Split Brain Research Flashcards
What is commissurotomized
Split brain research is used to study brain lateralisation as it shows what functions are dominant for which hemisphere. Here patients who suffer from epilepsy have an operation that involves lesioning (cutting) the nerve fibres of the corpus collusum to stop the seizures. This procedure is known as commissurotomized. This means that the communication between the left and right hemisphere has been cut and thus the two hemispheres are no longer able to communicate with each. Using these patients helps us to study brain lateralisation and whether one hemisphere is more dominant in controlling certain characteristics and behaviours than the other hemisphere
Describe sperry and gazzanigas research
Sperry and Gazzaniga (1967) were the first researchers to study split-brain patients. The researchers would send visual information to just one hemisphere at a time in order to study hemispheric lateralisation – this basically means what types of information is processed specifically by each hemisphere and what are the specialities of each hemisphere
Sperry and Gazzaniga took advantage of the fact that the right hand side of our body is controlled by the left hemisphere and vice versa.
Because the corpus callosum is cut in epileptic patients, how do both hemispheres then process the information since there is no communication between the two!
Aim: The aim of their research was to examine the extent to which the two hemispheres are specialised for certain functions.
Method: Using the ‘divided field procedure’ where 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).
Sperry and Gazzaniga conducted many different experiments, including describe what you see tasks, tactile tests, and drawing tasks.
1. In the describe what you see task, 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.
- 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.
Sperry and gazzanigas findings and conclusion
- In the describe what you see – picture presented to the right visual field (processed by left hemisphere – The patient could describe verbally what they saw – demonstrating the superiority of the left hemisphere when it comes to language production. When the picture presented to the left visual field (processed by right hemisphere) – the patient could not describe what was shown and often reported there was nothing present.
- In the tactile test – objects placed in the right hand (processed by left hemisphere) – the patients could describe verbally what they felt – or they could identify the test object presented in the right hand (left hemisphere), by selecting a similar appropriate object, from a series of alternate objects. When the objects were placed in the left hand (processed by right hemisphere) the patient could not describe what they felt and could only make wild guesses. However, the left hand could identify a test object presented in the left hand (right hemisphere)by selecting a similar appropriate object, from a series of alternate objects.
- In the drawing task, when the picture was presented to the RVF (processed by left hemisphere) while the right-hand would attempt to draw a picture, the picture was never as clear as the left hand, again demonstrating the superiority of the right hemisphere for visual motor tasks.
However when the picture was presented to the LVF (processed by right hemisphere) The left-hand (controlled by the right hemisphere) would consistently draw clearer and better pictures than the right-hand (even though all the participants were right-handed). This demonstrates the superiority of the right hemisphere when it comes to visual motor tasks.
Conclusion: The findings of Sperry and Gazzaniga’s research highlights a number of key differences between the two 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.
Descruve Turk research
A more recent study on split brain patients was carried by Turk et al. (2002) who was interested in face processing after split-brain surgery, in particular whether the patient’s own face was processed in a different way to the familiar face of someone else. The patient was a 48-year-old man (JW) who had a commissurotomy for epilepsy 23 years earlier. He had been extensively tested over the years.
The stimuli were morphed faces; that is, face stimulus made up of two separate faces morphed together. One face was JW’s own, the other was of one of the researchers who had worked with him for a number of years and was familiar to him. A series of morphs were created from 0 percent JW (100 % familiar face), to 50/50 (own/familiar), through to 100 % own (JW).
Researchers used the divided field procedure to present the face stimulus to one or other hemisphere.
In one set of trials, JW was asked to press a button if the image presented was himself, and in another set of trials using the same stimuli, he was asked to press a button if the image presented was the familiar other person.
Turk findings and conclusions
Results showed that the right hemisphere showed that the right hemisphere showed a clear bias towards identifying the morphed faces as a familiar other. On the other hand, JW’s left hemisphere showed a clear bias towards identifying morphed faces as himself.
The researchers accepted that the right hemisphere is generally better at face-processing, but that the left hemisphere may have an important role in self-recognition.
They point out that self-recognition requires personal memories and beliefs and a self-concept, and perhaps the left hemisphere has a primary role in the networks involved in self recognition
Strengths of split brain research
- Through Split Brain research, we can prove that there is hemispheric lateralisation and both hemispheres have different functions – for example the left hemisphere is responsible for speech and language and the right hemisphere is responsible for visual-spatial processing and facial recognition. Also the right hemisphere is seen as a holistic processor whereas left hemisphere breaks information down. This was shown through both Turk’s and Sperry and Gazzaniga’s research. This is a strength because it shows that hemispheric lateralisation exists and this is shown through split brain research
- There is also research support for hemispheric lateralisation through split brain research as shown by Sperry’s studies. For example, the epileptic patients who had split brain surgery and had their corpus collusum cut, struggled with verbally naming an object that was placed in the left hand suggesting language is on the left hand side of the brain. This is a strength as it shows that split brain research also tells us about normal brain functioning. Also, split brain research also shows that the connectivity between the different areas is as important as the operation of the different parts.
Weaknesses of split brain research
Nevertheless split brain research has not shown that the brain is organised into different areas with specific sections responsible for specific tasks.
Sperry’s research was ground breaking and changed our views on hemispheric function and lateralisation. However, there are considerable issues with split brain research such as:
• There are very few patients and only between 10 and 15 have been subjected to extensive study meaning this is a small sample size.
• The sample studies are an extremely varied group – they differ in age and sometimes gender and handedness, age at which they develop epilepsy, age at which they had the split brain operation and age at which they were tested
• The patients operations’ were not always comparable because in some cases not all pathways connecting both hemispheres were always cut allowing for some communication
The above issues pose a threat to the generalisability of split brain research not only to hemispheric lateralisation but also other areas of brain research such as localisation, brain plasticity and functional recovery – therefore we need to be cautious when looking at split brain research. Finally, split brain research is rarely carried out these days due to the fact that modern technology has allowed us to carry out advanced brain scans which do not require brain surgery, so, it may not be relevant in today’s society meaning the research may lack temporal validity.
