Hemispheric lateralisation and split brain research Flashcards
Hemispheric lateralisation
Each hemisphere of the brain (right/left) is specialised to perform different functions (language centres are in the left hemisphere, visuospatial tasks are best performed by the right)
What does localised mean?
Specific parts of the brain control specific aspects of brain function
Some functions are localised and appear in both left and right hemispheres
e.g auditory, visual, motor, somatosensory areas
What does lateralised mean?
Functional dominance of one hemisphere over the over, which one is more responsible or entirely responsible for control of a function in comparison to the other
Contralateral vs ipsilateral
Contralateral means controlling the opposite side
Ipsilateral means controlling the same side
Introduction on split brain
Cutting the corpus callosum is a surgical procedure for epilepsy. Isolating each hemisphere from the other.
The corpus callosotomy reduces epileptic symptoms and has few side effects for such invasive procedure. However unusual behaviour and a sense of a loss of agency (feeling of control) led to research
Describe the procedure of Sperry’s split brain research
11 split brain participants were studied. An image or word was projected to the right visual field (processed by left hemisphere) and same, or different, image could be projected to the left visual field (processed by right hemisphere)
Presenting the image to one hemisphere meant that the info could not be conveyed from that hemisphere to the other
What were the findings and conclusions of Sperry’s split brain research
Object shown to RVF - participant can describe what is seen (language centres in LH)
Object shown to LVF:
- Cannot name object (no language centres in RH)
- Can select matching object behind screen using left hand
- Can select object closely associated with picture
Demonstrates how certain functions are lateralised in the brain, shows that LH is verbal and the RH is ‘silent’ but emotional
EVALUATION: An advantage - neural processing
The main advantage of brain lateralisation is thought to be an increase in neural processing capacity, or the capacity to handle several activities at once.
According to Rogers et al. (2004), lateralisation of the brain in domestic chickens is linked to improved dual task performance (searching food and keeping an eye out for predators). When one hemisphere is solely utilised for a task, the other hemisphere remains available for other purposes.
This shows how brain lateralisation can improve brain efficiency in cognitive activities and offers evidence for its benefits.
EVALUATION: Lateralisation of function changes with aging
In healthy adults, lateralised patterns found in younger individuals convert to bilateral patterns across a wide range of tasks and brain regions.
In children and teenagers, language grew more lateralized to the left hemisphere with age; however, beyond age 25, lateralization declined with each decade, according to research by Szaflarski et al. (2006).
It is unclear why this is the case, but one theory is that age-related functional reductions may be partially offset by harnessing the additional processing power of the other hemisphere.
EVALUATION: Methodological criticism
The split brain technique is rarely conducted today, making patients hard to come by, which unfortunately means that much of the study on lateralisation is flawed.
Sperry’s research consisted of only 11 patients, all of whom had varied degrees of epilepsy. These investigations typically involve very few participants. Therefore, some psychologists have argued that Sperry’s work is actually a collection of case studies using an idiographic approach.
Unlike nomothetic research, which allows us to create general laws or apply the findings, an idiographic technique only allows us to obtain rich and interesting information about specific cases.
This is important because any findings reached will only apply to those patients who had a physical condition that required the treatment that made the procedure necessary - results cannot be generalised to wider population
EVALUATION: Language in the right hemisphere
It could be argued that language may not be left hemisphere specific.
Turk et al found a patient who had left hemisphere damage but subsequently recovered the ability to speak in the right hemisphere regarding information coming from either side of the brain.
Consequently, it implies that the brain may be able to adapt after suffering damage to certain areas and that lateralisation may not be fixed.
