Disentangling Dyslexia

Name: Disentangling Dyslexia
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Author: Maria Vender
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Vender, Maria

Disentangling Dyslexia

Phonological and Processing Deficit in Developmental Dyslexia

by Maria Vender (Author)

Linguistics

Series: Linguistic Insights, Volume 212

Summary

Beyond the well-known reading and spelling difficulties, dyslexic individuals exhibit marked phonological disorders, poor lexical retrieval and problems in the comprehension and production of grammatical structures that are particularly expensive in terms of processing costs. To account for these difficulties, the author presents an original hypothesis, proposing that dyslexia is related to a working memory inefficiency, affecting in particular the subject’s phonological skills and executive functions. The results of four experimental protocols, assessing dyslexic children’s working memory and their ability to interpret scalar implicatures, negative sentences and pronominal expressions, are presented and discussed in this volume. Consistent with the hypothesis outlined in this book, the results of the four studies show that dyslexics underperformed in comparison to age-matched controls and even to younger children in tasks requiring good phonological and processing abilities.

Excerpt

Cover
Title
Copyright
About the author
About the book
This eBook can be cited
Contents
Acknowledgments
Preface
Chapter 1. An Introduction To Developmental Dyslexia
1. Introduction
2. On the difficulty to find a comprehensive definition of Developmental Dyslexia
3. Manifestations of Developmental Dyslexia
3.1. Reading difficulties
3.1.1. A theoretical approach to reading: the Dual-Route Model
3.1.2. The development of reading: Frith’s model of learning to read
3.2. Spelling difficulties
3.3. Phonological deficits
3.4. Vocabulary development and lexical retrieval
3.5. Grammatical deficits
3.5.1. The Interpretation of Tough Sentences
3.5.2. The Interpretation of Pronouns
3.5.3. Comprehension and Production of Relative Clauses
3.5.4. The Interpretation of Passive Sentences
3.5.5. The Interpretation of Grammatical Aspect
3.5.6. Morphosyntactic Agreement
3.6. Attention deficits
3.7. Motor deficits
4. Precursors of Dyslexia
5. Summary and Conclusions
Chapter 2. Developmental Dyslexia: Theoretical Perspectives
1. Introduction
2. The Visual Deficit Hypothesis
3. The Auditory Deficit Hypothesis
4. The Magnocellular Deficit Hypothesis
4.1. The Magnocellular Systems and its disruption in Dyslexia
4.2. Reading deficits as a consequence of magnocellular disorders
5. The Phonological Deficit Hypothesis
5.1. Deficit or delay? The Developmental Lag Hypothesis
5.2. Phonological deficits causing or caused by poor reading?
5.3. Underspecified phonological representations or difficulties in accessing them?
5.4. Strengths and weaknesses of the Phonological Deficit Hypothesis
6. The Double Deficit Hypothesis
7. The Working Memory Deficit Hypothesis
7.1. What is Working Memory?
7.2. Baddeley and Hitch’s Original Model of Working Memory
7.2.1. The Phonological Loop
7.2.1.1. The Phonological Loop and Language Competence: evidence from language disordered and language gifted people
7.2.2. The Visuo-Spatial Sketchpad
7.2.3. The Central Executive
7.2.4. The Episodic Buffer
7.3. Baddeley’s revised Model of Working Memory
7.4. Working Memory and Development
7.5. Working Memory, Cognitive Skills and Neuro-developmental Disorders
7.6. Working Memory and Dyslexia
8. Summary and Conclusions
Chapter 3. Working Memory Skills In Developmental Dyslexia
1. Introduction
2. Participants
3. General Design and Procedure
3.1. Tasks assessing the functioning of the Phonological Loop
3.1.1. Digit Recall
3.1.2. Word List Matching
3.1.3. Word List Recall
3.1.4. Nonword List Recall
3.2. Tasks assessing the functioning of the Visuo-Spatial Sketchpad
3.2.1. Block Recall
3.2.2. Mazes Memory
3.3. Tasks assessing the functioning of the Central Executive
3.3.1. Listening Recall
3.3.2. Counting Recall
3.3.3. Backward Digit Recall
4. Results
4.1. The Phonological Loop
4.2. The Visuo-Spatial Sketchpad
4.3. The Central Executive
5. General Discussion
6. Summary and Conclusions
Chapter 4. The Phonological and Executive Working Memory Deficit Hypothesis
1. Introduction
2. Working Memory and Human Cognition
