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Thesis
Vocabulary breadth and depth in adults with developmental language disorder
University of Iowa
Master of Arts (MA), University of Iowa
Spring 2026
DOI: 10.25820/etd.008475
Abstract
Developmental Language Disorder (DLD) affects approximately 7–11% of children and often persists into adulthood, contributing to long-term challenges in education, employment, and health. Although vocabulary difficulties are well documented in children with DLD, less is known about how these challenges present in adulthood.
The current study investigates vocabulary knowledge in adults with DLD across two dimensions: vocabulary breadth, defined as the number of words for which an individual can retrieve a meaning, and vocabulary depth, defined as the quality of semantic knowledge for known words. Vocabulary breadth was assessed using the standardized Peabody Picture Vocabulary Test–Fifth Edition (PPVT-5). Vocabulary depth was evaluated using a novel scoring system applied to a well-established definition task, the Vocabulary subtest of the WASI-II. Linear regression analyses were conducted to examine group differences between adults with DLD and peers with typical language (TL).
Results indicated that adults with DLD (n = 38) scored significantly lower than their peers with TL (n = 58) on both measures of vocabulary breadth and depth. Additionally, the vocabulary breadth measure derived from the PPVT-5 yielded a numerically larger effect size compared to the breadth-related outcomes from the WASI-II Vocabulary task. These findings provide insight into the long-term development of vocabulary skills in adults with DLD and underscore the importance of assessing both vocabulary breadth and depth when characterizing language profiles in adulthood.
This thesis is based on a manuscript submitted to the Journal of Speech, Language, and Hearing Research.
Details
- Title: Subtitle
- Vocabulary breadth and depth in adults with developmental language disorder
- Creators
- Tingting Wang
- Contributors
- Kristi Hendrickson (Advisor)Philip Combiths (Committee Member)Elizabeth Walker (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Arts (MA), University of Iowa
- Degree in
- Speech Pathology and Audiology
- Date degree season
- Spring 2026
- DOI
- 10.25820/etd.008475
- Publisher
- University of Iowa
- Number of pages
- vii, 27 pages
- Copyright
- Copyright 2026 Tingting Wang
- Language
- English
- Date submitted
- 04/06/2026
- Description illustrations
- Illustrations, graphs, tables
- Description bibliographic
- Includes bibliographical references (pages 20-24).
- Public Abstract (ETD)
Developmental Language Disorder (DLD) affects about 7–11% of children and often continues into adulthood. People with DLD may face long-term challenges in school, work, and daily life. While researchers know a lot about vocabulary difficulties in children with DLD, we know much less about how these difficulties look in adults. This study helps fill that gap.
We examined vocabulary knowledge in adults with DLD in two domains. First, we looked at vocabulary breadth, or how many words a person understands. Second, we looked at vocabulary depth, or how well a person understands the meanings of words. We compared 38 adults with DLD to 58 adults with typical language skills using standardized tests and a structured definition task.
Our results showed that adults with DLD had weaker vocabulary skills in both domains. They knew fewer words overall and had less detailed understanding of the words they did know. We also found that both the picture-based test and the definition task were sensitive to differences in vocabulary skills. These findings show that vocabulary challenges do not disappear in adulthood for people with DLD. Understanding both how many words someone knows and how well they know them can give a clearer picture of their language abilities. This information can help guide assessment and support for adults with DLD in education, the workplace, and everyday communication.
This thesis is based on a manuscript submitted to the Journal of Speech, Language, and Hearing Research.
- Academic Unit
- Communication Sciences and Disorders
- Record Identifier
- 9985177176202771
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