Notes on R. W. Sperry's 1968 paper
Hemisphere deconnection and unity in conscious awareness
R.W. Sperry
The first thing to be sure about is that Sperry did not obtain subjects and then mercilessly cut their brains into two. The subjects were patients that had suffered uncontrollable epileptic seizures. Uncontrolled by medicine, that is; but their epilepsy had been contained by a surgical procedure that involved cutting the corpus collosum. The corpus collosum connects the two halves of the brain. Each half is called a hemi-sphere. The purpose of the surgery was to reduce the spread of electrical activity and therefore reduce the severity of epileptic fits or eradicate them completely. The surgery involved surgical deconnection. This is the division of the entire corpus callosum, which contains nerve fibres joining the 2 hemispheres. These fibres would normally allow the 2 sides of the brain to communicate, but when these fibres are cut such communication is no longer possible and the right hand side of the brain is unaware of what the left-hand side is doing!
The ethical reason for cutting the brain into two is that the subjects stand a high chance of dying if the operation is not performed. Oddly enough, this drastic surgical procedure leaves the subject's personality or cognitive processing capacity relatively unchanged. Patients do, however, experience short-term memory deficits, have orientation problems and find tasks, such as reading, quite tiring.
The subjects. Sperry describes 11 people who had undergone this
surgery. 9 had only had the surgery recently before the paper was published.
The other 2 had had the surgery a while ago. He reported excellent recovery.
Neither of these 2 had experienced a fit since surgery. The surgery had few
side effects. The patient’s ability to function in everyday life was barely
affected. There were some problems with short-term memory and concentration
span, but no changes in intelligence and personality. The peculiar results of
Sperry’s laboratory studies of these people do not occur outside of the
laboratory in normal conditions.
Method of research and other methodological details. The study can be described as a quasi-experiment (or a naturalistic experiment) The IV is the presence or absence of brain surgery. The DV is the subject’s performance on a variety of tests. However, as each of these people are described in detail it could also be argued that Sperry’s work is a series of case studies.
The research question really is to find out what cognitive functions take place in each hemisphere. As the two halves are separate in Sperry's patients this provides a rare chance to isolate the functions within each hemisphere. Using 'normal' subjects would be of no use because what ever gets processed in one hemisphere gets quickly passed to the other hemisphere through the corpus collosum. Sperry's patients have been able to overcome this problem of one half of the brain not knowing what the other is doing by shifting their gaze. By doing this information received on the right of the visual field (processed by the left hemisphere), is also received on the left of the visual field by the patient shifting their gaze to their right. These compensatory tactics would be carried out unconsciously; The patient would not be aware of their two halves not communicating. Another tactic would be to speak aloud information that had been processed by the main language area of the brain (usually in the left hemisphere). This information could be 'heard' by the right hemisphere, which has limited language processing ability.
In order to test the patients, Sperry has to make sure that information is processed by just one hemisphere. He does this by asking the patient to fix their eyes on a particular spot (the fixation point), and then two words or pictures are projected either side of this point for 1/10th of a second. This prevents the subject from having time to shift their gaze. The problem of finding out what each hemisphere has 'seen' is resolved by asking the patient to feel for a particular object, hidden amongst others out of sight behind a screen.
If the words 'KEY' and 'CASE' are projected either side of the fixation point a normal person would be able to say that they have seen 'KEY CASE', but the commissurotomized patients report having seen only the word 'CASE'. As the word 'CASE' is seen on the right of the visual field, then it is reasonable to assume, for that patient at least, that the right visual field and language are processed within the same hemisphere (the left). To find out whether the patient's right hemisphere saw the word 'KEY', Sperry would ask him or her to search amongst the hidden objects using one hand. If the left hand was used the patient was usually successful in picking out the corresponding object (a key in this example); However, if the right hand was used the patient's ability to pick the correct object was at chance level.
The
main findings are that the left visual field is processed by the right
hemisphere and the left hand is controlled by (and tactile information from the
left hand is received by) the right hemisphere; and vice versa.
If an object is placed in the right hand, without the patient seeing it, she is able to name the object. If the object is placed in the left hand then the patient is unable to name the object, but is able to retrieve it from amongst several objects placed in a grab bag, provided the same (left) hand is used.
The patient is unable to express verbally the sensations of the left hand and would be likely to claim that they cannot work with the hand or that it feels numb. Success with the left hand is explained as guesswork.
