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A beautiful day in the neighborhood: The influence of neighborhood density on speech production

ProQuest Dissertations and Theses, 2009
Dissertation
Author: Skott Elliot Freedman
Abstract:
The goal of the current work was to investigate the influence of neighborhood density (ND) on speech production. ND is an index of phonological similarity and refers to the number of meaningful words (neighbors) present in a language that differ only by adding, deleting, or substituting a phoneme in any word position (Vitevitch & Luce, 1998, 1999). Prior studies of ND have yielded conflicting findings for production, reporting both inhibitory and facilitory effects of ND (Heisler, 2004; Vitevitch, 2002). In order to discern whether words may act more as competitors or facilitators (or potentially neither) during speech production, three experiments were conducted with 39 preschoolers and 46 adults with typical development: Experiment 1 explored influences of ND during children's picture-naming, Experiment 2 considered effects of ND on adult word repetition, and Experiment 3 discerned the influence of ND during word learning in both age groups. Analyses of production included segmental and whole-word level errors, as well as the lexical nature of production errors. Results revealed varying effects of ND depending upon the task and group. Specifically, children's naming was facilitated by ND at the semantic level, yet unaffected by ND at the phonological level. Adult word repetition was facilitated by ND in terms of repetition accuracy and the nature of erred repetitions. Finally, an inhibitory effect of ND was found during word learning by children, while adults were seemingly unaffected by the ND manipulation during word learning. Taken together, the results suggest that words do not simply act as competitors or facilitators during speech production; rather, their interactive nature likely depends on the elements of a task and the developing status of the lexicon. Neighbors of a word appeared to generally act as facilitators until a threat was posed, such as when acquiring novel words that were similar in phonological composition to existing words in the lexicon. This research indicates that incorporating ND into experimental or treatment paradigms should be used with caution and should be based on the demands of a task as well as the participants involved.

TABLE OF CONTENTS

Signature Page ............................................................................................................... iii Dedication ...................................................................................................................... iv Epigraph ......................................................................................................................... v Table of Contents .......................................................................................................... vi List of Abbreviations ...................................................................................................... x List of Figures ................................................................................................................ xi List of Tables ................................................................................................................ xii Acknowledgments ....................................................................................................... xiii Curriculum Vitae ......................................................................................................... xvi Abstract ........................................................................................................................ xxi

Chapter 1: Background and literature review ................................................................. 1 Introduction ........................................................................................................ 2 1.0 ....................................................................................................................... 4 1.0.1 ........................................................................................................ 4 1.0.2 ........................................................................................................ 6 1.0.3 ........................................................................................................ 8 1.0.4 ...................................................................................................... 14 1.1 ..................................................................................................................... 15 1.1.1 ...................................................................................................... 16 1.1.2 ...................................................................................................... 18 1.1.3 ...................................................................................................... 20 1.1.4 ...................................................................................................... 21 1.1.5 ...................................................................................................... 23 1.1.6 ...................................................................................................... 24 1.1.7 ...................................................................................................... 26 1.1.8 ...................................................................................................... 27 1.2 ..................................................................................................................... 30 1.2.1 ...................................................................................................... 30 1.2.2 ...................................................................................................... 30 1.2.3 ...................................................................................................... 31 1.2.4 ...................................................................................................... 33

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Chapter 2: Children’s naming as a function of neighborhood density ......................... 36 2.0 ..................................................................................................................... 37 2.0.1 ...................................................................................................... 37 2.0.2 ...................................................................................................... 38 2.0.3 ...................................................................................................... 40 2.0.4 ...................................................................................................... 42 2.1 ..................................................................................................................... 43 2.1.1 ...................................................................................................... 43 2.1.2 ...................................................................................................... 46 2.1.3 ...................................................................................................... 49 2.1.4 ...................................................................................................... 49 2.1.5 ...................................................................................................... 50 2.2 ..................................................................................................................... 53 2.2.1 ...................................................................................................... 54 2.2.2 ...................................................................................................... 54 2.2.3 ...................................................................................................... 55 2.2.4 ...................................................................................................... 55 2.2.5 ...................................................................................................... 56 2.3 ..................................................................................................................... 56 2.3.1 ...................................................................................................... 57 2.3.2 ...................................................................................................... 58 2.3.3 ...................................................................................................... 60 2.3.4 ...................................................................................................... 61 2.3.5 ...................................................................................................... 62 2.3.6 ...................................................................................................... 63

