UC San Diego

The fast pace and relative ease at which individuals with typical language acquire and use words belie the complexity and vulnerability of lexical representation development (i.e., word learning) and lexical-semantic processing. Lexical-semantic processing impairments are common in both developmental and acquired communication disorders and, even in those without such disorders, various factors can influence the abstraction, encoding, and access of lexical information. Understanding the factors that influence lexical representation development and lexical-semantic processing and how these processes might be altered in individuals with communication disorders is crucial for advancing research and supporting clinical populations.

This dissertation presents three studies that integrate behavioral and neural approaches to investigate lexical representation development and lexical-semantic processing in individuals with and without language-based communication disorders. Chapter 2 explores how deducing a novel noun or verb’s meaning from an incidental context influences later recognition of the word form in adults with typical language, revealing neural differences in encoding and accessing lexical information based on word class even when behavioral differences are absent. Chapter 3 uses a priming paradigm and event-related potentials (ERPs) to examine how the time course of an implicit mechanism underlying lexical and semantic processing, automatic spreading activation, differs between people with post-stroke aphasia (PWA) and neurologically unimpaired older adults. Chapter 4 applies a similar approach to children with developmental language disorder (DLD), investigating the potential link between the time course of spreading activation and (lexical-)semantic abilities in children with DLD and children with typical language development. Chapters 3 and 4 reveal atypical time courses of spreading activation in PWA and children with DLD, with PWA showing abnormally slow activation decay and children with DLD exhibiting atypically rapid activation decay. These chapters also show that PWA additionally struggle to integrate implicitly and explicitly processed information, and children with DLD display broader semantic processing impairments beyond lexical-semantic difficulties.

Altogether, these findings highlight how both lexical features and neurological differences affect lexical representation development and lexical-semantic processing, and—critically—exemplify the importance of considering underlying, implicit processes. They further suggest that interventions that target both the brain and behavior will lead to the greatest gains.