3. Working Memory and Language Comprehension
3.1. The comprehension of garden path and ambiguous sentences
3.2. The comprehension of object relative clauses
3.3. Further evidence in favor of the Capacity Constrained Comprehension Theory: extrinsic memory load and distance effects
3.4. Is there a general verbal Working Memory or a specific and independent WM for language comprehension?
4. The Phonological and Executive Working Memory Deficit Hypothesis
4.1. How the hypothesis explains reading and spelling deficits
4.2. How the hypothesis explains phonological deficits
4.3. How the hypothesis explains vocabulary and naming deficits
4.4. How the Phonological and Executive Working Memory Deficit Hypothesis explains grammatical deficits
4.4.1. The Interpretation of Tough Sentences
4.4.2. The interpretation of pronouns
4.4.3. The Interpretation of Relative Clauses
4.4.4. The Interpretation of Passive Sentences
4.4.5. The Interpretation of Grammatical Aspect
4.5. How the hypothesis accounts for morphosyntactic deficits
4.6. How the hypothesis accounts for attention deficits
5. Summary and Conclusions
Chapter 5. The Computation of Scalar Implicatures in Developmental Dyslexia
1. Introduction
2. What are Scalar Implicatures?
2.1. The interpretation of scalar expressions in downward entailing contexts
3. The computation of scalar implicatures: the Structural and the Pragmatic Approach
3.1. Experimental studies assessing Scalar Implicatures’ computation
3.1.1. The computation of Scalar Implicatures in children: acquisitional data
3.1.2. The computation of Scalar Implicatures in adults: experimental data
3.2. The Reference-Set Computation
4. Experimental Protocol
4.1. Experiment 1: a statement evaluation task
4.1.1. Participants
4.1.2. Design and Procedure
4.1.3. Results
4.1.4. Discussion
4.2. Experiment 2: the interpretation of quantifiers
4.2.1. Participants
4.2.2. Design and Procedure
4.2.3. Results
4.2.4. Discussion
4.3. Experiment 3: the interpretation of frequency adverbs
4.3.1. Participants
4.3.2. Design and Procedure
4.3.3. Results
4.3.4. Discussion
4.4. Experiment 4: The interpretation of disjunction
4.4.1. Participants
4.4.2. Design and Procedure
4.4.3. Results
4.4.4. Discussion
4.5. Experiment 5: A Felicity Judgment Task
4.5.1. Participants
4.5.2. Design and Procedure
4.5.3. Results
4.5.4. Discussion
5. General discussion
6. Summary and Conclusions
Chapter 6. The Interpretation of Negation in Developmental Dyslexia
1. Introduction
2. The semantics of negation
2.1. Negation in classical logic
2.2. Negation and presuppositions
2.3. Markedness of negation
3. Processing of negation
3.1. The earlier experimental studies on negation: Wason (1961) and Carpenter and Just (1975)
3.2. First solutions: Wason’s “context of plausible denial” and the pragmatic theory of negation
3.3. Carpenter and Just’s Psycholinguistic Model of Sentence Verification
3.4. Negation and Accessibility
3.5. Kaup, Lüdtke and Zwaan (2007): The Two-Step Simulation Hypothesis
3.6. An original proposal to account for the processing of negation in sentence-picture verification tasks: The Model of Sentence-Picture Match Processing for Negative Sentences
4. Experimental Protocol
4.1. Participants
4.2. Design and Procedure
4.2.1. Experiment 1: The interpretation of negative sentences
4.2.2. Experiment 2 – The interpretation of passive negative sentences
4.3. Results
4.3.1. Results of Experiment 1
4.3.2. Results of Experiment 2
4.4. General Discussion
5. Summary and Conclusions
Chapter 7. The Interpretation of Pronominal Expressions in Developmental Dyslexia
1. Introduction
2. The interpretation of referential expressions in the Accessibility Theory
2.1. How the Accessibility Theory works
2.2. Processing costs of Accessibility Theory
2.3. The interpretation of zero pronouns and phonetically realized pronouns
3. Processing costs of zero pronouns’ and phonetically realized pronouns’ resolution: A proposal
4. Experimental Protocol
4.1. Participants
4.2. Design and Procedure
4.3. Results
4.4. Discussion
5. Summary and Conclusions
Chapter 8. Concluding Remarks
1. Introduction
2. The Cerebellar Deficit Hypothesis
2.1. Ullman’s Declarative/Procedural Model
3. The Phonological and Executive Working Memory Deficit Hypothesis and the Cerebellar Deficit Hypothesis: a comparison between the two hypotheses
4. Summary and Conclusions
References
Series Index

