by using one hand or the other to indicate an answer.
Suppose that a picture of an object was flashed to the
right visual field. Since in most people verbal ability
is restricted to the left hemisphere, the patient could
then say exactly what it was. But if it was flashed to
the left side, he could not. In other words, the left
hemisphere, with its ability to control speech, ‘knew’
the correct answer only when the picture appeared
on the right. In anyone with an intact corpus callo-
sum the information would quickly flow across to
the other side of the brain, but in these split-brain
patients it could not. The interesting finding was that
the right hemisphere could communicate in other
ways. So if a pile of objects was given, out of sight,
to the left hand, that hand could easily retrieve the
object seen in the left visual field.
Tasks could even be done simultaneously. For exam-
ple, asked to say what he had seen, a patient might
reply ‘bottle’, while his left hand was busy retrieving
a hammer from a heap of objects – or even retriev-
ing a nail as the closest association. When a dollar
sign was flashed to the left and a question mark
to the right, the patient drew the dollar sign, but
when asked what he had drawn he replied ‘a ques-
tion mark’. As Sperry (1968) put it, one hemisphere
does not know what the other is doing; each can
remember what it has seen but these memories are
inaccessible to the other. This means the left hand
could retrieve the same object an hour later, but the
person speaking through the verbal left hemisphere
would deny ever having seen it.
Sperry thought that these results revealed a dou-
bling of conscious awareness, and even that his
patients had two free wills in one cranial vault.
‘Each hemisphere seemed to have its own separate
and private sensations’, he said, and he concluded
that ‘the minor hemisphere constitutes a second
conscious entity that is characteristically human
and runs along in parallel with the more dominant
stream of consciousness in the major hemisphere’
(1968, p. 723). In other words, for Sperry a split-brain
patient is essentially two conscious people.
Koch agrees, claiming that ‘split-brain patients har-
bor two conscious minds in their two brain halves’,
and asking ‘How does it feel to be the mute hemi-
sphere, permanently encased in one skull in the
company of a dominant sibling that does all the
talking?’ (2004, pp. 294, 293).
ACtIVItY 6.1
Are you a synaesthete?If you have a large class or other group of people that
you can easily test, you can ask people whether they
ever experience one sense in response to another, or
whether they used to do so as a child. Some people
can describe vivid memories of seeing coloured music,
or experiencing tastes and smells as having a particular
shape, even though they can no longer do so. You may
find people who claim extravagant associations and
florid experiences. Here are two simple tests that might
help detect whether they are making it up or not.
1 Retesting associations. This test needs to be
done over two separate sessions, without telling
participants that they will be retested. In the first
session read out, slowly, a list of numbers in random
order (e.g. 9, 5, 7, 2, 8, 1, 0, 3, 4, 6) and a list
of letters (e.g. T, H, D, U, C, P, W, A, G, L). Ask your
group to visualise each letter or number and write
down what colour they associate with it. Some will
immediately know, while others may say they are
just making up arbitrary associations. Either way
they must write down a colour. Collect their answers
and keep them. In a second session (say a week or
several weeks later), read out the same letters and
numbers but in a different order (e.g. 6, 3, 8, 1,
0, 9, 2, 4, 5, 7; P, C, A, L, T, W, U, H, D, G). Give
them back their previous answers and ask them to
check (or to check a neighbour’s) and count how
many answers are the same. True synaesthetes
will answer almost identically every time they are
tested.
2 Pop-out shapes. Tell the group that you will show
them a pattern in which a simple shape is hidden.
When they see the shape they are to shout out
‘Now’. Emphasise that they must NOT say the name
of the shape and give the game away, but must
just shout ‘Now’. As soon as you show the pattern
(Figure 6.7), start timing as many of the shouts as
you conveniently can. If you have any synaesthetes in
the group, they will see the pattern much sooner than
everyone else. Even if you have no synaesthetes,
these figures can help everyone else to imagine what
synaesthesia is like.