Biopsychology: Lateralisation and split - brain research Flashcards
What is hemispheric lateralisation?
Hemispheric lateralisation is the idea that the two hemispheres of the brain are functionally different and that certain mental processes are mainly controlled by one hemisphere.
Information in the left visual field goes to the…
Information in the right visual field goes to the…
Right hemisphere
Left hemisphere
What is the link between the two hemispheres?
The two hemispheres are connected by something called the corpus callosum (a bundle of nerve fibres that connect the two halves)
What was Sperry’s procedure?
He devised a procedure where an image or word was projected to a patient’s right visual field (processed by the left hemisphere) for 1/10 of a second and the same or different image was projected to the left visual field. The patient would then be asked to make a response with their left hand, right hand or verbally.
What were the results of Sperry’s research?
When a picture was shown to a patient’s right visual field the patient could easily describe what was seen. However, if the same image was shown to the left visual field the patient could not describe what was seen. This is because messages from the right hemisphere are usually related to the language centres in the left hemisphere but the corpus callosum which connects both hemispheres were cut.
Findings: Describing what they see - Sperry’s research
When a picture of an object was shown to a patient’s right visual field they could easily describe what was seen because the right visual field is processed by the left hemisphere and the left hemisphere has a language centre. When a picture was presented to the left field of vision they could not describe it and often reported that there was nothing present because the right hemisphere doesn’t have a language centre so cannot respond verbally.
Findings- recognition by touch - Sperry’s research
When the object was placed in the right hand and processed by the left hemisphere the patient described verbally what they felt. Or they could identify the test object presented in the right hand, by selecting a similar appropriate object, from a series of alternative objects.
When the object was placed in the left hand and processed by the right hemisphere the patient could not describe what they felt or could only make a wild guess. However, the left hand could identify a test object presented in the left hand, by selecting a similar to an appropriate object, from a series of alternate objects.
What was the conclusion of Sperry’s research?
- The left hemisphere is broadly responsible for speech and language.
- The right hemisphere is responsible for visual-spatial processing and facial recognition. Does not show how the brain is organised into discrete regions with specific sections responsible for specific functions.
- Instead suggests that connectivity between the different regions is as important as the operation of the different parts.
A03: Sperry’s research - Hemispheric lateraliation
+ Advantages of research into lateralisation
+ Practical applications of the research
- Generalising findings from the research is difficult
- Lateralisation changes over time with age
A03: Advantages of research into lateralisation
A strength of Sperry and Gazzaniga’s research is that it was an innovative and ingenious method that allowed psychologists to scientifically study split-brain patients. Due to the unique nature of split-brain cases, scientists previously had difficulty conceiving a standardised method in which all split-brain patients could be investigated. Sperry and Gazzaniga’s original method of blindfolding one eye and asking participants to fixate on a dot while an image is flashed for 1/10th of a second, allowed for an objective and operationalised method that could be replicated. Therefore, due to the scientific nature of the methodology, the validity of the findings is increased.
A03: Practical applications of the research
A strength of research into hemispheric lateralisation is that it has practical application. For example, Sperry and Gazzaniga’s conclusions about the functions of the left and right hemispheres can be applied to specifically designed rehabilitation programmes that focus on verbal and visuospatial therapy for people who have brain damage. Understanding lateralisation could help those gone through damage perform specific tasks to accelerate the rate of recovery. Therefore, research into lateralisation is useful to help improve lives.
A03: Generalising findings from the research is difficult
A weakness of research into lateralisation is that it cannot be easily generalised. For example, in Sperry and Gazzaniga’s experiment, all 11 participants had a history of epileptic seizures. While all participants has their corpus callosum damaged, some had other connections between the left and right hemispheres still intact. This is a problem as epilepsy could have affected their brains in different ways and their brain activity cannot always be generalised to people without epilepsy. The inconsistency of the disconnection shows the participants had individual differences, which could have affected the internal validity. Therefore, the conclusions that Sperry and Gazzaniga derived may be invalid.
A03: Lateralisation changes over time with age
A weakness of the concept of lateralisation is that research has found that lateralisation changes with age. For example, Szaflarski et al. found that language became more lateralised to the left hemisphere throughout childhood and adolescence but after the age of 25, lateralisation decreased with every decade. This shows that our brain does not work in the same lateralised way throughout life. The fact that it changes with age makes us question Sperry and Gazzaniga’s conclusions. This is because if lateralisation is the brain’s way of functioning, it should be demonstrated by everyone, regardless of age. Thus lacking validity as it assumes that each hemisphere is definitive in its functions.
