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
What is the left hemisphere responsible for?
- Controls right side of body
- Responsible for language
- Processes information from right visual field
What is the right hemisphere responsible for?
- Controls left side of the body - Responsible for visual
- motor tasks
- Processes information from left visual field
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
What is a key study which shows evidence for brain lateralisation?
Sperry and Gazzaniga (1968)
What was the procedure of Sperry and Gazzaniga’s study?
- Patients had a split visual field- an image or word is projected to the patient’s left visual field (which is processed by the right hemisphere) or the right visual field (which is processed by the left hemisphere).
- Carried out several tasks:
1) Describe what you see test: a picture was presented to either the left or right visual field and the participant had to simply describe what they saw.
2) Tactile test: an object was placed in the patient’s left or right hand and they had to either describe what they felt, or select a similar object from a series of alternate objects.
3) Drawing test: participants were presented with a picture in either their left or right visual field, and they had to simply draw what they saw.
What was the findings of Sperry and Gazzaniga’s study?
1) Describe what you see tests:
- RIGHT VISUAL FIELD (processed by left hemisphere)= Patient could describe what they saw. Shows the superiority of the left hemisphere when it comes to language production
- LEFT VISUAL FIELD (processed by right hemisphere)= Patient could not describe what was shown and often reported there was nothing present
2) Tactile tests:
- OBJECTS PLACED IN RIGHT HAND (processed by left hemisphere)= patient could verbally describe what they felt
- OBJECTS PLACED IN LEFT HAND (processed by right hemisphere)= patient could not describe what they felt, but they could identify object by selecting a similar appropriate object from series of alternative objects.
3) Drawing tests:
- PICTURE PRESENTED TO RIGHT VISUAL FIELD (processed by left hemisphere and drawn by right hand)= attempt to draw a picture but never clear
- PICTURE PRESENTED TO THE LEFT VISUAL FIELD (processed by right hemisphere and drawn by left hand)= clear pictures consistently drawn even though all patients were right-handed. This shows the superiority of the right hemisphere when it comes to visual motor tasks.
What are the two strengths of hemispheric lateralisation?
Related to increased neural capacity- By using only one hemisphere to engage in a particular task (e.g. language or mathematical ability), this would leave the other hemisphere free to engage in another function and thus increasing neural processing capacity E.G. Rogers et al. (2004)- in the domestic chicken, brain lateralisation is associated with an enhanced ability to perform two tasks simultaneously- finding food and being vigilant for predators. Counter- It is very hard to apply this finding in animals to human brains. There has been very little evidence showing that lateralisation is advantageous to the functioning of the brain in humans.
Scientific methodology- The experiments involving split-brain patients made use of highly specialised and standardised procedures. There was a high degree of control over all variables à increasing the internal validity of the experiment. COUNTER-ARGUMENT: Many researchers have urged caution in the widespread acceptance of the conclusion drawn from this split-brain research. Split-brain patients = 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 à lowering the internal validity of the research and making it difficult to draw general conclusions.
What are the two limitations of hemispheric lateralisation?
Differences in function may be overemphasised- One legacy of Sperry’s work is that it tends to overemphasise and oversimplify the functional distinction between the left and right hemispheres.
Modern neuroscientists 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..
E.G. Patient J.W. developed the capacity to speak out of the right hemisphere. He can now speak about information presented to the left or to the right brain. (This also provides evidence for brain plasticity).
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 (functions tended to be dealt with by one hemisphere) found in younger individuals tend to switch to bilateral functions (functions dealt with by both hemispheres) in healthy older adults.
This implies that a lateralised brain is only a feature of young adults and not true for all ages.