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Acknowledgments

This book is an extended version of my PhD Dissertation at the University of Verona, which was submitted and defended in the spring of 2011. Although the general structure of the dissertation is preserved, several modifications have been added, thanks to the many constructive comments and suggestions that I have received in these years.

I am very grateful to Denis Delfitto, my thesis advisor, who always supported my work, encouraging me to follow my intuitions, and who suggested me to transform my dissertation in this book: significant parts of it are based on joint work with him.

Writing this book has proven to be a big challenge and a valuable experience, to which I devoted most of my time, energies and passion. As every small and great challenge, this work would not have been possible without the precious help of many people. I am very obliged to Chiara Melloni, who supported me in the idea to publish this book, offering constant help and mindful suggestions. A special thank you also to my colleagues, Federica Mantione and Maria Scappini, and to all the people who have assisted me in this adventure and during the PhD, discussing and supporting my projects and ideas with interesting comments and suggestions: Birgit Alber, Adriana Belletti, Pier Marco Bertinetto, Camilla Bettoni, Sibilla Cantarini, Roberto Cubelli, Elise de Bree, Maria Teresa Guasti, Gaetano Fiorin, Francesca Forza, Giorgio Graffi, Shenai Hu, Karin Martin, Elena Menegazzo, Jacques Moeschler, Paola Paradisi, Stefan Rabanus Anne Reboul, Danilo Reggiani, Christian Retoré, Silvia Savazzi, Alessandra Tomaselli, Jacopo Torregrossa, Francesco Vespignani, Mirta Vernice, Frank Wijnen.

I am very indebted to all the people and institutions that helped in the organization of the experiments presented in this work: first of all, I wish to thank all the children who participated in the experimental sessions with great enthusiasm and all their families. I am also grateful to the directors and the speech-therapists of the “Centro Audiofonetico” in Trento, of the “Dipartimento di Neuropsichiatria Infantile” ULLS 20 ← 13 | 14 → in Verona, and of the “U.O. di Neuropsichiatria Infantile” in Rovereto (Trento), who helped in the recruitment of the dyslexic children. Thanks to all the directors and the teachers of the schools who collaborated with us and helped in the recruitment of the children: “Istituto Comprensivo di Fondo” in Romeno (Trento), “Istituto Comprensivo di Revò” in Revò and Banco (Trento), “Istituto Comprensivo di Cles” in Livo (Trento), “Scuola Elementare Aleardi” in Quinto di Valpantena (Verona), “Scuola Materna Paolo Crosara” in S. Bonifacio (Verona) and “Scuola Equiparata dell’Infanzia” in Cles (Trento).

Thanks to Gaetano Fiorin, Karin Martin, Luisa Piccoli and Danilo Reggiani, who helped administering the experiments.

A final and special thanks goes to my whole family and to my friends, to my husband Nicola, who has always supported me, and to my children, Gabriele, Angelica and Aurora, my real source of inspiration.

