Jargon Busting: The cognitive mechanisms underpinning nonword errors and perseveration in Jargon aphasia

Abstract

Jargon aphasia is a term used to refer to an acquired language disorder after stroke where high proportions of nonword error are produced in spoken output, reducing the intelligibility of speech and limiting communication effectiveness. A number of theoretical hypotheses have been proposed to explain nonword production in Jargon aphasia; the major hypotheses implicate lexical and phonological error sources. However, there exist few experimental studies testing these accounts. This thesis presents three studies which explore contributions from lexical and phonological processes to nonword error and Jargon production, drawing on data from twenty people with Jargon-like production deficits post-stroke. The first experimental chapter explores nonword error patterns in Jargon aphasia across word production tasks with different lexical-phonological demands – reading, repetition, and naming, to examine whether phonological and/or lexical error sources can account for the observed patterns. The second experimental chapter analyses whether poor activation of phonological information from lexical selection mechanisms can account for error patterns in Jargon aphasia. To test this target word sets with different lexical availability, indexed by lexical-semantic properties associated with lexical retrieval, were used in tasks of single word repetition and reading. Crucially, these word sets were matched for their phonological processing demands. The third experimental chapter analyses whether inhibitory deficits contribute to the Jargon aphasia profile by manipulating the inter-stimulus time and tasks demands in between target words in reading aloud, to target the post-production time window associated with inhibitory processing after word production. Group and case-series analyses were implemented in all three experimental studies. Results demonstrate that Jargon quantity is increased in tasks which have greater phonological demands, indicating a significant contribution from phonological processing to Jargon nonword error production. The success of phonological production was not consistently influenced by lexical availability, suggesting that greater amounts of lexical activation do not better inform phonological processing and implies that the phonological system is not able to utilise lexical-semantic activation effectively. The third study indicated that inhibitory processes could be manipulated in some people with Jargon aphasia, suggesting that problems inhibiting phonological material postproduction contribute to the Jargon presentation for some individuals; however this was not a universally contributing factor in Jargon production. Overall, results suggest that people with Jargon aphasia consistently present with phonological impairments; however, additional impairments in lexical-semantics and inhibitory processing may also contribute to the Jargon presentation. Results suggest that, for some people with Jargon aphasia, activation (of lexical-semantics) and inhibition processes can be manipulated to minimise the quantity and severity of Jargon production. However, many participants demonstrated stable and consistent patterns of production despite the experimental manipulations, suggesting severe phonological processing impairment which is resistant to lexical-semantic and inhibitory variables.