The aim of this research is to translate a theory of the cognitive relationship between verbal short-term memory (STM) and word processing impairments in aphasia to treatment approaches for language impairment in aphasia. Aphasia is typically viewed as a language disorder and yet it is invariably accompanied by a reduction in verbal STM capacity. Based on our research of word processing and verbal STM impairments in aphasia, we have proposed that the co-occurrence of these impairments is due to a disruption of cognitive processes that support both abilities: maintenance of activated semantic and phonological representations of words, hereafter the 'activation-maintenance hypothesis' (Martin and Saffran, 1997~ Martin, 2008). We will test this hypothesis in the context of a treatment approach that aims to improve word processing and verbal STM abilities. Recently, the importance of treatment research as a critical testing ground for theories of language processing has been emphasized (Nickels et al., 2010). Although we have demonstrated associations between impairments of word processing and reduced verbal STM capacity, the activation-maintenance hypothesis presumes a causal association between maintenance of activated semantic and phonological representations and the integrity of both word processing and verbal STM. Direct treatment to improve the ability to maintain activation of word representations will serve as a stronger test of this hypothesis. First, we will establish empirical support for the hypothesis that impairment to short-term maintenance of activated semantic and phonological representations of words impairs language and verbal STM abilities in aphasia and that direct treatment of this deficit will improve both abilities (Specific Aim 1). This support will be obtaind in a short-term facilitation study and two treatment studies that use repetition of verbal stimuli under conditions that increase memory load. We also predict that increasing memory load in language training tasks will improve performance on the training task (repetition) as well as other language tasks that share processing pathways with repetition. Second, we will compare effects of this treatment under two administration conditions, high and low intensity (Specific aim 2). Recent evidence suggests that language treatments are more effective when administered on more intense schedules (Bhogal et al., 2003), but more evidence is needed from studies that directly compare high and low intensity schedules of treatment. Finally, we will investigate neural regions associated with semantic STM and phonological STM using voxel-based lesion- symptom mapping (Bates et al., 2003) (Specific Aim 3). Following recent functional MRI studies (e.g., Shivde and Thompson-Schill, 2004), we predict that reduced semantic STM will be associated with inferior frontal parietal lesions and reduced phonological STM with lesions in the left superior parietal region. This project represents a unique attempt to apply more recent processing theories of aphasia to treatment of the disorder. The outcomes will have important implications for aphasia rehabilitation research.
Approximately one million people in the United States have aphasia, a language impairment most often resulting from a stroke (National Aphasia Association, www.aphasia.org). Recent research has demonstrated that impairments to other cognitive abilities such as verbal short-term memory nearly always accompany the language impairment in aphasia. This indicates a need to develop treatment approaches that target both language and nonlinguistic cognitive abilities that support language function.
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