Hemispheric Lateralisation

• What is Hemispheric Lateralisation?


  The idea that two hemispheres of the brain are functionally different and certain mental processes and behaviours are mainly controlled by one side of the brain and not the other
• What is Contralateral Organisation?


  The idea that the hemispheres control opposite sides of the body
• Give an example of something that is lateralised in the brain

  Language
• For language where are the 2 centres in the brain found?

  1. Broca's area found in the left frontal lobe
  2. Wernicke's area found in the left temporal lobe
• What functions are not lateralised in the brain?

  Motor, vision and somatosensory areas appear in both hemispheres
• Motor Area 


  The right hemisphere controls movement on the left side and the left hemisphere controls movement on the right side
• Visual Area


  When light hits your left visual field the information goes to your right hemisphere and when light hits your right visual field it goes to your left hemisphere
• Corpus Callosum


  A bundle of nerve fibres that connect the left and right hemispheres of the brain
• Split Brain Research

  • Had Corpus Callosum cut so communication between the 2 hemispheres is removed
  • Developed to reduce epilepsy as during seizures electrical impulses are passed from one hemisphere to another
• Sperry's research

  • Used a procedure where an image or word was projected to the patient's right visual field ( which would be processed by the left hemisphere) and another image was projected to the left visual field (processed by the right hemisphere)
  • In split brain research information cannot be transmitted from one hemisphere to another so the effects can be tested
• Sperry: Describe what you can see

  • Picture was presented to right and left visual field and patients had to describe what they saw
  • When the image was in the right visual field they were able to say they saw it as it was processed by the left hemisphere that is responsible for language
  • When the image was in the left visual field they said they saw nothing as it was processed by the right hemisphere that isn't responsible for language
• Sperry: Tactile test

  • Object was placed in left or right hand and they had to describe it
  • When it was in the right hand they could describe the object
  • When it was in the left hand they could not describe the object
• Sperry: Drawing Task

  • Patients were presented with a picture in their right and left visual field and they had to draw what they saw
  • When they saw the pic in their left visual field they could draw what they saw (right hemisphere is responsible for movement)
  • When they saw the pic in right visual field it was hard for them to draw
• What did Sperry's research find in terms of hemispheric lateralisation?

  1. The left hemisphere is responsible for language
  2. The right hemisphere is responsible visual motor skills e.g drawing
• AO3: Highly scientific

  • Sperry's research was highly controlled so the methodology is good
  • Control and standardisation allows it to be replicated
  • This allows more variations to take place to understand more about the brain
  • Less extraneous variables and more valid and accurate
• AO3: Issues with generalisability

  • Sperry's sample involved 11 patients with their corpus callosum removed which is unique
  • This makes the results hard to generalise to the wider population
  • The use of an idiographic approach means that universal laws and general principles cannot be established
  • Hemispheric lateralisation is not a valid explanation
• AO3: Lateralisation changes with age

  • Language becomes more lateralised to the left hemisphere with increasing age in children
  • After the age of 25, lateralisation decreased with each decade of life
  • This raises questions about lateralisation, such as whether everyone has one hemisphere that is dominant over the other and whether this dominance changes with age
• AO3: Language may not be restricted to the left hemisphere

  • A patient suffered damage to the left hemisphere but developed the capacity to speak in the right hemisphere
  • This eventually lead to the ability to speak about information presented to either side of the brain
  • This suggests that perhaps lateralisation is not fixed and that the brain can adapt following damage to certain areas