Chapter 3: Effects of neighborhood density on adult word repetition ......................... 64 3.0 ..................................................................................................................... 65 3.0.1 ...................................................................................................... 65 3.0.2 ...................................................................................................... 66 3.0.3 ...................................................................................................... 67 3.0.4 ...................................................................................................... 68 3.0.5 ...................................................................................................... 71 3.1 ..................................................................................................................... 72 3.1.1 ...................................................................................................... 72 3.1.2 ...................................................................................................... 72 3.1.3 ...................................................................................................... 75 3.1.4 ...................................................................................................... 77 3.1.5 ...................................................................................................... 77 3.2 ..................................................................................................................... 78 3.2.1 ...................................................................................................... 79 3.2.2 ...................................................................................................... 79 3.2.3 ...................................................................................................... 80 3.2.4 ...................................................................................................... 82 3.3 ..................................................................................................................... 82 vii

3.3.1 ...................................................................................................... 82 3.3.2 ...................................................................................................... 84 3.3.3 ...................................................................................................... 86 3.3.4 ...................................................................................................... 87 3.3.5 ...................................................................................................... 88 3.3.6 ...................................................................................................... 88 3.3.7 ...................................................................................................... 89

Chapter 4: Influence of neighborhood density on word learning ................................. 90 4.0 ..................................................................................................................... 91 4.0.1 ...................................................................................................... 91 4.0.2 ...................................................................................................... 92 4.0.3 ...................................................................................................... 94 4.0.4 ...................................................................................................... 96 4.1 ..................................................................................................................... 99 4.1.1 ...................................................................................................... 99 4.1.2 .................................................................................................... 100 4.1.3 .................................................................................................... 105 4.1.4 .................................................................................................... 106 4.1.5 .................................................................................................... 107 4.2 ................................................................................................................... 109 4.2.1 .................................................................................................... 110 4.2.2 .................................................................................................... 112 4.2.3 .................................................................................................... 115 4.2.4 .................................................................................................... 116 4.2.5 .................................................................................................... 116 4.3 ................................................................................................................... 117 4.3.1 .................................................................................................... 118 4.3.2 .................................................................................................... 119 4.3.3 .................................................................................................... 120 4.3.4 .................................................................................................... 121 4.3.5 .................................................................................................... 123 4.3.6 .................................................................................................... 124 4.3.7 .................................................................................................... 125 4.3.8 .................................................................................................... 126 4.3.9 .................................................................................................... 126 4.3.10 .................................................................................................. 127

Chapter 5: Discussion ................................................................................................. 129 5.0 ................................................................................................................... 130 5.0.1 .................................................................................................... 131 5.1 ................................................................................................................... 133 5.1.1 .................................................................................................... 134 5.1.2 .................................................................................................... 136 5.1.3 .................................................................................................... 137 viii

5.2 ................................................................................................................... 139 5.2.1 .................................................................................................... 139 5.3 ................................................................................................................... 141 5.3.1 .................................................................................................... 141 5.3.2 .................................................................................................... 142 5.4 ................................................................................................................... 142 5.4.1 .................................................................................................... 142 5.4.2 .................................................................................................... 143 5.4.3 .................................................................................................... 145

Appendix .................................................................................................................... 146

References .................................................................................................................. 161

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LIST OF ABBREVIATIONS

ND ................................................................................................. neighborhood density PP ................................................................................................. phonotactic probability WFI ........................................................................................... word-finding impairment PPVT .......................................................................... Peabody Picture Vocabulary Test PMLU .................................................................. phonological mean length of utterance PWP ........................................................................ proportion of whole-word proximity PI ............................................................................................... phonological impairment x

LIST OF FIGURES

Figure 2.1: Mean percentage accuracy rates for children’s naming by analysis and condition ....................................................................................................................... 56

Figure 3.1: Mean percentage accuracy rates for adult word repetition by analysis and condition ....................................................................................................................... 81

Figure 3.2: Comparison of neighborhood density between targets and substitutions during adult word repetition ......................................................................................... 81

Figure 4.1: Mean binary production accuracy for nonwords at baseline by condition ..................................................................................................................... 111

Figure 4.2: Mean binary production accuracy for adult word learning by condition and time ............................................................................................................................. 112

Figure 4.3: Mean segmental production accuracy for nonwords at baseline by age and condition ..................................................................................................................... 114

Figure 4.4: Mean segmental production accuracy for word learning by age, condition, and time ...................................................................................................................... 115

Figure 4.5: Comparison of neighborhood density between targets and substitutions during word learning by age ....................................................................................... 116 xi

LIST OF TABLES

Table 1.1: Selected studies of ND by age and task ...................................................... 27

