Focusing : a dual systems account for the apparent hemispheric lateralisation of language
A model termed the 'Focusing Hypothesis' is presented. It is proposed that language processing is shared by an analytic and a holistic system, according to a task specific balance of demand and efficiency. The analytic system could function alone, but it is more economical, in normal communication, for holistic processing to operate up to clausal level and analysis to deal with the evaluation of propositions. The severe limitations on the abilities of the holistic system originate from its use of formulae to recognise familiar words in familiar structures. Where problems arise, the analytic system 'trouble-shoots', by focusing attention onto the language, at the expense of propositional focus. The relative involvement of the two systems is variable, according to the strategy selected from a task specific strategy option range; the strategy option range and preferences within it are built up as a response to the environmental requirements placed on the individual. Apparent evidence for left hemisphere lateralised language is re-examined in the light of this hypothesis, which proposes that the test environment of most psycholinguistic and clinical assessments induces a language-focusing strategy and thus deactivates the right hemisphere (holistic) mechanisms. It is predicted that careful modifications to the methods of test administration could reveal right hemisphere activity by permitting it to occur. Support for the hypothesis is drawn from the literature relating to neurophysiological (dynamic) studies and from the reported symptoms of left and right hemisphere damaged patients. Accounts of polyglot (bilingual) acquisition and storage and of differential language loss in polyglot aphasia are also examined. Output processing is examined with reference to one specific hypothesis (Pawley & Syder 1983) which closely aligns with the one for input presented by the Focusing Hypothesis. Two experiments attempt to examine contrasts in strategy as a function of age (Experiment I) and stimulus type (Experiment II). Neither displays strong patterns of the kind predicted to be associated with contrasts in hemispheric superiority according to strategy choice, and it is suggested that, despite the attempt, the experimental designs failed to enable consistent access to the proposition-focused strategies held to be operational in normal communication, that is, those involving holistic processing.