The hemisphere that processes language (usually the left) is known as the major hemisphere. The other hemisphere is known as the minor hemisphere. Sperry was able to demonstrate limited language processing ability in the minor (right) hemisphere. In one experiment a picture of a wall clock would be shown to the minor hemisphere, and the patient was able to pick out a wristwatch with the left hand (which is controlled by the right hemisphere). As a wristwatch is physically nothing like a wall clock, it can be assumed that the patient was not guided by a visual image alone. It is reasonable to assume that semantic processing took place, as the link between the two objects (being their similarity of function) is purely semantic. In another experiment, when the subject was asked to pick out a 'piece of silverware', for example, their left hand could successfully retrieve a fork.
Sperry was also able to demonstrate that the right hemisphere can perform simple arithmetical calculations. This is normally more efficiently performed within the left hemisphere. Simple sums would be presented to the left visual field, and therefore processed by the right hemisphere. The left hand was able to indicate the answer by pointing to or writing the correct answer.
The minor (right) hemisphere can express emotion. A pin-up of a nude presented in the left visual field (and hence processed by the right hemisphere) would produce blushing or giggling, but no verbal report of having seen the picture. An unpleasant smell presented to the right hemisphere (through the right nostril) would produce the response 'phew' but no verbal report of what the smell was like.
The functions of the right hemisphere
(minor hemisphere)
The right hemisphere seems to be able to do the following.
Read words. Although the person cannot say what a word is when it is
presented to the right hemisphere (it cannot speak) it is clearly able to read
the word as the object can be picked out by the left hand. Being able to see
a word and then recognise the object through touch is referred to as cross-modal
transfer.
Make mental associations e.g. if shown a picture of a watch the person is able to select a clock from a series of items.
Emotional reactions. When one female subject was flashed a picture of a nude to the right hemisphere she laughed and blushed, yet was unable to say why she was laughing.
Solve simple math’s problems and write down the answers with the left hand.
The right hemisphere is better than the left at problems involving spatial skill.
Exercises
Subjects are shown this.
KEY
CASE
- If asked to draw what they see using the left hand, what will they draw and why?
- If asked what they have just drawn what will they say and why?
- An object is put into the right hand for identification. Can they say what it is?
- An object is put into the left hand. The person cannot say what it is and may even deny that there is anything there! If the same object is taken from their left hand and put into a bag with several other objects the left hand can pick the object out. Explain this.
- Would the person have been equally successful if the right hand had been put into the bag rather than the left? Explain your answer.
The absence of a corpus collossum from birth.
"Although people born without a corpus callossum do not show the usual effects of split-brain surgery, they are nevertheless far from normal. For example, although they can co-ordinate the movements of their two hands to lace and tie their shoes, they do so very slowly (Sauerwein, Lassonde, Cardu & Geoffroy, 1981). Their language abilities in general are impaired, even on tasks that have nothing to do with the left versus right side of the body. The exact language impairment varies from one person to another, but may include difficulty of thinking of words that rhyme with a particular word (Temple, Jeeves, Vilarroya, 1989) or understanding passive sentences (Jeeves & Temple, 1987; Sanders, 1989). Evidently the "cost" of reorganising the brain is that the left hemisphere does not develop its full, normal language capacities."
Kalat, J. W. (1992). Biological Psychology. (4th ed.). Pacific Grove, CA: Brooks/Cole.
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THE TWO SIDES OF FACE PROCESSING (An idea for your experiment)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Each hemisphere of the brain mostly processes the opposite side of space. That
means
if one hemisphere were more dominant for processing human faces, we would have
a
stronger representation of the side of people's faces opposite that hemisphere.
Nuala
Brady and colleagues at University College, Dublin investigated.
They combined one half of a facial photograph with a mirror-reversed copy of
itself
to create either a left-left or right-right facial 'composite'. At first glance
it
looks like a normal face, but it's actually made up of two copies of one side
of the
same face stuck together.
Brady and her team showed 99 participants left-left composites and right-right
composites of their friends' faces. The participants had to say which
photographic
composite - the left or right - most resembled the real-life appearance of each
friend. There was a significant tendency for them to choose the left-left
composites - that is, the composites made up of two copies of the left side of
the
friends' faces.
However, when the experiment was repeated with photos of people's own faces as
they
appear in the mirror, they showed the opposite bias. That is, participants
tended to
say the right-right composite of their own face (as they see it in a mirror)
resembled themselves more than the left-left composite.
"Our data suggest a dissociation in the recognition of self and
other...that opposite
hemispheres of the brain dominate in these two tasks", the authors said.
_____________________________________
Brady, N., Campbell, M. & Flaherty, M. (2004). My left brain and me: a
dissociation
in the perception of self and others. Neuropsychologia, 42, 1156-1161.
Journal weblink: http://www.sciencedirect.com/science/journal/00283932
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