Lateralisation

• What are the weaknesses of research into hemispheric lateralisation?

  Research only observes a small number of patients, so in order for results to be generalised to society a wider sample size is needed, furthermore all of these patients had brain abnormalities which may act as a confounding variable.

  
  

  Another weakness of this study is that the findings have not been replicated e.g. more recent studies have shown that not all aspects of language are controlled by the left hemisphere. Additionally, there are case studies that are exception to this theory e.g. patient EB had his left hemisphere removed at 2.5 years old, initially loosing his language skills however after rehabilitation he regained this skills disproving the concept of it being hemispherically lateralised.
• What is the evidence for hemispheric lateralisation?

  Evidence for hemispherical lateralisation comes from split brain research from patients who have had their corpus callosum cut meaning that the hemispheres can no longer communicate with eachother, this was used as a treatment for people suffering with extreme epilepsy.

  
  

  Patients reported very few side effects from the treatment, however, they did say that they felt like they had the strange sensation that they were two people inside one body.

  
  

  Sperry 1968 conducted an experiment, presenting stimuli to either the left or right hemisphere of 11 patients, asking them to pick out the object/stimulus from a group, either describing or pointing it out.

  
  

  Sperry found that if patients were asked to identify the stimulus from a group it was only successful when presented to the right hemisphere, and when patients were asked to verbally describe the image the task was only performed successfully if the image ws presented to the left hemisphere.

  
  

  From this, Sperry concluded that language skills are hemispherically lateralised to the left and spatial to the right.
• Can functions be performed by both hemispheres but not contralaterally?

  Yes, hearing smell and taste.
• What does contralateralisation mean?

  Some functions are organised contralaterally meaning that the left hemisphere controls the right side of the body and the right hemisphere controls the left side.

  
  

  E.g. vision, body movement and touch.
• What is hemispheric lateralisation?

  the idea that the left and right hemisphere perform different functions.

  
  

  E.g. language skills are hemspherically lateralised to the left, and spatial skills are hemispherically lateralised to the right.
• How is the brain divided?

  The brain is divided into two halves called hemispheres connected by the corpus callosum which is a bundle of axons that enables communication between the two.
• What is brain lateralization?

  the idea that different parts of the brain perform different functions.
• Split brain research

  Sperry et al aimed to prove hemispheric lateralisation. He used 11 patients who had all undergone split brain surgery in attempt to reduce their severe epilepsy. He used various tasks to research, one being blindfolding one of a ppts eyes and flashing an image so fast the eyes did not have time to move - which is important as if it was not quick enough, it would spread he visual information across the brain. He found that even if ppts could not express what they saw verbally, they could draw it. He concluded that, as the right brain has no language function, it could not say what it saw, but it could control the left side of the body to draw it - proving both hemispheric lateralisation and that the human brain is contralateral.