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Right Hemispheric Use of Image Processing During Language Comprehension

Researcher Jenine Wenn

Supervisors Dr Jeffrey Coney & Dr Bethanie Gouldthorp

Date: 10 June, 2010

Rationale and Hypothesis:

Recent research suggests that whilst both hemispheres process information at the word-level (i.e. the basic lexical association between single words within text), it may be the right hemisphere that is largely contributing to the message-level (i.e. combining syntactic, semantic and pragmatic information from text) (Gouldthorp, 2010; Gouldthorp & Coney, 2009). The right hemisphere’s contribution to the message-level may be in the application of mental imagery to pragmatic information. Language comprehension may require the construction of a perceptual simulation of the meaning of the text. The perceptual simulation, derived from background knowledge and perceptual experiences, then becomes a reader’s situation model. Zwaan and Radvansky (1998) maintain that language can be viewed as a set of instructions that construct a mental representation of a described situation. Based on the findings from previous research, the present study investigated the notion that the right hemisphere may be using a language processing mechanism that relies on an image-based representation, which may then support the left hemisphere in comprehending a described situation. It was hypothesised that the facilitation from text-based images would be greater for the right hemisphere than the left hemisphere, given that the right hemisphere has been shown to be superior at processing visuo-spatial information (e.g. Kensigner & Choi, 2009). Two possible confounds were taken into consideration: individual differences in the vividness of visual imagery and individual differences in the enjoyment of reading. It was hypothesized that there would be significantly greater facilitation for vivid imagers/high reading enjoyment, than non-vivid imagers/low reading enjoyment and a greater difference in facilitation for the right hemisphere than the left hemisphere.

Method/design:

The hypotheses were tested by presenting purely linguistic information from which meaning could only be derived if an image was produced by means of the situational rather than propositional model. The propositional information given in each sentence, when imaginably integrated, then provided meaning. A set of verbal instructions were used to elicit a particular mental image. For example, “Draw a wavy vertical line. Then directly at the top of the line, draw a small vertical oval. At the top of the oval, extending upwards, draw a very small red letter Y”. The lateralized target word representing the picture would then be “snake”. Great effort was taken to ensure the target words were not explicitly referred to in the passages. Targets were either ‘related’, where the target matched the text-based image, or ‘unrelated’, whereby the target did not represent the text-based image. Stimulus construction consisted of 160 targets. Two separate stimulus set files were constructed from the 160 passages, so that each stimuli set would be shown equally for each condition to each visual field.

Main Results:

Participants’ reaction times were significantly faster in the related condition, with both hemispheres benefiting more from the facilitation produced in the related, than the unrelated, condition. This finding clearly supported the effectiveness of the design. However, the right hemisphere did not benefit significantly more from facilitation than the left hemisphere. Interestingly, both hemispheres equally benefited from message-level facilitation.

Facilitation for related targets was not significantly greater when presented to the right hemisphere than the left hemisphere when controlling for individual differences in the vividness of visual imagery or reading enjoyment. However, the difference between lexical decision latencies overall was significantly greater for high, compared to low, visual imagers. Vivid imagers were superior to non-vivid imagers in producing a mental representation from the propositional information provided.

Conclusions:

On the whole the findings from this study are inconsistent with the notion that the right hemisphere is primarily using an image based situation-model processing method to support the left hemisphere in message-level comprehension. Not only did facilitation of the related targets occur regardless of which visual field it was presented to, the amount of facilitation did not differ significantly between them. The strength of this finding was supported by the large effects observed between the hemispheres and the priming passage-target conditions. A strategic process may have been employed, whereby the participants utilized the auditory presentation to carry out a pre-response check on the validity of their lexical decision. The participants may have used a lexical checking strategy, whereby priming for target words only became obvious when the participants were aware of the relation between the passage-target. This strategy would have produced facilitation for the related targets and inhibition for the unrelated targets, which may account for why facilitation on the RH was not greater than LH facilitation.

To our knowledge, this is the first study of its kind to attempt to clarify the RH’s contribution to message-level processing through situation model construction using a cross-modal lexical decision task without utilizing semantic associations. As it is an exploratory experimental design it should be emphasized that these results are preliminary and that future refinement of the procedure (i.e. a neutral condition) is required to resolve many of the non-significant findings. In this light, the task confronting those interested in RH use of situation modeling for message-level sentence comprehension is either to: (a) demonstrate the relevance of lexical decision tasks for situation-model processing, or; (b) develop a different task that more faithfully reflects the processes involved in situation model construction during message-level processing. The challenge for psycholinguistic theories for RH use of message-level processing in the application of mental imagery to pragmatic information, if this speculation is pointing in the right direction, is to find tasks or techniques (e.g. neuroimaging) that can target the areas selectively. Further investigation is imperative to determine the true nature of message-level processing in the RH in order to aid rehabilitation and reading programs.