Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Health and Rehabilitation Sciences

Supervisor

Archibald, Lisa M. D.

Abstract

The language system is highly flexible and draws on distinct but interconnected cognitive mechanisms, including verbal working memory and long-term linguistic knowledge. Verbal working memory is the ability to manipulate verbal information in mind. Long-term linguistic knowledge refers to our knowledge of the language (i.e., phonology, semantics, syntax), stored in long-term memory. The close interaction between verbal working memory and linguistic knowledge highlights a pressing need to investigate the construct of verbal working memory, its separability and its relationship with linguistic knowledge. To understand the way working memory influences and interacts with language abilities in children and adults, I ask the following questions: Are verbal working memory and language separable constructs? And, does verbal working memory operate within a dynamic network of cognitive systems including the language network? In Chapter 2, I examined whether working memory and linguistic abilities could be teased apart using the same language task, namely a modified Token Test. Indeed, factors related to working memory and linguistic abilities explained performance on our modified Token Test and were differentially related to other language measures. Despite evidence of separability, it must be acknowledged that verbal working memory and language processing are highly intertwined. Chapters 3 and 4 investigated this interrelationship in detail. Specifically, I used experimental tasks to delineate the involvement of phonological and semantic representations in the maintenance of verbal items (words, sentences) in working memory. In Chapter 3, I used a novel word recognition paradigm and found separable phonological and semantic effects on immediate memory, with semantic processing supporting long-term retention. These findings confirmed that both phonological and semantic information were readily activated and accessed when a word is encountered and processed. Chapter 4 further evaluated the interplay between different cognitive processes underlying verbal working memory in the context of sentence recall. Similarly, results supported the idea that multiple representations influence performance, but their contributions differ. Semantic processing was beneficial for both immediate and long-term memory whereas phonological processing had more immediate benefits. Finally, in the concluding chapter, I discuss the importance of these results for models of verbal short-term memory and highlight some potential implications for clinical practice.

Summary for Lay Audience

Language processing is influenced by many cognitive factors including verbal working memory, which is the ability to hold and process some aspect of language in mind, and linguistic knowledge, which is our knowledge about the rules of language. Think about what it means to hold a word or sentence in mind. This means not only knowing the phonological word form (or speech sounds that make up the word) but also having rich linguistic knowledge such as semantic information (or meaning-based information) associated with it. It would be difficult to fully understand what factors are impacting language performance without considering the role of both working memory and linguistic knowledge. In this thesis, I aim to investigate the construct of verbal working memory, its separability and its relationship with long-term linguistic knowledge. Chapter 2 evaluated potential working memory and language demands of different language tools in a group of children. Although children employ both working memory skills and linguistic knowledge during language-based tasks, I found that differential performance across language measures could be revealing of greater reliance on working memory or language skills to support performance. Chapters 3 and 4 examined the relationship between verbal working memory and long-term language knowledge by manipulating linguistic variables specifically. In particular, I focused on how phonological and semantic knowledge contribute to the maintenance of verbal items (words, sentences) in working memory. In Chapter 3, I examined the involvement of phonological and semantic information at the word-level and found that phonological and semantic information were all activated when a word was encountered and processed, with access to semantic knowledge benefiting long-term retention. In Chapter 4, I built on these findings to investigate how phonological, semantic, and attentional mechanisms are contributing to language performance at the sentence-level. Similarly, results supported the idea that sentence recall taps phonological, semantic, and attentional processes interactively but their contributions for immediate and long-term recall differed. Overall, results from this dissertation will help us understand the relationship among working memory processes, linguistic knowledge, and language functioning from a theoretical and clinical perspective.

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