Table 2.1: Mean percentage accuracy rates and standard deviations for children’s naming by analysis and condition ................................................................................ 54

Table 3.1: Mean percentage accuracy rates and standard deviations for adult word repetition by analysis and condition ............................................................................. 79

Table 3.2: Means and standard deviations of neighborhood density for adult word repetition by response type ........................................................................................... 80

Table 4.1: Nonword stimuli by neighborhood density, condition, and semantic property ....................................................................................................................... 101

Table 4.2: Mean binary production accuracy rates and standard deviations for adult word learning by condition and point in time ............................................................ 111

Table 4.3: Mean segmental production accuracy rates and standard deviations for word learning by age, condition, and point in time .................................................... 113

Table 4.4: Means and standard deviations of neighborhood density for word learning by response type and age ............................................................................................ 116

Table 5.1: Summary of current results ....................................................................... 131 xii

ACKNOWLEDGMENTS

Fred Rogers, famous TV personality who has provided plenty of fodder for my variable of interest (neighborhood density), once said, “It always helps to have people we love beside us when we have to do difficult things in life.”. This statement could not be truer for my experience throughout graduate school. I have been educated, challenged, and stimulated more than I ever thought possible, and I would like to acknowledge all of the individuals who played a role in my journey. First and foremost, I am extremely grateful to my dissertation committee chair and advisor, Dr. Jessica Barlow, who has been a constant source of wisdom and encouragement over the years. Under Jessica’s guidance, I learned there was so much more to language than mere sounds and words, and that fine-grained differences were pools of mystery just waiting to be explored. She also helped me to realize a career path should be based on one’s own choices and not others’ expectations. In this sense I feel so fortunate to have had a mentor who has always respected and supported my interests, research ideas, and career decisions. I also would like to thank Dr. Sonja Pruitt, whose contagious enthusiasm has helped me through some of my most difficult days in graduate school. Her anecdotes and advice have been an invaluable asset to my education, and I have learned more from her (school-related and not) than she will ever know. I want to express my sincere appreciation to the other members of my dissertation committee: Dr. Eric Bakovic, Dr. Victor Ferreira, and Dr. Rachel Mayberry. They were always supportive of my research program and have provided xiii

thought-provoking, constructive comments throughout the dissertation process. It has been an honor to work with each of them. This dissertation would not have been possible without the selfless participation of so many adults, children, and their parents. I want to thank all of the participants for volunteering with absolutely no expectations in return. A special thank you goes to Liz Witztum for “rallying” the troops and calling me every other day with a different parent who was on board. I also want to thank Sarah Cercon and Stephanie Burgener for lending their voices to the project, and Adam Jacobson and Erin Brown for lending their ears for analyses. During my time at SDSU and UCSD, many individuals have shown me great kindness and provided invaluable assistance. I offer my gratitude to Dr. Beverly Wulfeck, Dr. Lew Shapiro, Dr. Jenny Hoit, Dr. Peter Torre III, Dr. Ignatius Nip, Dr. Tracy Love, and Dr. Don Robin. Their expertise and guidance will not be forgotten. I would also like to thank the past and present administrative staff of the doctoral program, Carmen Curphy and Jill Baumgartner. Their smiles and kindness were always appreciated. I have been the fortunate recipient of many funding sources over the years. My research program and studies would not have been possible without the generosity of: NIDCD 1T32 DC007361, “Neurocognitive Approaches to Communication Disorders”; the Sheila and Jeffrey Lipinsky Family Fellowship in Language and Communicative Disorders; the Kala Singh Memorial Scholarship; and the Sam Foshee Memorial Scholarship. I want to thank all of my past and present school peers for consistent good xiv

advice and laughter, and for cheering me on until the very end. A special thank you goes to Bridget Bowler, Barb Brenner, Edwin Maas, Shannon Austermann Hula, Alycia Cummings, Szilvi Mckinney, Josée Poirier, Marisa Sizemore, and Roberto Gutierrez for constant support. Additional thanks are due to the faculty in the Department of Speech-Language Pathology and Audiology at Ithaca College for first introducing me to the field of speech-language pathology 10+ years ago. I would like to thank my parents for their unconditional love and encouragement, even when I cringed every time I heard “How much longer?” They gave me a “Speak and Spell” when I was 4-years-old and thus my love for language was born. Their immeasurable emotional and financial kindness over the years has truly humbled me. I am also grateful to my brother Joshua and my sister Jamie, who have always been 150% behind me. Finally, thank you to Steve Jones, who over the past five years has shown me a friendship and love I was unaware existed. He has been my anchor throughout the dissertation process, my lighthouse. And thank you to Riley (who will never read these pages), whose constant purring presence on my lap throughout writing hundreds of pages has reminded me to relax, breathe, and once in a while just take a nap.

