Hemispheric Lateralisation & Split Brain Research Flashcards
What is hemispheric lateralisation?
The idea that the two halves (hemispheres) of the brain are functionally different
& that certain mental processes & behaviours are mainly controlled by one hemisphere rather than the other
e.g. language
What hemisphere is language located in?
Both language centres are in the left hemisphere
- We can say that language is lateralised as its performed in one hemisphere rather than the other
What functions of the brain are not lateralised?
- Vision
- Motor
- Somatosensory centres
All appear in both hemispheres
What is so special about the way the motor centre is wired in the brain?
- Motor area of the brain is cross wired- The RH controls movement on the left side of body while LH controls movement on right side of body
What is so special about the way the visual centre is wired?
Situation is more complex- it is both opposite & same sided
* Each eye recieves light from left visual field & the right visual field
* The LVF of both eyes is connected to the RH & RVF of both eyes is connected to the LH
What is the corpus callosum?
A bundle of nerve fibres which joins the two halves of the brain
The left & right side communicates throught the corpus callosum
What does a ‘split brain’ operation involve?
- Severing the connections between the RH & LH mainly the corpus callosum
- Surgical procedure to reduce epilepsy
What was Roger Sperry’s research?
Devised a system to study how two separated hemispheres deal with for example, speech & vision
What was the procedure of Sperry’s research?
- 11 split brain ppts - ppts were epileptics & could not be treated w drugs- already had their corpus callosum severed therefore no ethical issues in this exp
- An image or word would be projected to a ppts RVF (processed by the LH) & the same or different image could be projected to the LVF (processed by RH)
- In normal brain-corpus callosum would immediately share the info between both hemispheres giving a compelted picture of visual world
- However presenting info to split brain ppt meant that info cannot be conveyed from that hemisphere to the other.
What were Sperry’s findings?
- When a picture of an object was shown to ppts RVF (linked to LH) the ppt could describe what was seen
- But couldn’t do this if object was shown to the LVF (RH)- They said there was ‘nothing there’
This is because in normal brain messages from RH are relayed to language centres in LH but this isn’t possible in a split brain
Although ppts couldn’t give verbal labels to objects projected to LVF they could select matching objects out of sight using thier left hand (linked to RH)
Left hand was also able to select an object that was more closely associated w an object presented to LVF e.g. ashtray was selected in response to picture of cigarette
- If a pinup picture was shown to LVF there was emotional reaction (e.g. a giggle) but ppts usually reported seeing nothing or just a flash of light
Give one strength of Sperry’s research
Sperry’s procedure was a standardised controlled one- has been used multiple times in the same way
With same & different patients & has yielded same results- means that research is reliable & consistent
Means findings & therefore conclusions are valid
Whats one disadvantage for Sperry’s research?
- Limited sample- all epileptics & only 11 ppts
- Could the seizures have changed the brain & therefore the findings?
- This would lead to poor generalisibiliy due to low population validity
Give another strength for Sperry’s research
Research is highly controlled in a labatory which allows for external influences to be eliminated
Data was recorded objectively without bias-means research is highly accurate
Means research has high internal validity
Give one strength for lateralisation
- Research showing that even in normal brains the two hemispheres process information differently
e.g. Fink (1996) used PET scans to identify which brain areas were active during visual processing task
* When normal brain ppts were asked to attend to global elements of an image (such as looking at whole picture of a forest) regions of RH were much more active
* When required to focus on finer deteail (such as individual trees) the specfic areas of LH tended to dominate
Give one limitation of the idea of lateralisation
- The idea that the LH as analyser & RH as synthesiser may be wrong
- May be different functions in the RH & LH but research suggests people do not have a dominant side of their brain which creates a different personality
Nielson analysed brain scans from over 1000 people aged 7-29 & did find that people used certain hemispheres for certain tasks
but there was no evidence of dominant side
e.g. no artists brain/no mathematicians brain
