The relationships between anomia and short-term memory deficits

Anomia is the most common symptom of language dysfunction occurring in aphasia. Moreover, verbal short-term memory (STM) impairments are a frequent characteristic of aphasic syndromes. However, the nature of these deficits and their relationships to language production impairments in these patients are still debated. Recent STM models have been proposed incorporating relationships between language representations and STM, including distinct capacities for temporary storage of phonological and lexical-semantic information (N. Martin & Saffran, 1992; R. Martin, Lesch, & Bartha, 1999). This study explores the relationships between anomia and STM deficits. We assume that a naming impairment may be related to either a phonological STM impairment with preserved lexical-semantic STM or to an impaired lexical-semantic STM with preserved phonological STM. We tested these predictions in two aphasic patients, BN and TM. Phonological STM was assessed using a rhyme-probe task (R. Martin et al., 1999) and a lexical-decision task, each target word being preceded by a phonologically related prime word. Lexical-semantic STM was assessed by a category-probe task and a lexical-decision task with semantically related primes. BN was impaired on the rhyme-probe task and presented a reversed phonological priming effect, suggesting phonological STM impairment. However, she presented normal performance on the category-probe task and a normal semantic priming effect. By contrast, TM performed normally on the rhyme-probe and phonological lexical-decision tasks but was impaired on the category-probe task and presented no semantic priming effect, indicating lexical-semantic STM impairment. Moreover, both patients’ word retrieval capacity, as assessed with a picture naming task, was impaired. BN produced phonological paraphasias, repetitive self-corrections and presented an increased length effect. We assume that BN’s errors and effects may be related to her phonological STM deficit. TM instead produced semantic paraphasias, omissions and circumlocutions and presented an increased frequency effect. These errors and effects may be related to his lexical-semantic STM deficit. Results show a double dissociation between phonological and lexical-semantic STM deficits. Furthermore, the patients’ naming patterns seem to indicate that their naming impairment may be related to a selective STM deficit. The results are discussed within the STM framework of N. Martin and Saffran (1992). Martin, N., & Saffran, E. (1992). A computational account of deep dysphasia: evidence from a single case study. Brain and Language, 43(1), 240-274. Martin, R. C., Lesch, M. F., & Bartha, M. C. (1999). Independence of input and output phonology in word processing and short-term memory. Journal of Memory and Language, 41(1), 3-29