Evaluation of Biological Area – Sperry – Regions of The Brain
Abilities of the RIGHT Hemisphere
- Before Sperry conducted his research not much was known about the right ‘silent’ hemisphere
could do.
- Tests with the split-brain patients showed a range of higher-order mental abilities, including
some verbal comprehension.
- There are some abilities that even appear to be dominant in the right hemisphere, such as
spatial awareness and emotion.
Closing Statements
- Patients appear to have two independent streams of consciousness, each with its own
memories, perceptions, impulses to act; in a sense TWO MINDS IN ONE BODY.
- Sperry ends the article by saying: ‘ The more we see of these patients and the more of these
patients we see, the more we become impressed by their individual difference’.
- These differences might explain the contrasting results collected by different investigators. For
example: some patients display some ipsilateral control (right hemisphere can communicate
with right hand, i.e. same side of the body)
- Such patients wouldn’t display some of the behavioural effects.
Things the RIGHT hemisphere could do in split-brain patients:
HUMAN MENTAL CAPACITIES – if patient holding an object in LEFT hand they van point to the name of
the object displayed in their LVF. This shows that the RIGHT brain has some distinctly human mental
capacities since a monkey couldn’t perform these tasks.
UNDERSTANDING OF GENERAL CATEGORIES – patients an select objects related to a picture item
presented to LVF, task requires mental processing. For example: if picture of clock on wall shown to
RIGHT hemisphere (LVF), LEFT hand will select a toy wristwatch. This shows that the RIGHT hemisphere
has grasped the general category (timepiece) and not just search for a physical match.
SIMPLE ARITHMETIC PROBLEMS – For example: if number shown to the LVF, the left hand (held out of
sight) can signal the correct answer. If 2 different pairs of numbers were shown to RVF and LVF
separately, the right and left hands can signal 2 separate answers but the patient will only say the
answer to the RVF.
RESPONDING TO SPOKEN CLUES – if an object is named out loud, the LEFT hand (RIGHT hemisphere) can
locate the object because hearing is partially BILATERAL – about 10% goes to the same side and 90%
foes to the opposite hemisphere.
SORTING – the LEFT hand can sort objects into groups by touch on the basis of shape, size and texture.
SPATIAL AWARENESS – on some tests the RIGHT hemisphere was found to be superior to the LEFT
(major) hemisphere – on tests that involve drawing spatial relationships and performing block design
tests.
EMOTION – if a pin-up picture is shown in a series of geometric figures to the LVF there is an emotional
reaction (e.g. giggling) but the patient usually says he saw nothing or just a flash or light. The patient
who saw the picture with his LVF can’t be explained why he giggled.
Sperry showed that the LEFT and RIGHT hemispheres display functional laterization.
In other words each side has different functions.
For example, the LEFT side (hemisphere) is the MAIN LANGUAGE CENTRE and the RIGHT side has
CENTRES FOR SPATIAL AWARENESS AND EMOTION.
In split-brain patients the signal from the LVF of the LEFT eye will not pass through to the RIGHT
hemisphere, and the same is true for the RVF and the RIGHT eye.
Positives and Negatives of the Sperry Split-brain Study / Evaluation
. Clearly demonstrated laterization of function (POSITIVE)
- Split-brain research was pivotal in establishing the differences in functions between the two
hemispheres.
- The LEFT hemisphere was demonstrated as being DOMINANT FOR LANGUAGE TASKS. This is due
to CONTAINING LANGUAGE CENTRES, whereas the RIGHT hemisphere was demonstrated as
being DOMINANT FOR VISUO-SPATIAL TASKS.
- Therefore, this suggests that the LEFT hemisphere is THE ANALYSER, whereas the RIGHT
hemisphere is THE SYNTHESISER.
- So there are marked differences between the two.
. Contribution to discussions about laterization theories (POSITIVE)
- Such evidence strongly supported the idea of a ‘DUAL MIND’ where the two hemispheres
represent two sides of the mind.
- Pucetti (1980) critisised Sperry and Gazanigga’s work by pointing out that “visual stimuli
impinging on the LEFT half of the retina is concave and each half retina receives light from the
contralateral side of the body”
- Therefore, it is clear that split-brain research has sparked much debate about the psychological
and theoretical basis of brain function and human abilities.
. Lack of control with the sample selection
- The epileptic patients has been taking anti-epilepsy meds for extended and different periods of
time, which may have affected their ability to recognize objects and match words.
- This is due to causing cerebral neuronal changes.
- Secondly, although all patients had undergone a commissurotomy, there may have been
differences in the exact procedures.
- For example, differing extent of the lesioning of the corpus callosum.
- This would have affected the degree to which the two hemisphere could relay information
between themselves.
- Therefore, these two confounding variables had not been controlled, meaning that the
lateralized functions may be examples of unreliable casual conclusions.
. The differences in function may not be so clear-out
- With evidence making the drastic distinctions that the left hemisphere is responsible for
language (analyser) whilst the right is responsible for visual-spatial tasks (synthesizer), this has
given the public the false impression that the two hemispheres are ‘opposite’ in function and
that they can receive such labels.
- However, as suggested by Pucetti (1980), there have been cases of split-brain patients where
left-handed but produce and comprehend speech in the RIGTH hemisphere.
- This opposes the predictions made by laterization theory.
- Therefore, it is important not to jump to conclusions and to appreciate that, through
recruitment of homologous areas on the opposite side of the brain.
- Each hemisphere is not restricted to specific functions.