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CURRICULUM VITAE

Academic Appointments

January 2010 Assistant Professor, Department of Speech-Language Pathology and Audiology, Ithaca College

Education

2009 Doctor of Philosophy, Language and Communicative Disorders, San Diego State University and University of California, San Diego

2007 Master of Arts, Speech, Language, and Hearing Sciences, San Diego State University

2001 Bachelor of Science, Speech Pathology and Audiology, Ithaca College

Awards and Funding

2009 New Century Scholars Doctoral Scholarship, American Speech- Language-Hearing Association 2009 Travel Award, Graduate Student Association, San Diego State University 2009 Travel Award, American Speech-Language-Hearing Association 2009 ASHA Editor’s Award: Maas, E., Robin, D.A., Austermann Hula, S.N., Freedman, S.E., Wulf, G., Ballard, K.J., & Schmidt, R.A. (2008). Principles of motor learning in treatment of motor speech disorders. American Journal of Speech-Language Pathology, 17, 277-298. 2008-2009 Sheila and Jeff Lipinsky Family Scholarship, San Diego State University 2008 Travel Award, Graduate Student Association, San Diego State University 2008 Travel Award, College of Human and Health Services, San Diego State University 2005-2007 Predoctoral Fellowship, National Institutes of Health 2005-2006 Kala Singh Memorial Scholarship, San Diego State University 2005 Travel Award, National Institutes of Health 2004-2005 Sam Foshee Memorial Scholarship, San Diego State University

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Publications

Freedman, S.E., Maas, E., & Robin, D.A. (2008). Neurofibromatosis. In M.R. McNeil (Ed.), Clinical Management of Sensorimotor Speech Disorders (2 nd

edition). New York, NY: Thieme.

Maas, E., Freedman, S.E., & Robin, D.A. (2008). Traumatic brain injury. In M.R. McNeil (Ed.), Clinical Management of Sensorimotor Speech Disorders (2 nd

edition). New York, NY: Thieme.

Maas, E., Robin, D.A., Austermann Hula, S.N., Freedman, S.E., Wulf, G., Ballard, K.J., & Schmidt, R.A. (2008). Principles of motor learning in treatment of motor speech disorders. American Journal of Speech-Language Pathology, 17, 277-298.

Freedman, S.E., Maas, E., Caligiuri, M., Wulf, G., & Robin, D.A. (2007). Internal vs. external: oral-motor performance as a function of attentional focus. Journal of Speech, Language, and Hearing Research, 50, 131-136.

Conference Presentations

Freedman, S.E., & Barlow, J.A. (2009). Bilingual production as a function of lexical and sublexical influences. Poster session presented at the American Speech- Language-Hearing Association National Convention, New Orleans, LA, November 2009.

Freedman, S.E., & Barlow, J.A. (2009). Role of neighborhood density and phonotactic probability in bilingual speech production. Poster session presented at the San Diego State University Student Research Symposium, San Diego, CA, February 2009.

Freedman, S.E., & Barlow, J.A. (2008). Influence of lexical and sublexical factors on Spanish word naming. Poster session presented at the American Speech- Language-Hearing Association National Convention, Chicago, IL, November 2008.

Freedman, S.E., & Barlow, J.A. (2008). Lexical and sublexical influences on children’s Spanish production accuracy. Oral presentation at the Conference on Laboratory Approaches to Spanish Phonology, Austin, TX, September 2008.

Freedman, S.E., & Barlow, J.A. (2008). Influence of Spanish proficiency and phonotactic probability on adult Spanish nonword repetition. Oral presentation at the San Diego State University Student Research Symposium, San Diego, CA, March 2008.

xvii

Freedman, S.E., Maas, E., Caligiuri, M., Wulf, G., & Robin, D.A. (2006). Oral-motor learning, retention, and transfer as a function of attentional focus. Poster session presented at the Speech Motor Control Conference, Austin, TX, March 2006.

Freedman, S.E., Maas, E., Caligiuri, M., Wulf, G., & Robin, D.A. (2006). Impact of attentional focus on the oral-facial system. Poster session presented at the UCSD All-Grad Research Symposium, La Jolla, CA, January 2006.

