Hemispheric Lateralisation & Split brain research BP Flashcards
hemispheric lateralisation
the idea that the two halves (hemispheres) of the brain are functionally different and that certain mental processes and behaviours are mainly controlled by one hemisphere rather than the other, as in the example of language
split-brain research
a series of studies which began in the 1960’s involving people with epilepsy who had experienced a surgical separation of the hemispheres of their brain to reduce the severity of t
contralateral wiring
right hemisphere controls movement on left side and vise versa
Localisation
Some functions like vision and language are localised to specific areas of the brain.
lateralisation
There are two sides of the brain called hemispheres (lateralised).
language
- Mostly left hemisphere
- Broca’s area (left frontal lobe)
- Wernicke’s area (left temporal lobe)
- Language is lateralised
- Right hemisphere contributes emotional context to what is being said
vision
- Not lateralised
- Contralateral and ipsilateral (opposite and same-sided)
- Both eyes receive light from both visual fields
- Left visual field of both eyes is connected to the right hemisphere
- Right visual field of both eyes is connected to the left hemisphere
- This aids depth perception and comparison of different perspectives
non-lateralised functions:
- Vision, motor, somatosensory areas
- In motor area, brain is cross-wired (contralateral wiring)
Sperry’s research:
Study how two separated hemispheres deal with speech, vision
Sperry’s procedure
- 11 people who had split-brain operation were studied (image projected to participants right visual field and vice versa)
- In ‘normal’ brain, the corpus callosum would immediately share information between both hemispheres (complete image of the world)
- However, on split-brain participants information cannot be conveyed from that hemisphere to the other
sperry’s fidnings
When picture of object was shown to right visual field, participants could describe what could be seen
Could not be seen if on LVF - ‘nothing was there’
* Due to the relaying of messages fro, RH to LH, and isn’t possible in split-brain
* No verbal labels to objects
* But could select matching objects out of sight
Sperry’s conclusion
Certain functions in the brain are lateralised
Lateralisation in the connected brain
I:
strength
The two hemispheres process information differently
Fink et al used PET scans to see which areas were active during a visual processing task
Lateralisation in the connected brain
D:
strength
When looking at the picture as a whole the RH was more active
LH for more active for finer details
Lateralisation in the connected brain
E:
strength
For visual processing, hemispheric lateralisation is a feature of the connected brain and the split-brain
One brain
I:
limitation
The theory that LH as analyser and RH as synthesiser may be incorrect and the research has lead to the erroneous pop-psychology notion that people are left or right brained
One brain
D:
limitation
Nielsen et al analysed 1000 brain scans from people aged 7-29 and found evidence for lateralisation
But no evidence for a dominant side
One brain
E:
limitation
The notion of right or left brained people is wrong
Lateralisation versus plasticity
Lateralisation is adaptive as two tasks can be performed at the same time (supported by Rodgers et al, who found that lateralised chickens can find food and watch predators but other chickens can’t)
Neural plasticity is also adaptive as after damage to an area, some functions can be taken over by non-specialised areas (Holland et al)
Split-brain research support
I:
strength
More recent split-brain research
Split-brain research support
D:
strength
Gazzaniga showed that split-brain participants actually perform better than connected controls on certain tasks
Faster identifying the odd one out in an array of similar objects
Split-brain research support
E:
strength
Left and right side differ in terms of functioning
Generalisation issues of split brain research
I:
limitation
Limitation of Sperry’s research is that causal relationships are hard to establish
Generalisation issues of split brain research
D:
limitation
- Split-brain ppts were compared to a neurotypical control group
- None of the ppts in control group had epilepsy
- This is major confounding variable
Generalisation issues of split brain research
E:
limitation
Any differences might have been due to the epilepsy rather than the split-brain
