Hemispheric Lateralisation

• The brain is made up of 2 hemispheres, the left and right.
• The left hemisphere is associated with language and logic.
• The right hemisphere is associated with recognition and spatial awareness.
• Individuals can be left or right dominant in the brain, or bilateral.
• Individuals who are left brain dominant are believed to be better at maths and science.
• Individuals who are right brain dominant are believed to be better at sports, creative arts or practical subjects.
• Lateralisation of brain function is the view that distinct brain regions perform certain functions.
• If a certain area of the brain becomes damaged, the function associated with that area will also be affected.
• The human brain is split into 2 hemispheres, right and left. They are both joined together by the corpus callosum, a bundle of nerve fibres which is located in the middle of the brain.
• Hemispheric lateralisation is the idea that each hemisphere is responsible for different functions. Each of these functions is localised to either the right or left side.
• The left hemisphere is associated with language functions, such as formulating grammar and vocabulary.
• The right hemisphere is associated with more visuospatial functions such as visualisation, depth perception, and spatial navigation.
• In an outdated treatment for severe epilepsy, the corpus callosum was severed, meaning the connections between the two hemispheres were prevented. This is known as split brain surgery.
• Roger Sperry conducted experiments on split-brain patients to test whether there was a localisation of function in the hemispheres.
• Gazzaniga (1983) conducted an experiment using faces projected to both visual fields (VF). It was found that faces on the left VF, projecting to the right hemisphere, were recognised but could not be named.
• Tomasi & Volkow (2012) found that males had increased right lateralisation of connectivity in areas of the temporal, frontal, and occipital lobes. In contrast, females had increased left lateralisation of connectivity in the left frontal lobe.
• Phineas Gage supports the localisation of functions theory as it shows that control of social behaviour/ personality is located in the frontal lobe.
• Sperry & Gazzaniga (1967) highlights a number of key differences between the two hemispheres. Firstly, the left hemisphere is dominant in terms of speech and language. Secondly, the right hemisphere is dominant in terms of visual-motor tasks.
• Sperry (1968) devised a system to study how the 2 hemispheres deal with information from visual and tactile tasks.
• Sperry (1968) studied split brain patients using a tachistoscope and support the idea of hemispheric disconnection.
• Sperry (1968) supports the idea that certain functions are lateralised in the brain.
• Fink et al (1996) used PET scans to identify areas of the brain which are active during a visual processing task. They found a specific area in the brain dedicated to this.
• Nielson et al (2013) studied brain scans from over 1000 people and found no evidence for lateralisation.
• Rogers et al (2004) showed that lateralised chickens could find food while looking out for predators, while normal chickens could not.
• Luck et al (1989) showed that split brain patients performed better on certain tasks than a normal control group.
• Split brain research is limited to small sample sizes which cannot be generalised.
• Sperry's split brain experiments.

  
• Sperry (1968) found that objects presented to the right visual field (RVF) could be described using language, as it is processed in the left hemisphere. Objects presented to the left visual field (LVF) could not because the right hemisphere has no language centres.
• Sperry (1968) also conducted tactile tests on split brain patients and found that participants could pick up objects in their right hand and recognise if they had picked it up before, but they could not say what it was.
• The right hemisphere is not involved in language processing and has no language centres.
• The left hemisphere is responsible for language functions, such as formulating grammar and vocabulary.
• Damage to the left hemisphere can result in language impairments, such as aphasia.