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Module 1.4c
Figure 1.4-21
One skull, two minds
When an experimenter flashes
HE•ART across the visual field,
a woman with a split brain
verbally reports seeing the
word transmitted to her left
hemisphere. However, if asked
to indicate with her left hand
what she saw, she points to the
word transmitted to her right
hemisphere (Gazzaniga, 1983).
“Look at the dot.” Two words separated by a dot
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
are momentarily projected.
(a) (b)
Copyright © Bedford, Freeman & Worth Publishers.
“What word did you see?” or “Point with your left hand
to the word you saw.”
(c)
their left hand to what they had seen, they were startled when their hand (controlled by the
right hemisphere) pointed to HE. Given an opportunity to express itself, each hemisphere
indicated what it had seen. The right hemisphere (controlling the left hand) intuitively knew
what it could not verbally report.
When a picture of a spoon was flashed to their right hemisphere, the patients could
not say what they had viewed. But when asked to identify what they had viewed by feeling
an assortment of hidden objects with their left hand, they readily selected the spoon. If the
experimenter said, “Correct!” the patient might reply, “What? Correct? How could I possi-
bly pick out the correct object when I don’t know what I saw?” It is, of course, the left hemi-
sphere doing the talking here, bewildered by what the nonverbal right hemisphere knows.
A few people who have undergone split-brain surgery have been for a time bothered by
the unruly independence of their left hand. It was as if the left hand truly didn’t know what
the right hand was doing. The left hand might unbutton a shirt while the right hand buttoned
it, or put grocery store items back on the shelf after the right hand put them in the cart. It was
as if each hemisphere was think-
ing, “I’ve half a mind to wear my Figure 1.4-22
green (blue) shirt today.” Indeed, Try this!
said Sperry (1964), split-brain sur- People who have had split-brain
gery leaves people “with two sep- surgery can simultaneously draw
arate minds.” With a split brain, two different shapes.
both hemispheres can compre-
hend and follow an instruction to
copy — simultaneously — different
figures with the left and right
hands (Franz et al., 2000; see also
Figure 1.4-22). Today’s researchers
The Brain: Damage Response and Brain Hemispheres Module 1.4c 83
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