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Abstract:
The coordination of the left and right hands involves
interhemispheric communication via the anterior callosum, which may
be larger in left-handers, compared to consistent right-handers. In
the present study 13 left-handed (LH) subjects were compared to 15
right-handed (RH) subjects on a test of bimanual coordination
(Brown, 1991). Subjects were required to draw lines at various
angles on an Etch-a-Sketch by simultaneously manipulating two
knobs, one on the left, which moved the cursor horizontally, and
another on the right that moved it vertically. The angle at which
the line was to be drawn was indicated by parallel guide lines. LH
subjects made more errors (went outside the guidelines) than RH
subjects at all angles. For time, there was a handedness by angle
interaction. LH subjects were slower when the right hand had to
turn faster than the left, but RH subjects were slower when the
left hand had to turn faster than the right. In addition, LH
subjects were significantly slower when both hands had to turn
counter-clockwise than when one hand turned in each direction. This
condition requires the use of non-homologous muscles by the two
hands. The results suggest that the larger anterior callosum found
in LH subjects in some studies may not reflect superior
interhemispheric integration. Instead, it may reflect the
additional processing load required in some LH subjects when motor
programming does not take place in the hemisphere controlling the
movement.
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