Language Processing and Production Essay

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. Additional research looking at right hemisphere lesions has demonstrated that the right hemisphere is responsible for some linguistical functions: finding that patients with such lesions may be ‘impaired relative to normal controls on certain tests of language’ (Corballis, C. M. 1983, p. 33). One study by Lesser (1974) reported such an impairment ‘on a semantic test involving comprehension of spoken words but not on a phonological or syntactic test’ (Corballis, C. M. 1983, p. 33), suggesting a small role for the right hemisphere in language processing. Kinsbourne and McMurray carried out valuable research using healthy participants, using a procedure similar to the current study (cited in Kalat, 2004, pg. 427). They asked participants to tap with a pencil on a piece of paper as many times as they could in one minute, first with their right hand then with their left, then asked them to do the same again whilst talking, they found that ‘for most right-handers, talking decreases the tapping rate with the right hand more than with the left hand’. This further supports left hemispheric dominance for language, as well as supporting the current study’s methodology and informing its hypothesis. As has been demonstrated most research supports left hemispheric dominance of language functions, but also links hemispheric specialisation with other factors and accepts that the right hemisphere holds some language comprehension control. This experiment looks for further supportive evidence and also briefly looks at handedness as a possible affecting factor. The study uses a finger tapping and language processing task, with the notion that the speed at which keys are pressed will be relatively similar with both hands. If however, if it is the case that language is more associated with the left hemisphere, then on average when processing language, the speed of the right hand will be slower than the left hand, presumably because the left hemisphere then has to do two tasks at once (right hand finger tapping and language processing). This is only the case however if all participants in the experiment have left hemisphere dominance for language, and is thus the reason we have recorded the handedness of our participants. As a result of previous studies and research the hypothesis for this experiment is: there will be differences in the number of taps made from each of the two hands when language is or isn’t being processed. Method Design The experiment used a fully repeated measures within-subjects design: all participants took part in all conditions. There was one independent variable, consisting of four different levels: left hand, talking, no talking and right hand talking, no talking. The dependent variable was the number of key presses made within the time limit of 30 seconds per trial.