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Abstract:
Although it is generally reported that mental rotation is a
right hemisphere function, more recent research suggests that there
may be different types of mental rotation that rely on different
neural substrates. The purpose of this study was to investigate
hemispheric differences in egocentric and allocentric mental
rotation. In both tasks, subjects were shown pictures of a man
holding a ball in either his right or left hand. The stimuli were
therefore the same in both conditions. The only difference between
the two mental rotation tasks was that one involved making a
decision with respect to an external frame of reference
(allocentric) and the other involved making a decision with respect
to an internal frame of reference (egocentric). In a split-brain
patient, it was found that the right hemisphere was superior to the
left in the allocentric mental rotation task. In the egocentric
task, however, this pattern was reversed, with the left hemisphere
performing significantly better than the right. This result was
followed up in neurologically normal subjects using functional MRI.
Using the same tasks, the same pattern of hemispheric function
emerged. Contrasting the allocentric with the egocentric task
revealed right hemisphere activation in the right superior parietal
region. A comparison of the egocentric to the allocentric task,
however, yielded left hemisphere activation.
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