Freedman, S.E., Maas, E., Caligiuri, M., Wulf, G., & Robin, D.A. (2005). The role of attentional focus during oral-motor performance. Poster session presented at the American Speech-Language-Hearing Association National Convention, San Diego, CA, November 2005.

Freedman, S.E., Maas, E., Caligiuri, M., Wulf, G., & Robin, D.A. (2005). Effects of attentional focus on oral-motor control and learning. Poster session presented at the Clinical Aphasiology Conference, Sanibel Island, FL, June 2005.

Teaching Experience

2009 Clinical Supervisor, San Diego State University SLHS 626A Pediatric Speech-Language Pathology Supervised graduate students in speech-language pathology clinical practicum; conducted staffings on various topics of assessment and treatment of child language disorders; facilitated communication between clinicians and caregivers.

2009 Guest Lecturer, San Diego State University SLHS 512 Phonological Acquisition and Disorders Designed and provided a lecture on lexical and sublexical variables of language, presenting issues related to typical and clinical populations.

2008 Guest Lecturer, San Diego State University SLHS 607 Phonology and Phonological Disorders Presented different theories of phonological development, including definitions and examples of various phonological processes that occur in typical and clinical populations.

2008 Guest Lecturer, San Diego State University SLHS 320 Phonetics Designed a lecture and activities covering childhood language acquisition and phonological development for a phonetics class.

2007 Teaching Assistantship, San Diego State University SLHS 608 Motor Speech Disorders xviii

Created and maintained grade database, attended lectures, graded exams, reinforced lecture content individually with students, and determined course grades.

2007 Teaching Assistantship, San Diego State University SLHS 601 Speech Science Instrumentation Designed and presented lab on acoustic analysis, created and maintained electronic grade database, attended lectures, graded exams, reinforced lecture content individually with students, and determined course grades.

2004 Guest Lecturer, San Diego State University SLHS 580 Communication Processes and Aging Designed and provided a lecture on Alzheimer’s disease, including neurological characteristics and associated cognitive deficits.

2004 Teaching Assistantship, San Diego State University SLHS 321 Anatomy and Physiology of the Speech Mechanism (3 lab sections) Created and implemented lab exercises, designed and administered quizzes, maintained electronic grade database, reinforced lecture content, and determined lab grades.

Research Projects and Experience

2008 Whole-word production measures of bilingual children’s phonological development. San Diego State University, Phonological Typologies Laboratory, Dr. Jessica Barlow. 2008 Lexical and sublexical influences on children’s Spanish production accuracy. San Diego State University, Phonological Typologies Laboratory, Dr. Jessica Barlow. 2007 Effects of language proficiency and phonotactic probability on adult nonword repetition. San Diego State University, Phonological Typologies Laboratory, Dr. Jessica Barlow. 2006 Treating specific language impairment in bilingual children with a focus on argument structure and complex vocabulary. San Diego State University, Bilingual Child Language Research Laboratory, Dr. Vera Gutierrez-Clellen. 2005 Code-switching in bilingual children. San Diego State University, Bilingual Child Language Research Laboratory, Dr. Vera Gutierrez-Clellen. 2004 Effects of attentional focus on oral-motor performance. San Diego State University, Motor Speech Laboratory, Dr. Donald Robin. 2004 Treating interarticulator coordination in apraxia of speech with variable practice. San Diego State University, Motor Speech Laboratory, Dr. Donald Robin.

xix

xx Reviewer Experience

American Journal of Speech-Language Pathology

Clinical Experience

2007-2009 Speech-Language Pathologist Laurie Silverman and Associates, San Diego, CA Speech and language services; assessment and treatment of communicative disorders and swallowing impairments in children and adults.

2006-2007 Clinical Fellow Speech-Language Pathologist Balboa Elementary School, San Diego, CA Speech and language services; assessment and treatment of specific language impairment in bilingual preschoolers and Spanish-speaking monolingual children.

2006 Student Speech-Language Pathologist Naval Medical Center, San Diego, CA Speech and language services; assessment and treatment of language, speech, voice, fluency, and swallowing impairments in children and adults.

2004-2005 Student Speech-Language Pathologist San Diego State University Communications Clinic, San Diego, CA Speech and language services; assessment and treatment of language, speech, voice, and fluency disorders in children and adults.

