hemispheric lateralisation and split brain research

• some functions are localised and appear in both left and right hemispheres like auditory, visual and motor areas. The 2 main language centres are in the left hemisphere. The right hemisphere produces rudimentary but provides emotional context. Left visual field of both eyes is connected to the right hemisphere and right visual field of both eyes is connected to the left hemisphere. This enables the visual areas to compare the different perspective from each eye and aids depth perception
• split brain is when 2 hemispheres are surgically separated by cutting the connections like corpus calloum. It is used to treat sever epilepsy to reduce the 'electrical storm' across hemispheres
• Sperry's split brain research procedure: 11 split brain participants were studied by an image or word projected to right visual filed (processed by left hemisphere) and same or different image could be projected to the left visual field (processed by right hemisphere)
• Sperry's split brain research findings: when the object was shown to the right visual field, participants could describe what is seen as language centres are in the left hemisphere. When the object was shown to the left visual field, participants couldn't name the object as there are no language centres in the right hemisphere but they could select matching object behind the screen using left hand and could select object closely associated with picture. For example, ashtray if shown picture of cigarette
• Sperry's split brain research conclusions: this demonstrates how certain functions are lateralised in the brain. It also shows that left hemisphere is verbal and the right hemisphere is 'silent' but emotional
• One strength of lateralised brain function is evidence in 'normal' brains. PET scans show when 'normal' participants attend to global elements of an image, the right hemisphere is more active. When required to focus on finer details specific areas of the left hemisphere tend to dominate (Fink et al.). This suggests that hemispheric lateralisation is a feature of the normal brain as well as the split brain.
• One limitation of hemispheric lateralisation is the idea of analyser versus synthesiser brain may be wrong. Hemispheric lateralisation says that the left hemisphere may be the analyser and the right hemisphere may be the synthesiser. However, there may be different functions in the right hemisphere and left hemisphere but research suggests people don't have a dominant side, creating a different personality. Researchers analysed 1000 brain scans, finding people did use certain hemispheres but no dominance. This suggests that the notion of right or left brained people is wrong.
• One strength of split brain research is support for more recent studies. Researchers showed that split brain participants are better than normal controls. In the normal brain, the left hemisphere's superior processing abilities are 'watered down' by the inferior right hemisphere. This supports Sperry's earlier findings that the 'left brain' and 'right brain' are distinct in terms of functions
• One limitation of split brain research is that casual relationships are hard to establish. In Sperry's research the behaviour of the split-brain participants was compared to a neurotypical control group. However, none of the control group had epilepsy. Any differences between the groups may be due to epilepsy not the split brain (a confounding variable). This means that some of the unique features of the split-brain paritcipants' cognitive abilities might have been due to their epilepsy