Lesson 4 Flashcards
What is 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.
What is the role of the corpus callosum?
2 hemispheres are connected via cc.
it is a bundle of nerve fibres which allow info to be communicated by each hemisphere.
we are only able to investigate the different abilities of the two hemispheres when in the treatment of severe epilepsy, surgeons cut the bundle of fibres which forms the cc.
aim was to prevent electrical activity that accompanied epileptic seizures crossing from one hemisphere to the other.
patients who went through this surgery called commissurotomy were referred to as split - brain patients.
What was Sperry and Gazzaniga’s research aim?
they wanted to investigate the extent to which the 2 hemispheres were specialised for certain functions and whether the two hemispheres performed tasks independently of one another.
What was the procedure?
- an image or word was projected to a patient’s visual field (processed by the right hemisphere) or the rvf processed by the left hemisphere).
- ppts fixate on a dot in the centre of the screen and this ensures that info is only presented to the right or left visual field.
- when info is presented to one hemisphere in a split brain patient the info is not transferred to the other hemisphere as the cc has been cut.
sperry and gazzaniga conducted a range of experiments including:
1. describing what they could see
2. recognition by touch
3. drawing tasks
4. composite words
key findings - 1. describe what you see
picture presented in the rvf - processed by left hemisphere
- the patient was able to describe what they saw demonstrating the superiority of the left hemisphere when it comes to language production.
picture presented by the lvf processed by the right hemisphere
- the patient could not describe what was shown.
key findings - recognition by touch
if the object was placed in the right hand (processed by the left hemisphere)
- the patient could describe what they felt verbally.
if the object was placed in the left hand (processed by the right hemisphere)
- patient could not describe what they felt and could only make wild guesses due to no language function to the right hemisphere.
- however, the left hand could identify an object by selecting a similar appropriate object from a series of objects.
key findings - drawing tasks
word represented to the rfv processed by left hemisphere.
- while the right hand would attempt to draw a picture was never as clear as the left hand. However, the patient was able to say the word presented.
- this demonstrates the superiority of the left hemisphere when it comes to language production.
word presented to the lvf processed by right hemisphere
- the left hand would consistently draw clearer and better pictures than the right hand even though all the ppts were right - handed.
- this demonstrates the superiority of the right hemisphere when it comes to visual and motor tasks.
key findings - composite words
two words were presented simultaneously either side of the visual field for e.g. a key on the left and ring on the right.
the patient would say “ring” as that is processed by the left hemisphere and they would be able to pick up they key with their left hand as that was processed by the right hemisphere.
What is the conclusion?
they discovered several differences between the two hemispheres.
left is responsible for speech and language
right is responsible for visual processing and motor tasks.
split brain research suggests the connection between diff regions is just as important as the operation of diff parts.
study evaluation: population validity
limitation of sperry’s research into the split brain phenomena has low population validity.
unusual sample pf people and are rarely encountered in sufficient numbers to be useful for research.
eleven ppts took part in all variations of the basic procedure all of whom had epileptic seizures, it is argued that the disorder of epilepsy itself may have caused changes in the brain that influenced the findings. It is also the case that some PPs experienced more disconnection of the two hemispheres as part of their surgical procedure than others.
this makes it difficult to generalise the findings to a wider population.
study evaluation: standardised procedures
strength of sperry’s research into the split brain is that it followed s.p.
for eg ppts would be asked to stare at a given point the ‘fixation point’. the image would be flashed for a 1/10th of a second.
thus meant that the split - brain patient would not have time to move their eyes across the image and so spread the info across both sides of the visual field and subsequently both sides of the brain. This ensured that only one hemisphere was receiving info at a time.
therefore, due to the scientific rigour of the methodology, sperry’s research into the split - brain phenomena has high internal validity.
theory evaluation: evidence for lateralisation
strength - is that it enables two tasks to be performed simultaneously.
rogers et al found in domestic chickens lateralisation is associated with an enhanced ability to perform two tasks simultaneously (finding food and being vigilant for predators).
allows hemisphere to engage in one task and leaves the other hemisphere free to engage in other functions.
therefore provides evidence for adv of hemispheric lateralisation and demonstrates how it can enhance brain efficiency.
theory evaluation: differences may be overstated
limitation -
sperry simply labels them as ‘verbal’ and ‘non - verbal’
in normal the brain are in communication when performing everyday tasks and many of the behaviours typically associated with one hemisphere can be effectively performed by the other when one hemisphere is damaged.
therefore this suggests that perhaps lateralisation is not fixed and that the brain can adapt following damage to certain areas.
