Date of Award

5-2004

Level of Access

Campus-Only Thesis

Degree Name

Master of Arts (MA)

Department

Communication Sciences and Disorders

Advisor

Nancy E. Hall

Second Committee Member

Susan Lambrecht-Smith

Third Committee Member

Alan Cobo-Lewis

Abstract

Early word comprehension and lexical development do not appear to follow directly from the sophisticated auditory abilities demonstrated by young children in their first year of life. Instead, children attend to the more global characteristics of the auditory signal and their vocabulatries consist of words that are phonectically distinct. Once their lexicons increase in size so that there is substantial phonetic overlap between words, children redirect their attention to the linear, position-specific information of the acoustic signal. Recent research in the areas of word recognition and lexical acquisition has led to the development of the term phonological neighborhoods. A neighborhood for a word includes all words that differ from the target word by only an addition, substitution or deletion of a phoneme. These neighborhoods are labeled according to their relative density: words in sparse neighborhoods have few neighbors wereas words in dense neighborhoods have many similar sounding words. Research on the application of this concept to young children's lexical development in terms of their perceptual abilities demonstrates that children initially develop sparse neighborhoods until their more mature processing strategies allow for the development of dense neighborhoods. It has been hypothesized that this reorganization occurs around the age of two, when children are experiencing a rapid growth in the size of their vocabularies. This study examined lexical development in terms of neighborhood density in four toddlers between the ages of 18 and 30 months. Longitudinal data on their productive vocabularies was collected over a 10-month period through the use of a parental checklist (McArthur Communicative Development Inventory). Phonological neighborhoods were constructed for each word on the checklist and each child's vocabulary growth was examined in terms of the neighborhood density of their lexicons over time. Findings indicated that the vocabularies of these four participants consisted of more words in sparse neighborhoods than dense neighborhoods and their development of dense neighborhoods increased over time. A considerable portion of their vocabularies; however, contained words with at least one phonological neighbor, suggesting that some level of detailed phonological processing was required to differentiate these similar sounding words. Additional analyses examined the composition of the participant's lexicons as a product of the maximum possible neighborhood size of a word according to the checklist. The results showed that the inherent density of a word was not a factor in the overall composition of these children's vocabularies. Slight differences relating to the inherent neighborhood density of a word were noted only in the acquisition of new words to their already existing vocabularies. Multiple variables that may account for the lack of neighborhood density influence in these four children are explored along with the capability of applying the neighborhood analysis to a parental checklist of lexical development.

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