Links between Word Retrieval and Verbal Short-Term Memory Impairments in Aphasia

East Carolina University, Greenville NC

Investigators

Abstract

Project Summary/Abstract Effective assessment and treatment of aphasia require specific and sensitive diagnosis of the linguistic level(s) of impairment (e.g., semantic, phonologic, etc.). Recent work in aphasiology argues that language production and comprehension impairments are affected by breakdowns of shared underlying processes. These processes facilitate access to and the temporary maintenance of linguistic elements needed to produce and comprehend language. One such process is verbal short-term memory (STM), or the temporary, limited- capacity storage mechanism through which linguistic information is briefly retained. When verbal STM is impaired, access to and temporary storage of linguistic elements is compromised, leading to breakdowns in language production (i.e., expressive language) and comprehension (i.e., receptive language). Verbal STM is typically measured with an immediate serial recall span task: individuals listen to a list of numbers or words and repeat them immediately after the list ends. People with aphasia demonstrate repetition span performance below that of neurologically healthy individuals, and thus demonstrate reduced verbal STM capacity. Additionally, recent research demonstrates that individuals with aphasia whose receptive language is impaired at the semantic level show a different pattern of breakdown in serial recall tasks than individuals whose receptive language is impaired at the phonologic level. Individuals with stronger receptive semantics tend to be more accurate on items at the beginning of the list (primacy), while individuals with stronger receptive phonology tend to be more accurate on items at the end of the list (recency). Additionally, individuals with stronger receptive semantics are more accurate at recalling high imageability words (i.e., words that are easy to depict, such as ?dog?) than low imageability words (such as ?truth?), while individuals with stronger receptive phonology do not show this bias. The first aim of this research is to investigate the relationship between word retrieval impairment profiles in aphasia (greater semantic versus greater phonologic impairment) and imageabilty bias in traditional verbal STM recall tasks. The second aim is to investigate the relationship between word retrieval impairment and serial position effects in a novel verbal STM task designed to assess expressive serial recall of picture names. This novel verbal STM task is consistent with the linguistic activation requirements of word retrieval, during which activation of semantic knowledge precedes phonologic activation. Theoretically, this study will help determine the relationship between processes driving verbal STM and word retrieval. Clinically, the results of this study will inform assessment of aphasia by helping to develop a systematic way to identify the linguistic level(s) that are impaired. Additionally, if this study demonstrates that verbal STM performance is intrinsically tied to word retrieval breakdown, it will help to inform the development of treatments for aphasia that are efficient and targeted at the appropriate level(s) of linguistic impairment.