Split brain research and hemispheric lateralisation

• Hemispheric lateralisation

  In 1861, Paul Broca established that damage in one particular area of the left hemisphere resulted in language deficits, whereas damage to the same area of the right brain hemisphere did not have the same consequence.

  The connection via the corpus callosum means that we are still able to talk about things perceived by the right hemisphere (eg. face recognition). This allows information received from one hemisphere to be sent to the other hemisphere.
• Visual fields

  = Everything you see to one side of your nose

  LEFT VISUAL FIELD - RIGHT HEMISPHERE - LEFT HAND

  RIGHT VISUAL FIELD - LEFT HEMISPHERE - RIGHT HAND
• Split brain research - Sperry & Gazzaniga (1967)

  • A quasi experiment. 
  • It had 11 participants
  • Sperry’s Pts were epileptics who could not be treated with drugs. They had ALREADY HAD their corpus callosum split. 

  Sperry et al. (1967) were the first to study the capabilities of the separated hemispheres. They were able to send visual information to just one hemisphere at a time in order to study what is known as hemisphere lateralisation.
• Split brain research - Sperry & Gazzaniga (1967)

  Aim: The aim of their research was to examine the extent to which the two hemispheres are specialised for certain functions.

  Method: An image/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). When information is presented to one hemisphere in a split-brain patient, the information is not transferred to the other hemisphere (as the corpus callosum is cut)
• Who conducted the split brain research in 1967?

  Sperry and Gazzaniga
• What types of tasks were included in Sperry and Gazzaniga's split brain research?

  • Describe what you see tasks
  • Tactile tests
  • Drawing tasks
• In the describe what you see task, what was presented to the participant?

  A picture was presented to either the left or right visual field
• What did participants have to do in the describe what you see task?

  They had to describe what they saw
• In the tactile test, what was done with the object?

  An object was placed in the patient’s left or right hand
• What were participants required to do in the tactile test?

  They had to describe what they felt or select a similar object
• In the drawing task, what was presented to the participants?

  A picture was presented in either their left or right visual field
• What did participants have to do in the drawing task?

  They had to draw what they saw
• What year was the split brain research conducted by Sperry and Gazzaniga?

  1967
• What are the three main tasks used in Sperry and Gazzaniga's split brain research?

  1. Describe what you see tasks
  2. Tactile tests
  3. Drawing tasks
• Split brain research - Sperry & Gazzaniga (1967)

  Findings - 

  If a picture is shown to the left visual field, the information is processed by the right hemisphere, but it cannot respond verbally as it has no language centre.

  The left hemisphere doesn’t receive the information and therefore cannot talk about it, despite having a language centre.

  However, the patient will be able to draw it or take it
• Conclusions

  Each hemisphere does have completely separate functions. 

  Left = The left hemisphere is dominant in language 

  Right = The right hemisphere is dominant in visual motor tasks
• AO3 - Evaluation

  (-) split-brain research has limitations as patients who have had this procedure are rare.

  The procedure is rarely carried out nowadays and many studies only included a few Pts or even just one

  These patients may have had underlying physical disorders, or there may have been some intact nerve fibres remaining

  = this means the results of studies are not always replicated, and it may be unwise to draw general conclusions from them.
• AO3 - Evaluation

  (-) lateralisation is not fixed but changes with age for many types of tasks. Healthy older adults have less lateralisation of function, using both hemispheres more as they get older.

  Szaflarski et al. = language lateralisation increase during childhood and adolescence, but decreased steadily after age 25

  = this suggests that older people’s brain recruit both hemispheres to increase their processing power, perhaps to compensate for  age-related cognitive decline.
• Which hemisphere do right-handed people generally develop their language centers in?

  Left hemisphere
• In which hemisphere may left-handed people develop their language centers?

  Either side or both
• Why do neurosurgeons determine which hemisphere is dominant in patients?

  To identify the location of language centers before treatments
• What treatment might neurosurgeons consider when determining the dominant hemisphere for language centers?

  Electroconvulsive therapy (ECT)
• What is the purpose of minimizing cognitive side effects in treatments like ECT?

  To reduce negative impacts on the patient's cognitive function
• What does the variability in language center lateralization imply for generalizations about language processing?

  • Language centers may not be strictly lateralized
  • Individual differences exist in language processing
  • Generalizations about lateralization should be avoided
• What is ECT an abbreviation for?

  Electroconvulsive therapy
• What cognitive side effects might be minimized by understanding language center lateralization?

  Potential memory and language impairments