Lateralisation And Split Brain Research Flashcards
What is hemispheric lateralisation?
Refers to the fact that some mental processes in the brain are mainly specialised to either the left or right hemisphere
Which sides of the body does each hemisphere control?
Left hemisphere= right side of the body
Right hemisphere= left side of the body
What is the corpus callosum?
A bundle of nerve fibres which join the two hemispheres of the brain
What is split-brain research?
Research that studies individuals who have been subjected to the surgical separation of the two hemispheres of the brain as a result of severing the corpus callosum
Name a split-brain study
Sperry and Gazzaniga (1967)
Describe briefly Sperry and Gazzinga’s study
Patient had an image projected to either their right or left visual field for 1/10th of a second. They were then asked to describe what they saw, do a tactile test or a drawing test
An object is placed in the left hand and the patient is asked to name it- predict what would happen and explain why
The patient will not be able to name it because object will be processed by right hemisphere, but language is in left hemisphere.
An object is placed in the left hand and the patient is asked to find the object with the right hand- predict what will happen and explain why
They will not be able to find the object because the object will be processed by the right hemisphere, which controls the left hand, not the right.
A word is presented to the right visual field and the patient is asked to name it.
They will be able to because right visual field is processed by the left=hemisphere which is responsible for lanaguage.
An object is placed in the right hand and the patient is asked to find the object with the same hand
They will be able to find it. This is because the object is processed by the LH which controls the right hand.
2 Strengths for hemispheric lateralisation
Increased neural capacity
By using only one hemisphere to engage in a particular task this would leave the other hemisphere free to engage in another function and thus increasing neural processing capacity.
E.G. Rogers et al. found chicks lacking in lateralisation are slower to detect predators while searching for food.
The experiments involving split-brain patients made use of highly specialised and standardised procedures. There was a high degree of control over all variables and thus increasing the internal validity of the experiment.
COUNTER-ARGUMENT: Many researchers have urged caution in the widespread acceptance of the conclusions drawn from this split-brain research. Split-brain patients constitute such an unusual sample of people. There were only 11 who took part in all variations of the basic procedure, all of whom had a history of epileptic seizures. This may have caused unique changes in the brain that may have influenced the findings lowering the internal validity of the research and making it difficult to draw general conclusions.
2 Limitations for hemispheric lateralisation
Differences in function may be overemphasised..
Modern neuroscientists would contend that the actual distinction between left and right hemisphere is less clear-cut. In the normal brain the two hemispheres are in constant communication when performing everyday tasks, and many of the behaviours associated with one hemisphere can be performed by the other when the situation requires it.
E.G. Patient J.W. developed the capacity to speak out of the right hemisphere with the result that he can now speak about information presented to the left or to the right brain.
This challenges the claim that the right hemisphere is unable to handle language.
Lateralisation changes with age:
Lateralisation of function appears not to stay the same throughout a lifetime, but changes with normal ageing.
Szaflarski et al. (2006)- found language became more lateralised to the left hemisphere with increasing age in children and adolescents, but after the age of 25, lateralisation actually then decreased with each decade of life. Across many types of tasks and many brain areas, lateralised functions found in younger individuals tend to switch to bilateral functions in healthy older adults.
This implies that a lateralised brain is in fact only a feature of young adults and not true for all ages.
