FoundationalConceptsNeuroscience

brain circuitry controlling the left hand. The objects being felt are hid-
den from view behind a screen, for if the person were to look at them
while choosing, both hemispheres would have access to the identities
of the objects.
Another variant of this experiment has the subject looking at a
visual display in which two different pictures are flashed, one to the
right visual field and another different one to the left visual field. For
example, a picture of a spoon might be flashed to the right visual field,
and a picture of a pencil flashed to the left visual field. The split-brain
patient is then instructed to select the object she saw from among sev-
eral objects she can feel with her hands behind a screen.
As expected, she will select a spoon with her right hand anda
pencil with her left hand. However, when asked to say what she saw,
she will say only that she saw a spoon. She cannot say that she saw a
pencil, because that information (from the left visual field) only went
to the nonspeaking right hemisphere. At this point, you instruct the
person to remove her hands, together with the objects she selected,
from behind the screen. Now the left hemisphere sees and becomes
aware of the pencil. You ask why she chose a pencil with her left hand,
because she was only supposed to choose the object she had seen on
the screen. The patient might say “I don’t know.” However, sometimes
the patient will make up a story, perhaps something like, “Well, I
picked up the pencil so that I could write down a list of the things I
wanted to eat with the spoon.”
That’s really interesting! There have been many variations of
experiments like this where split-brain subjects are presented with
conflicting information to their two cerebral hemispheres. It is clear
that the right hemisphere is quite capable of decisions, judgments,
and so forth, but just can’t speak about what it is up to. In such
circumstances, the verbal left hemisphere may make up a story to ex-