Hemispheric Specialisation and Dominance in Language Processing and Production
This experiment investigated hemispheric specialisation and dominance with regards to language functions. It used a computer program to measure the amount of key presses achieved by participants in a given time across four different trials (1 with the left hand, no talking, 2 with the left hand whilst being asked questions, and the same two trials again with the right hand). The participants were 2nd year psychology students from which a cohort of 20 was selected for data analysis. A significant difference was found for the effect of hemisphere and language processing task present or absent. However, the means for each trial did not support left hemispheric dominance for language functions: more key presses were recorded when talking and using the right hand than when talking and using the left. Handedness and some involvement of the right hemisphere in language processing and production were also shown as appearing to influence the results obtained. The main conclusion to be drawn is that hemispheric specialisation and language dominance is a subject that needs further investigation in order to clarify the generalisability of conclusions made about left hemisphere language specialisations.
Our brain consists of two halves; the left hemisphere and the right hemisphere. The left hemisphere receives information from and controls muscles in the right side of the body, whilst the right hemisphere receives information from and controls muscles in the left side of the body. Research using brain imagery and studies of brain damaged and split brain patients, to name just a few examples, has shown that some of our functions are controlled more by one hemisphere than the other, i.e. are more specialised for that particular function.
This experiment aims to investigate these differing specialisations of the hemispheres more deeply and with particular regard to language.
Research into language differences between the two hemispheres is widespread and supports the view that the left hemisphere is the more dominant.
Marc Dax was the first to notice hemispheric differences in his brain damaged patients, after having seen many patients suffering from loss of speech. Dax found what appeared to be an association between the loss of speech and the side of the brain where the damage occurred. ‘In more than 40 patients with aphasia, Dax noticed damage to the left hemisphere; he was unable to find a case that involved damage to the right hemisphere alone’ (Springer and Deutsch, 1998, p.1-2).
By 1870 further evidence also began to surface, when other investigators began to realise that ‘many types of language disorders could result from damage to the left hemisphere’ (Springer & Deutsch, 1998, p.1). For example, Broca’s and Wernicke’s aphasia: Broca’s aphasia causes speech problems associated with comprehension, resulting from damage to Broca’s area (situated in the left frontal cortex), whilst Wernicke’s aphasia causes word salad (hard to understand, jumbled speech), resulting from damage to Wernicke’s area (situated in the left temporal lobe).
Later research has also supported Dax’s original findings, one example of such research concluded ‘that the left hemisphere is responsible for language in almost all right-handed individuals’ (Butler, S.R. 1997, p. 187). This research also links the additional factor of handedness to investigations of hemispheric lateralisation, an idea which has been supported by others in the field.
For example: ‘In right handers …, it is almost always the case that the hemisphere that controls the dominant hand is also the hemisphere that controls speech’ (Springer and Deutsch, 1998, p.2), therefore it is possible that for left handers, as their dominant hand is being controlled by the right hemisphere, the right hemisphere may be responsible for speech control and other language functions instead of the left hemisphere.