Professional Licenses and Certificates

Certificate of Clinical Competence, American Speech-Language-Hearing Association Speech-Language Pathologist, State of California Speech-Language Pathologist, State of New York

Academic Service

2005-2007 Student Representative, Joint Doctoral Program in Language and Communicative Disorders, San Diego State University and University of California, San Diego

Association Memberships

American Speech-Language-Hearing Association Phi Kappa Phi Honor Society

ABSTRACT OF THE DISSERTATION

A beautiful day in the neighborhood: The influence of neighborhood density on speech production

by

Skott Elliot Freedman

Doctor of Philosophy in Language and Communicative Disorders

University of California, San Diego, 2009 San Diego State University, 2009

Professor Jessica Barlow, Chair

The goal of the current work was to investigate the influence of neighborhood density (ND) on speech production. ND is an index of phonological similarity and refers to the number of meaningful words (neighbors) present in a language that differ xxi

only by adding, deleting, or substituting a phoneme in any word position (Vitevitch & Luce, 1998, 1999). Prior studies of ND have yielded conflicting findings for production, reporting both inhibitory and facilitory effects of ND (Heisler, 2004; Vitevitch, 2002). In order to discern whether words may act more as competitors or facilitators (or potentially neither) during speech production, three experiments were conducted with 39 preschoolers and 46 adults with typical development: Experiment 1 explored influences of ND during children’s picture-naming, Experiment 2 considered effects of ND on adult word repetition, and Experiment 3 discerned the influence of ND during word learning in both age groups. Analyses of production included segmental and whole-word level errors, as well as the lexical nature of production errors. Results revealed varying effects of ND depending upon the task and group. Specifically, children’s naming was facilitated by ND at the semantic level, yet unaffected by ND at the phonological level. Adult word repetition was facilitated by ND in terms of repetition accuracy and the nature of erred repetitions. Finally, an inhibitory effect of ND was found during word learning by children, while adults were seemingly unaffected by the ND manipulation during word learning. Taken together, the results suggest that words do not simply act as competitors or facilitators during speech production; rather, their interactive nature likely depends on the elements of a task and the developing status of the lexicon. Neighbors of a word appeared to generally act as facilitators until a threat was posed, such as when acquiring novel words that were similar in phonological composition to existing words in the lexicon. This research indicates that incorporating ND into experimental or xxii

xxiii treatment paradigms should be used with caution and should be based on the demands of a task as well as the participants involved.

CHAPTER 1 Background and literature review

1

2

INTRODUCTION At first glance, lexical acquisition can seem like an incredibly daunting task. Environmental input presented at a fairly rapid rate must be mapped onto detailed linguistic representations. Specifically, a word’s corresponding semantic properties, phonological segments, and syntactic functions must all be extracted from the incoming speech stream. Surprisingly, this potentially arduous task is typically executed with little effort by children barely a year of age. Moreover, phonological mapping of a novel word can occur with as little as one exposure, even in a naturalistic setting (Carey & Bartlett, 1978). Several theories of lexical acquisition have been proposed to account for this observed ease of learning. One viewpoint attributes facilitated word learning to co- occurrences inherent in the input (Plunkett, 1997; Samuelson & Smith, 1998; Smith, 1995, 1999). For example, children are known to generalize labels of novel objects to other objects similar in shape, regardless of different functions (Jones, Smith, & Landau, 1991). An awareness of such regularities in the environment extends beyond semantics to syntactic, morphological, and phonological cues available in the input. These cues interact during development with other substrates of language, such as the lexicon. Our focus here is on the interaction between phonology and the lexicon. Phonology and the lexicon. The notion that the lexicon significantly affects phonological development was proposed over 30 years ago by Ferguson and Farwell (1975), who argued that “a phonic core of remembered lexical items and the articulations that produced them is the foundation of an individual’s phonology”

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(p. 437). During phonological acquisition, children learn what sounds may occur, in what context, and in what order. Lexical acquisition is thereby facilitated by constraining permissible meaningful forms (Coady & Aslin, 2003). Even with a restricted number of possible phonological structures, though, thousands of potential sound combinations exist. Fortunately, phonological variables embedded in the input appear to assist children in acquiring words at a rapid rate. For instance, consider phonotactic probability, which refers to the probability of sounds occurring and co- occurring in a given language (Vitevitch, Luce, Charles-Luce, & Kemmerer, 1997; Vitevitch & Luce, 1998, 1999). Research findings regarding the effects of phonotactic probability on language use have been fairly consistent for both children and adults, with a high probability advantage found during repetition, naming, and word learning tasks (Munson, 2001; Storkel, 2001; Storkel & Rogers, 2000; Newman & German, 2005). Investigations of related phonological factors, in contrast, have not been nearly as consistent. For example, studies on effects of neighborhood density, relating to the phonological similarity of words, have shown largely conflicting findings with differences occurring between ages, tasks, and domains (perception, production) (Heisler, 2004; Storkel, Armbruster, & Hogan, 2006; Newman & German, 2002, 2005; Vitevitch, 2002; Coady & Aslin, 2003). In this dissertation, we focus on neighborhood density in an attempt to gain a better understanding of its role in speech production by both children and adults and across a variety of tasks.

