prefer the right hand against a natural inclination, there is evidence that handedness is hereditary and that denser neurological connections extending from one side of the brain or the other are present from birth. A cultural explanation is also challenged by the evidence that some other vertebrates demonstrate a preference for one hand or paw over the other.

Although it is not clear that culture is a causative agent in handedness, it is certain that the high incidence of right-handedness has shaped human society in almost every conceivable aspect. Tools, machinery, and even clothing are largely designed for the right-handed, and until fairly recently, many left-handed individuals were strongly encouraged to switch to right-handedness. In some cultures the left-handed were thought to be evil or to bring bad luck.

handedness

[′han·dəd·nəs]
(physics)
A division of objects, such as coordinate systems, screws, and circularly polarized light beams, into two classes (right and left), which distinguishes an object from a mirror image but not from a rotated object.
References in periodicals archive ?
Others did not show a clear hand preference as infants, but were either right or left-handed by age two.
Thus, even when compliance with the experimenter's request entailed no loss of reinforcement but only the possible inconvenience of reaching to the side opposite the hand preference, instructional control was weaker than it was when the request was expressed as a procedural requirement and compliance resulted in a loss of reinforcement.
A second limitation concerns the manner in which hand preference was assessed.
For instance, environmental models have difficulty explaining the similarities of children's early hand preferences to those of their parents, or similar parent-child hand preferences when children were raised apart from their biological parents (Bishop, 1990).
When subjects arrived for the session, their hand preference was ascertained by asking whether they preferred to "pick up things" with the right or left hand.
Each subject's gender and stated hand preference are also indicated.
The study, while limited in size, found no correlations betweens the side of facial involvement and hand preference that would support the theory of vascular disruption.
While moving fish attract the left hand, the monkeys show no overall hand preference in reaching for a stationary piece of food, the researchers say.
Many researchers suspect that specific genes contribute to human hand preferences.
Childhood tool use blossoms with the emergence of stable hand preferences and an upright posture, says Daniela Corbetta of Purdue University in West Lafayette, Ind.
In a variety of daily behaviors, such as grooming others and plucking fruit from trees, no hand preferences emerged in a group of 38 Gombe chimps observed last year for 3 months, Marchant and McGrew contend.