Split-brain Research and Hemispheric Lateralisation

Split brain research

  • Sperry and Gazzaniga were the first to investigate hemispheric lateralisation with the use of split-brain patients
  • Split-brain patients are individuals who have undergone surgical procedure where the corpus callosum (which connects the 2 hemispheres) is cut. This procedure was used as a treatment for epilepsy
  • Aim- 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
  • Sperry and Gazzaniga conducted many different experiments- including describe what you see tasks, tactile tests and drawing task
  • In the describe what you seetask, a picture was presented to either the left or right visual field and the participant had to simply describe what they saw.
  • In the tactile test, an object was placed in the patient’s left or right hand and they had to either describe what they felt or select a similar object from a series of alternate objects.
  • Finally, in the drawing task, participants were presented with a picture in either their left or right visual field, and they had to simply draw what they saw
    • Conclusion: the findings of Sperry Gazzaniga’s research highlights a number of key differences between the 2 hemispheres. Firstly, the left hemisphere is dominant in terms of speech and language. Secondly, the right hemisphere is dominant in terms of visual-motor tasks


    • Demonstrated lateralised brain functions
      • Sperry’s pioneering work into the split-brain phenomenon has produced impressive and sizeable body of research findings. Research suggests that the left hemisphere is the analyser whilst the right hemisphere is the synthesiser – a key contribution to our understanding of brain processes.
    • Strengths of the methodology
      • The experiments involving split-brain patients made use of highly specialised and standardised procedures. Sperry’s method of presenting visual information to one hemispheric field at a time was quite ingenious and allowed Sperry to vary aspects of the basic procedure and ensured that only one hemisphere was receiving information at a time.
    • Theoretical basis
      • Sperry’s work prompted a theoretical and philosophical debate about the degree of communication between the two hemispheres in everyday functioning and the nature of consciousness. Other researchers argue that the two hemispheres form a highly integrated system and are both involved in most everyday tasks.
    • Issues with generalisation
      •  Many researchers have urged caution in their widespread acceptance as split-brain patients constitute such an unusual sample of people. The people in Sperry’s study suffered from epilepsy which may have caused unique changes in the brain that may have influenced the findings. The control group Sperry used 11 people who had no history of epilepsy.

    Why is it important that they used a standardized procedure?

    In every step of the research all the participants are treated in exactly the same way and so all have the same experience. This makes the results more reliable. This can be achieved through also having standardised instructions so that it can be repeated easily.


    Would Sperry’s studies have high or low reliability? Why?

    High reliability- lab study- standardised- can be easily repeated.

    Why aren’t more of these studies conducted? How does this affect population validity?

    Population validity is how representative the sample used is to the entire population. As mentioned, split brains are a very rare case and not many people have got split brains. Due to ethical reasons we cannot split someone’s brain just for the sake of the study this there is a limit to how many studies can be conducted on this subject area, which reduces population validity. – surgery rarely carried out like this these days

    Are all split-brain patients the same the same (consider: drug used? Extent of disconnection)? How does this affect validity?

    Not all split-brain patients are the same. This negatively effects validity as the research conducted on split-brain research is therefore not counting for individual differences and thus cannot be totally generalisable. For example, some people may have abused drugs or have had illnesses such as epilepsy which would affect the brain in different ways. Additionally, in cases like Kim Peek, some people can be born with a split brain naturally and this will develop differently and evolve differently to that of someone who had gone through a split-brain surgery.