Phonological and Semantic Working Memory and Discourse Coherence in Fluent Aphasia

Abstract

Studies have found that people with aphasia demonstrate reduced nonverbal and verbal short-term memory (STM) and working memory (WM) and discourse measures related to topic maintenance such as global and local coherence. Research also suggests that STM capacity and WM abilities may influence discourse measures such as global and local coherence in people with aphasia and acquired brain injuries (ABI). The purpose of this study was to determine how differences in the domain (nonverbal or verbal) or linguistic level (phonological or semantic) of information held and manipulated in STM may influence global and local coherence in people with mild-moderate fluent aphasia. A forward Corsi block and subtests from the Temple University Assessment of Language and Verbal Short-term Memory in Aphasia (TALSA) were used to assess nonverbal, phonological, and semantic WM. 13 participants with mild-moderate fluent aphasia and 4 neurotypical adults completed the forward Corsi block and phonological and semantic WM subtests from the TALSA. These included various probe spans and pointing tasks (rhyming and synonymy triplets subtests), which required the participant to maintain a number of words and make different semantic and phonological decisions about these words (e.g. making judgements related to the rhyme (phonological) or the categorization (semantic) of the words). Pointing tasks (rhyming and synonymy triplets) involved participants pointing to words on a screen that shared a similar phonological (rhyme of the words) or semantic (meaning of the word) relationship in a high and low WM condition. All participants with aphasia and neurotypical adults completed 10 discourse samples from the Nicholas and Brookshire narratives. Global and local coherence were assessed by rating each C-unit from participants’ discourse samples on a 1-5-point global and local coherence rating scale. This study determined if there was a relationship between the nonverbal, phonological, and semantic WM tasks and global and local coherence in the people with mild-moderate fluent aphasia. This study found that only the synonymy triplets change score (difference between the low WM condition and the high WM conditions), a semantic WM task, from the TALSA demonstrated a trend towards significance with local coherence in the participants with aphasia group. Additionally, a similar relationship was found when the same correlations were run on a group that combined the neurotypical adults and participants with aphasia group. Similarly, this study found that only the synonymy triplets change score had a significant correlation with local coherence in the combined group. None of the other WM tasks were significantly correlated with global and local coherence. Based on these results, this study provides some evidence that the integrity of the cognitive resources used for the maintenance and manipulation of semantic information held in verbal STM may be important for maintaining the topic or semantic coherence between adjacent utterances (measured by local coherence) in participants with mild-moderate fluent aphasia and neurotypical adults. More research is needed to determine if this relationship exists in other populations with aphasia and in an independent sample of neurotypical adults.