lateralisation + split brain research

• hemispheric lateralisation: the term brain lateralisation refers to the fact that the 2 halves of the human brain are not exactly alike, each hemisphere has functional specialisations i.e. neural mechanisms for some functions (such as language) are localised primarily in 1 half of the brain
• hemispheric lateralisation: e.g. research has found that the left hemisphere is dominant for language and speech whereas the right excels at visual-motor tasks
• hemispheric lateralisation: in 1861 Paul Broca established that damage in a particular area of the left brain hemisphere led to language deficits yet damage to the same area of the right hemisphere didn't have the same consequence
• hemispheric lateralisation: however this raises an important question if language is located in the left hemisphere how can we talk about things that are experienced in the right hemisphere (e.g. face recognition) the answer is that the 2 hemispheres are connected
• hemispheric lateralisation: allowing the information received by one hemisphere to be sent to the other hemisphere through connecting bundles of nerve fibers such as the corpus callosum
• hemispheric lateralisation: the chance to investigate the different abilities of the 2 hemispheres came about when in a treatment for severe epilepsy surgeons cut the bundle of nerve fibers that formed the corpus callosum
• hemispheric lateralisation: the aim of this procedure was to prevent the violent electrical activity that accompanies epileptic seizures crossing from one hemisphere to the other, patients who underwent this form of surgery after often referred to as 'split-brain' patients
• hemispheric lateralisation: the corpus callosum allows the 2 hemispheres to communicate w/ eachother
• split-brain research: Roger Sperry and Michael Gazzaniga (1967) were the 1st to study the capabilities of split-brain patients, to test the capabilities of the separated hemispheres they were able to send visual information to just 1 hemisphere at a time in order to study what is known as hemispheric lateralisation
• split-brain research: Sperry and Gazzaniga took advantage of the fact that information from the left visual field goes to the right hemisphere and information from the right visual field goes to the left hemisphere
• split-brain research: because the corpus callosum is cut in split-brain patients the information presented to 1 hemisphere has no way of travelling to the other hemisphere and can be processed only in the hemisphere that received it
• split-brain research: in a typical study the split-brain patient would fixate on a dot in the centre of a screen while information was presented to either the left or right visual field, they would then be asked to make responses w/ either their left hand (controlled by the right hemisphere) or their right hand (which is controlled by their left hemisphere) w/o being able to see what their hands were doing
• split-brain research: e.g. if the patient was flashed a picture of a dog to the right visual field and asked what they had seen, they would answer 'dog' however if a picture of a cat was flashed to the left visual field the patient would say that they saw nothing
• split-brain research: why is this the case? the information from the left visual field is processed by the right hemisphere but as it has no language centre can't respond verbally
• split-brain research: the left hemisphere which does have a language centre does not receive information about seeing the picture of a cat therefore can't say that they've seen it
• what have we learned from split-brain research?: work w/ split-brain patients has discovered a number of differences between the 2 hemispheres e.g. that the left hemisphere is responsible for speech and language and the right hemisphere specialises in visual-spatial processing and facial recognition
• what have we learned from split-brain research?: however split-brain research has not shown that the brain is organised into discrete regions w/ specific sections responsible for specific tasks instead it suggests that the connectivity between the different regions is as important as the operation of the different parts
• evaluation S: this is natural experiment and is the only ethical way to investigate the isolation of the hemispheres
• evaluation S: the research is very useful as it shows lateralisation of function exists
• evaluation L: Sperry's work was based on only a few patients who had experienced long-term problems w/ epilepsy, these factors might limit generalisability from this sample to the population
• evaluation L: the split-brain procedure is rarely carried out nowadays and Andrewes (2001) points out that many studies are presented w/ as few as 3 participants or even just the 1 single participant, so patients who have had this procedure w/o these confounding factors are rarely encountered in sufficient numbers to be useful for research