Split-brain research into hemispheric lateralisation 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
Split-brain studies
a series of studies which began in the 1960s involving epileptic patients who had experienced a surgical separation of the hemispheres of the brain
└this allows researchers to investigate the extent to which brain function is lateralised
Split-brain studies
person
Sperry (1968)
Split-brain studies
background
└all participants had had a commissurotomy (corpus callosum and other tissues that connect the two hemispheres were split down the middle)
└to control frequent severe epileptic seizures
└main connection between too hemispheres removed
└can determine to extent to which the two hemispheres were specialised to certain functions, if they work independently
Split-brain studies
procedure
└image projected to a patients right visual field (processed by left hemisphere)
└another image projected to patients left visual field (processed by right hemisphere)
└in a ‘normal’ brain the corpus collosum would immediately share the information between both hemispheres
└giving complete picture of the visual world
└un split brain patient- information can’t go between hemespheres
Split-brain studies
key findings
list
Describing what you see
Recognition by touch
Composite words
Matching faces
Split-brain studies
key findings
Describing what you see
└picture of object shown to a patients right visual field
└could easily describe it
└picture of object shown to a patients left visual field
└couldn’t describe what was seen- nothing there
└language is processed in the left hemisphere for most
└patients couldn’t describe objects in left visual field (right hemisphere)
└as lack of language centres
Split-brain studies
key findings
Recognition by touch
└patients couldn’t attach verbal labels to object in left visual field
└they could select s matching object from a grab bag with their left hand (right hemisphere)
└objects behind a screen
└couldn’t verbally identify what they had seen
└could select the corresponding object accordingly
Split-brain studies
key findings
Composite words
└if two words were presented simultaneously, one on either side of visual fiend
└e.g key on left and ring on right
└patient would select a key with their left hand and say the word ring
Split-brain studies
key findings
Matching faces
└right hemisphere dominant in recognising faces
└when asked to match a face from a series of other faces
└picture processed by right hemisphere (left visual field) consistently selected, left hemisphere consistently ignored
└when composite picture made up of two halves of a face, one on each hemisphere
└left hemisphere- verbal description
└right hemisphere- selecting a matching picture
Split-brain research into hemispheric lateralisation
strengths
summary
Demonstrated lateralised brain functions
Strengths of the methodology
Split-brain research into hemispheric lateralisation
strengths
Demonstrated lateralised brain functions
└Sperry, later Micheal Gazzaniga
└split brain research
└left hemisphere- analytic, verbal tasks (analyser)
└right hemisphere- only rudimentary words and phrases, bus emotional and holistic content to language (synthesiser)
└key contribution to understanding of brain processes
Split-brain research into hemispheric lateralisation
strengths
Strengths of the methodology
└highly specialised, standardised procedures
└image only flashed up for one tenth of a second
└don’t have time to spread information across both sides of visual fiend (hemispheres)
└allowed Sperry to vary aspects of the basic procedure, ensured only one hemisphere was receiving information at a time
└well controlled, useful
Split-brain research into hemispheric lateralisation
limitations
summary
Theoretical basis
Issues with generalisation
Split-brain research into hemispheric lateralisation
limitations
Theoretical basis
└Sperrys work prompted theoretical/philosophical debate about degree of communication between two hemispheres in everyday functioning/nature of consciousness
└Rodland Pucetti (1977) theorist
└suggested 2 hemispheres are so functionally different they represent a form of duality on the brain
└we are all two minds (only emphasised, not created, in split brain patients)
└other researchers
└two hemispheres form a highly integrated system
└both involved in most everyday tasks
