8. Hemispheric lateralisation

By lateralization, we understand that there is a preferential use or superior function of one side of the brain. The brain exhibits elements of asymmetry itself, although it appears symmetrical. For example, the right hemisphere is thought to be larger and heavier than the left (Heschl, 1878, Schwartz et al 1985), however, Cunningham (1892) proposed that the left occipital lobe was found to be larger than the right. The left hemisphere is rational, verbal, linear and analytiic, whereas the right hemisphere is emotional, spatial and holistic and intuitive ( Bradshaw and Nettleton 1981; Van Lancker 1997). The relationship, however, between anatomical assymetry and functional significance is far from clear ( Beaton 1997).
Myths and Folklore put forward the idea that there are two sides of the brain and that there are differences. The duality of mind model (Wigan 1844) suggests that parts of the brain are more dominant on one side but hemispheres must work together to function properly.
A study on chimeric faces found that the left visual field is processed by the right hemisphere. it occurs not just with the visual stimuli with auditory stimuli too.
Paul Broca (1861) was a physician who performed brain surgeries. Broca found that lesions in the left hemisphere affects language function. Hughlings Jackson (1864) suggests the human brain does not duplicate functions in both hemispheres, however, this is not totally correct.

The two hemispheres have subtle qualitative and quantitative differences. For example, in relation to sound, the left hemisphere is more predominant.
A split brain surgery has no connection between hemispheres in terms of language and speech, a patient with a normal brain, suggest that the right hemisphere has some linguistic abilities. A patient with partial separation found that the right hemisphere match printed words and pictures, but can not match words that rhyme. This suggests that the right hemisphere lacks ability to do phonological decoding. A patient with complete separation suggests that the right hemispheres grammatical abilities match that of a five year old. In relevance to attention, asymettry is not so strong. Depending on the type of the attention, some parts of the brain are more active.
There are also individual differences such as gender. It has been said that males are better at navigating by looking at maps, whereas, women are better at navigating based on landmarks. Women are also better at verbal, memory and language. There is a small difference in object location too.
Research shows that lesions affect lateralisation of function. Split brain surgery is a form of medical procedure which gives the ability to understand hemispheres and its associative functions.