Hemispheric lateralisation and split-brain research Flashcards
What is hemispheric lateralisation?
The 2 halves of the brain are functionally different, and certain mental processes are controlled mainly by one hemisphere
What is split-brain research?
Studies involving people with epilepsy who experienced a surgical separation of the brain’s hemispheres to reduce the severity of their epilepsy
How is language lateralised?
- Performed by one hemipshere (left)
- RH only produces rudimentary words/phrases but contributes but contributes emotional context
What are some examples of functions that are not lateralised?
- Vision
- Motor area
- Somatosensory area
What is the role of the RH and LH?
RH= synthesiser
LH= analyser
What occurs in the motor area?
- The brain is cross-wired (contralateral wiring)
- RH controls movement on the left side
- LH controls movement on the right side
What is vision classed as?
- Contralateral (cross-wired)
- Ipsilateral (opposite, same sided)
How is light received?
- Received from left visual field AND right visual field
- LVF is connected to RH
- RVF is connected to LH
- Visual areas compare the different perspectives from each eye- aids depth of perception
Strength:
I- Lateralisation in the connected brain
Lateralisation
D- Fink et al used PET scans to identify which areas of the brain are active during a visual processing task. Connected brain participants attended to global elements of an image, and the RH was active
E- Suggests hemispheric lateralisation is a feature of both the connected and split brain
Limitation
I- One brain/pop-psychology
Lateralisation
D- RH as synthesiser and LH as analyser may be incorrect. Research suggets there is not a dominant side of the brain. Nisan et al analysed brain scans of 1000+ people aged 7-29. Found people used certain hemispheres for specific tasks but there was no evidence of a dominant side
E- Supports idea that right/left brained people is wrong
Evaluation extra- Lateralisation vs plasticity
Lateralisation
Strength: Lateralisation provides an adaptive function. Rogers showed that chickens with lateralised brains could find food, whilst looking for predators. Chickens reared in the dark, with non-lateralised brains could not do this. Lateralsiation is the 1st preference
Limitation: Neural plasticity seen as adaptive. After trauma/damage, non-specialised areas take over functions. Holland- language ‘switches sides’. Lateralised functions are flexible not fixed
What do split-brain operations do?
- (Commisurotomy)
- Sever the connections between LH and RH (corpus callosum)
- Procedure to reduce epilepsy
What does the right hemisphere do?
- No language
- Has understanding
- Facial recognition
- Synthesiser (whole picture)
What does the left hemisphere do?
- Language
- Analyser (details of picture)
What did Sperry study?
- Studied how 2 hemispheres deal with speech and vision
What was Sperry’s procedure?
- 11 split-brain patients (commissurotomy) were studied
- Stare at fixation point on screen
- Image/word was flashed on screen for 1/10 of a second
- Participants asked to say/draw what they saw
What did Sperry find?
- When image shown to RVF, patient could describe what they saw
- Image shown to LVF, could not describe
- Participants couldn’t give verbal labels to LVF objects but could select matching object using left hand
- When pinup picture was shown to LVF, emotional reaction (giggle) but claim they saw nothing
What did Sperry conclude?
- Certain functions are lateralised in the brain
- Supports the view that LH is verbal (analyser) and RH is silent but emotional (synthesiser)
Strength:
I- Research support
Split-brain research
D- Gazzaniga- split brain patients perform better than control on certain tasks. E.g: faster at identifying the odd one out than control group. Kingstone- In normal brain, LH’s cognitive strategies are watered down by RH
E- Supports Sperry’s findings that left and right brain differ
Limitation:
I- Generalisation issues
Split-brain research
D- Hard to establish causal relationships. Split-brain patients (Sperry) were compared to neurotypical group.Differences may be result of epilepsy not split-brain
E- Means some unique features of split-brain patients’ cognitive abilities have been due to some epilepsy
Strength:
I- Highly reliable
Split brain research
D- Images/words were flashed up for 1/10 of a second, preventing participants’ eyes moving. This allows the image/word to go to one hemipshere only
E- Means research is highly standardised and can be reliably replicated
I- Ethical issues
Evaluation extra
- Harm was not deliberate- participants had already had their corpus callosum cut out
- Trauma of operation meant patients did not understand implications of what they agreed to (stress, strain of testing)
