Split brain research

• Hemispheric lateralisation is the idea that the 2 halves of the brain are functionally different. Also certain mental processes/behaviours are mainly controlled by one hemisphere rather than the other.
• Split-brain research is a series of ongoing studies, which started in the 1960's where epileptic patients underwent a commissurotomy (corpus collosum lesioned), separating the 2 hemispheres. This allowed researchers to study the extent of brain lateralisation.
• Localisation refers to the fact some functions such as vision and language are governed by very specific areas in the brain.
• Brain is lateralised I.e there are 2 sides called hemispheres (hemispheric lateralisation). Some functions the localised areas appear in both hemispheres e.g. Vision is in the left and right occipital lobe - located in LH and RH respectively.  
• In case of Lang, the 2 main centers are only in LH for most ppl - Broca's area is in the left frontal lobe and Wernicke's area is in the left temporal lobe. Therefore, Lang is lateralised as it's being performed by 1 hemisphere rather than other. RH can only produce rudimentary words/phrases but contributes emotional context to what is being said. Led to suggestion LH is analyser while RH is synthesiser.  
• Which three processes aren't lateralised? 


  Vision, motor and somatosensory area as they appear in both hemispheres.  
• There is contralateral wiring in motor area in which the RH controls movement on the left side of body whilst LH controls movement on right.
• In vision, it is both contralateral and ipsilateral. Each eye receives light from the LVF and RVF. LVF of both eyes is connected to RH and RVF of both eyes is connected to LH. Enables visual areas to compare slightly diff perspective from each eye and aids depth perception.   
• Sperry conducted a quasi-experiment on 11 patients who had undergone a commissurotomy to control frequent and severe epileptic seizures. Therefore, the main communication line between the two hemispheres was removed. This allowed Sperry to determine which hemispheres were specialised for certain functions, and whether the hemispheres performed tasks independently
• Procedure - image or word would be projected to a patients right visual field, processed by the left hemisphere, and the same or different image, would be projected to a patients left visual field, processed by the right hemisphere. In a normal brain the CC would have shared the information with the other hemisphere, giving a complete picture of the visual world. Presenting information to just one hemisphere meant it could not be shared in split-brain patients, as the CC is removed.
• Sperry Findings - when pic/object shown to patient RVF they could easily describe what they'd seen but they couldn't with RVF as Lang centres are in LH so when image is presented in LVF, it is processed in RH which has no long centre and the corpus collosum is absent so info isn't shared by LH.
• Sperry Findings - Although p's could not give verbal labels to objects projected to the LVF, they could select a matching object out of sight using their left hand (linked to RH). The left hand was also able to select an object that was most closely associated with an object presented to the LVF (for instance, an ashtray was selected in response to a picure of a cigarette).
• Sperry findings-composite words If two words were presented at the same time, one on either side of the visual field, the patient would write the word 'key' with their left hand (the RH has superior drawing ability), and say the word 'ring" (as the RVF Is processed in the LH which has the language centres).
• Sperry findings-matching faces The RH appears dominant for face recognition. When asked to match a face from a series of other faces, the picture processed by the RH (LVF) was consistently selected, whereas the pictures presented to the LH (RVF) were ignored. When a composite picture made up of two different halves of a face was presented with one half to each hemisphere, the LH domminated in verbal description but RH dominated in selecting a matching pic
• S - Sperry's and Gazzaniga's work into split brains has been well supported by research, the conclusion of which is that the LH is more geared toward analytic and verbal tasks, while RH is better at performing spatial tasks and music. The RH produces rudimentary words and phrases, but contributes emotional and holistic content to language. The LH is the analyser and the RH is the synthesiser.
• However, according to Nielsen et al (2013) this may not be correct. Analysed brain scans from over 1000 ppl aged 7-29 yrs and didn't find people use certain hemispheres for certain tasks. But no evidence of dominant side I.e. The artist brain or mathematicians brain suggesting notion of right and left brained ppl is wrong.  
• Strengths of the methodology: The split brain studies used highly specialised and standardised procedures e.g. Presenting a fixation point for less than 1/10 of second which allowed him to ensure that P's were only able to see an object in one visual field at a time I.e. blindfolding one of p's eye, and not the other. This allowed him to vary aspects of the procedure so only one hemisphere was receiving information at any one time.
• Evaluation - Others have argued that the two hemispheres form a highly integrated system and are both involved in most everyday tasks. They argue that most everyday tasks involve a mixture of 'left' and 'right' skills, (e.g. in listening to speech we analyse both the words and the pattern of intonation) thus, rather than 'doing their own thing' the two hemispheres work very much together.
• Issues with sperry generalisation:

  • Small sample (11ps)
  • All had history of epilepsy, may have caused unique changes in Brain influencing findings
  • Some patients had experienced more disconnection than others due to varying amounts of corpus callosum lesioned
  • Lack of ecological validity - findings unlikely to be found on real life situations as both hemispheres would have access to info
• Gazzaniga found when each hemisphere of split-brain patients were presented with faces, the RH was much more able to recognise them suggesting RH is specialised for facial recognition.