Hemispheric Lateralisation

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  • Created on: 31-05-22 13:45
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  • Hemispheric lateralisation
    • Hemispheric lateralisation is the theory that the two halves or hemispheres of the brain are functionally different and certain mental processes and behaviours are mainly controlled by one hemisphere rather than the other
    • Split brain research
      • Sperry’s research involved a unique group of individuals who had undergone commissurotomy. This is where the corpus callosum which connects the two hemispheres had been cut to separate the two hemispheres. 
        • This was done to control epileptic seizures but allowed Sperry to study people whose hemispheres had now been separated to see the extent to which each hemisphere was specialised and which brain functions are lateralised.  
      • Procedure
        • An experimental situation is set up with a split visual field: Image/word is projected to the patient’s right visual field and the same, or different, image could be projected to the left visual field.
          • The researchers did this by blindfolding one eye and then flashing images/words on the screen for 1/10th of a second meaning the patient wouldn’t have time to move their eye across the image to spread the information across both visual fields. 
            • TASK FOR PATIENT: the patient either; stated the word they had seen or wrote the word or matched the word with an object.
      • Findings
        • Patients could describe what they saw if the image was projected to the right visual field however they were unable to do this if it was projected to the left visual field. 
        • Patients could not attach verbal labels to objects presented to the left visual field 
        • When patients were presented with two words presented simultaneously e.g. key on the left and ring on the right- see image, patients would write the word key with their left hand, or select a key from a group of objects and say the word ring.  
        • Language is lateralised to the left hemisphere, Drawing and face recognition is lateralised to the right hemisphere. 
      • P - Lateralisation theory is reductionism.
        • E - Lateralisation research has led to the development of ‘pop-psychological’ literature and oversimplifies the distinction between the left and right hemispheres. 
          • E -  Differences in the functions may be overstated and may be less clear-cut. 
            • L - This means that a more holistic approach to understanding brain organisation might be more appropriate.
      • P -There are other explanations for brain function organisation.
        • E - Others argue the left and right hemispheres are in constant communication and highly integrated and work together in most tasks.
          • E - Research into neural plasticity has demonstrated that functions typically associated with one hemisphere can be effectively performed by the other.  For example, following trauma unaffected areas of the brain take over lost functions.
            • L - This means that lateralisation theory may not be a complete explanation of brain functions.
      • P -  Sperry’s research was incredibly influential to the understanding of neuroscience.
        • E - His research led to a substantial body of research being published about lateralisation of functions in the brain. 
          • E - For example, language/verbal tasks on the left side of the brain and drawing/face recognition on the right side of the brain. 
            • L - This means that Sperry’s findings have had positive implications for informing therapies for individual’s with brain damage limited to one side of the brain.
      • P -  Sperry’s research was controlled and conducted in a laboratory environment
        • E - He used standardised procedures of presenting visual information to one hemispheric field at a time.
          • E - For example asking participants to stare at a ‘fixation point’, flashing the image for 0.1 second. He also blindfolded one eye of his participants to ensure information was only being received by one hemisphere.
            • L - This means he could be confident in the conclusions he was making about hemispheric lateralisation, as it was a well-controlled procedure.


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