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Dissertation layout. The organization of this dissertation will be structured as follows. First, the remainder of Chapter 1 will provide a review of the empirical research on neighborhood density on which the subsequent studies are set. Next, the influence of neighborhood density on speech production will be considered across several tasks in Chapters 2 through 4. Chapter 2 explores how neighborhood density may influence children’s accuracy during picture naming, Chapter 3 examines effects of neighborhood density on adult word repetition during noise interference, and Chapter 4 investigates the relationship between neighborhood density and word learning by children and adults on the same task. The final Chapter 5 summarizes the experimental findings, draws appropriate conclusions, considers the theoretical and clinical implications of the findings, and suggests future areas of research that can offer clarification on unresolved issues.

1.0 NEIGHBORHOOD DENSITY 1.0.1 Defining phonological similarity. Neighborhood density (hereafter, ND) refers to the number of meaningful words, or neighbors, present in a given language by adding, substituting, or deleting a phoneme in any word position (Vitevitch & Luce, 1998, 1999). Previous studies have found that using this single- phoneme metric has psychological validity. For example, Luce and Large (2001) reported that when participants were presented with a nonword and asked to produce the closest real word, more than 70% of responses involved a one-phoneme change. Thus, speakers of a language appeared to share similar definitions of phonological

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similarity. Consider the English word “cat” /kæt/. By substituting the first sound, the words “mat” /mæt/, “bat” /bæt/, “sat” /sæt/ (and so on) would be considered neighbors. Similarly, “at” /æt/ is a neighbor of “cat” by deleting the initial segment, as are “can” /kæn/ and “cap” /kæp/, by substituting the final sound. A word with many neighbors, such as the above example of “cat”, is said to reside in a dense neighborhood and have high ND. In contrast, the English word “sniff” /snɪf/, which has few neighbors (e.g., “stiff” /stɪf /, “snuff” /snʌf/), is considered to reside in a sparse neighborhood and have low ND. Research focusing on ND has experienced a surge in the last decade, particularly in areas of phonological acquisition (Gierut, Morrisette, & Champion, 1999; Morrisette & Gierut, 2002), speech perception (Luce & Pisoni, 1998; Vitevitch & Luce, 1998, 1999), word learning (Storkel et al., 2006; Heisler, 2004; Storkel, 2004), and speech production (Newman & German, 2005; Vitevitch, 2002; Gordon & Dell, 2001). Consistent findings have emerged from the speech perception and phonological acquisition literature that words with high ND can inhibit perception in terms of decreased accuracy on perceptual identification tasks (Luce & Pisoni, 1998; Cluff & Luce, 1990; Goldinger, Luce, & Pisoni, 1989), as well as result in the least amount of productive sound change in phonological treatment (Gierut et al., 1999; Morrisette & Gierut, 2002). On the contrary, conflicting and often inconsistent results have been reported for the influence of ND on speech production. Some researchers have reported an advantage for words with low ND (low ND > high ND), and have assumed that words with high ND might inhibit production during naming due to

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lexical competition with similarly-sounding forms (Newman & German, 2002, 2005). Yet, other researchers have described a more facilitative effect of ND (high ND > low ND), which has been argued to be due to increased levels of overall lexical activation (Vitevitch, 2002; Storkel et al., 2006). And finally, null effects of ND (low ND = high ND) have also been reported (Vitevitch, Armbruster, & Chu, 2004). In light of the confusion stemming from prior research, it is presently uncertain whether words may act competitively or facilitatively with one another (or neither) during the speech production process. Alternatively, differences related to stimuli, task, or age may be responsible for the inconsistencies observed across previous findings. The primary goal of the current work therefore was to narrow the existing gap in the literature surrounding how ND may influence speech production in children and adults. 1.0.2 Modeling ND. In addition to investigating effects of ND on production, another goal of the present research program was to better understand how the organization of the lexicon might cause such effects. Previous accounts of the interaction between phonology and the lexicon have typically been represented using connectionist models (Gupta & MacWhinney, 1997; Luce, Goldinger, Auer, & Vitevitch, 2000; see Storkel & Morrisette, 2002, for discussion). Connectionist frameworks presume that words, referred to as nodes, have activation states, and that connection weights exist between these nodes and their neighbors. Activation states and connection weights have often been invoked to explain increased production accuracy for certain types of words, such as those with high frequency. For example, Storkel and Morrisette (2002) presented a two-representational model incorporating

