| |
Abstract:
Abstract: Previous research with callosotomy ("split-brain")
patients has revealed a right-hemisphere superiority for spatial
judgements about visually presented stimuli. For right-handed
patients this finding presents something of a paradox, since the
left hemisphere outperforms the right in making fine-grained
visually guided (i.e., praxic) movements. We speculated that
right-hemisphere superiority would not be found for visuospatial
tasks that engaged the motor system to a greater degree. To
investigate this, we compared three conditions requiring a
split-brain patient to perform size discriminations on briefly
presented lateralized line segments. In one condition, the patient
performed a simple size-matching task that required a button press
to indicate which of two lines was longer. In the remaining two
conditions, the patient scaled the gap between his thumb and
forefinger to match the length of a line. The first of these
conditions simply required a size judgement. The second required
the patient to reach to the computer monitor and touch his thumb
and forefinger to the locations where the endpoints of the line had
been presented. The data revealed a marked right-hemisphere (left
visual field/left hand) superiority for both size matching and grip
scaling. This finding suggests that the right hemisphere advantage
for visuospatial processing is independent of whether the task
requires a perceptual or motor output. The paradox of left
hemisphere dominance for praxic movements remains
unresolved.
|