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phonotactic probability (hereafter, PP) and ND, based on existing work (e.g., Gupta & MacWhinney, 1997; Luce et al., 2000). Briefly, a word has two representations in the model. One representation resides at the phonological level and corresponds to a word’s individual sounds and sequences; PP is believed to operate here. The other representation lies at the lexical level and refers to a word as a whole unit; ND is purported to operate here. As a feature of the model, before a word can be produced, its representation must reach a critical level called the activation threshold. This threshold refers to the amount of accumulated activation necessary before a lexical representation enters conscious awareness. A speaker may then select the word to be produced to initiate motor planning stages. Under this model, words with high ND may compete with one another during production if they become activated themselves, thereby delaying the activation threshold for a target item. At the same time, words with high ND might instead facilitate a target word by feeding activation via shared phonological segments. Given that activation has the possibility of being both facilitory and inhibitory in the model, it is difficult to predict under which circumstances (and why) such activation would occur. Additionally, the model does not explain how the organization of the lexicon would lead to such possibilities. For instance, are words with high ND clustered together in a common area of lexical space, or are connection weights sufficiently established regardless of where two words exist in the lexicon? Lastly, although representations must also include information about a word’s meaning and grammatical properties, only a word’s phonological composition is given

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consideration in the two-representational model (Gupta & MacWhinney, 1997; Luce et al., 2000). Consequently, comparisons with other aspects of similarity in the lexicon, such as semantics, are not possible. Such comparisons can shed light on whether aspects of the lexicon (e.g., degree of similarity) are governed by similar underlying principles. By using a model that is capable of defining parameters more generally, we can increase our understanding of the lexicon in a broader context to other real-world cognitive systems. Insight can then be gained into how a network such as the lexicon evolves over time, as well as what factors appear to affect it (e.g., phonological similarity). 1.0.3 Graph theory. In order to examine the possibility that non-connectionist approaches might more generally represent the lexicon in terms of ND, Vitevitch (2008) adopted graph theory. This theory derives from mathematics and has been typically used by computer scientists and physicists to examine the structure of complex systems (for review, see Albert and Barabási, 2002; Barabási, 2002). By definition, complex systems refer to a vast number of individual units interacting in a relatively simple manner (Vitevitch, 2008). One example of such a system is the World Wide Web, where a plethora of individual websites are linked to many others (Pastor-Satorras & Vespignani, 2004). Two key terms necessary for understanding graph theory are nodes and links. Similar to connectionist models, in graph theory, words are represented by nodes, and links are the relationships between two nodes (neighbors). For example, in the World Wide Web, each website is a node, and the

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Abstract: The goal of the current work was to investigate the influence of neighborhood density (ND) on speech production. ND is an index of phonological similarity and refers to the number of meaningful words (neighbors) present in a language that differ only by adding, deleting, or substituting a phoneme in any word position (Vitevitch & Luce, 1998, 1999). Prior studies of ND have yielded conflicting findings for production, reporting both inhibitory and facilitory effects of ND (Heisler, 2004; Vitevitch, 2002). In order to discern whether words may act more as competitors or facilitators (or potentially neither) during speech production, three experiments were conducted with 39 preschoolers and 46 adults with typical development: Experiment 1 explored influences of ND during children's picture-naming, Experiment 2 considered effects of ND on adult word repetition, and Experiment 3 discerned the influence of ND during word learning in both age groups. Analyses of production included segmental and whole-word level errors, as well as the lexical nature of production errors. Results revealed varying effects of ND depending upon the task and group. Specifically, children's naming was facilitated by ND at the semantic level, yet unaffected by ND at the phonological level. Adult word repetition was facilitated by ND in terms of repetition accuracy and the nature of erred repetitions. Finally, an inhibitory effect of ND was found during word learning by children, while adults were seemingly unaffected by the ND manipulation during word learning. Taken together, the results suggest that words do not simply act as competitors or facilitators during speech production; rather, their interactive nature likely depends on the elements of a task and the developing status of the lexicon. Neighbors of a word appeared to generally act as facilitators until a threat was posed, such as when acquiring novel words that were similar in phonological composition to existing words in the lexicon. This research indicates that incorporating ND into experimental or treatment paradigms should be used with caution and should be based on the demands of a task as well as the participants involved.