← 14 | 15 →

Preface

In this book, I will review some of the most peculiar aspects concerning developmental dyslexia, focusing on its distribution and, especially, on its manifestations and possible causes.

Observing that dyslexic individuals appear to manifest severe deficits in those cognitive tasks which require a fine phonological analysis and which are particularly demanding in terms of processing resources, I will propose an original hypothesis to account for the cognitive impairment underlying this disorder, the Phonological and Executive Working Memory Deficit Hypothesis, reported below.

The Phonological and Executive Working Memory Deficit Hypothesis

Dyslexic individuals suffer from a limitation affecting their Working Memory and hampering in particular their phonological memory and their executive functions. As a consequence, this impairment disrupts their phonological competence, as well as their performance in complex tasks that are particularly demanding in terms of Working Memory resources. On the contrary, dyslexics can rely on a spared visuo-spatial memory, to which they can resort for the accomplishment of compensatory strategies.

As I will discuss in this book, Working Memory is the brain system engaged in the temporary storage and manipulation of the information that is necessary for cognitive tasks such as reasoning, learning, problem solving, language comprehension. Specifically, I will adopt as a starting point for my analysis Baddeley and Hitch’s (1974) influential Working Memory Model, according to which Working Memory is constituted by two short-term stores, the Phonological Loop and the Visuo-Spatial Sketchpad, and a limited capacity attentional controller supervising all the activities, the Central Executive. The two short-term stores, which are independent from each other, are concerned respectively with the temporary storage of phonological information and of visuo-spatial information. The Central Executive, instead, is involved in executive functions, that is in the control of attention, detecting the ← 15 | 16 → relevant stimuli and filtering out those that are irrelevant, in the supervision of the activities carried out by the two slave-subsystems and in the manipulation and execution of the operations. In a subsequent version of the model, these functions are partially accomplished by a fourth component, the Episodic Buffer, which is a subsystem supporting a multimodal code and concerned with the manipulation and integration of the information provided by the two short-term stores.

Adopting this framework, I will review recent experimental results demonstrating that Working Memory, and in particular the Central Executive, plays a fundamental role in human cognition. Individual differences in cognitive tasks are determined by the general capacity of the individual’s Working Memory: people whose Working Memory is limited or less efficient are more likely to show lower speed and accuracy in the execution of complex tasks that are demanding in terms of processing resources.

In the Phonological and Executive Working Memory Deficit Hypothesis, I propose that developmental dyslexia is characterized by the presence of two main impairments affecting dyslexics’ Working Memory. On the one side, in fact, dyslexic individuals suffer from a phonological memory deficit, preventing them from correctly analyzing the internal structure of words and nonwords. On the other side, instead, they show an impairment affecting their executive functions and hampering their performance in complex and demanding tasks. The severity of these impairments determines the severity of the disorder itself.

A clear consequence of this hypothesis is that dyslexic individuals are expected to exhibit difficulties whenever they are asked to perform complex operations or to execute more than one task simultaneously. Nevertheless, some compensation is allowed by the general plasticity of the system: an individual with a high IQ score, for instance, can learn to use alternative strategies to perform a task in order to circumvent her difficulties.

Throughout this discussion, I will show that the Phonological and Executive Working Memory Deficit Hypothesis is able to account for all the core manifestations of developmental dyslexia, explaining not only the well-known reading and spelling difficulties that characterize the disorder, but also the frequently reported phonological deficits, vocabulary and naming disorders, grammatical impairments and attention problems. ← 16 | 17 →

The book is organized as follows. In Chapter 1, I will present a detailed introduction to developmental dyslexia, discussing the manifestations of the disorder, and focusing on recent studies developed to identify the precursors of dyslexia.

Chapter 2, instead, will be dedicated to the illustration of the main theories proposed to explain the causes of dyslexia, ranging from the Visual and Auditory Deficit Hypotheses and moving to the more recent approaches, such as the Magnocellular Deficit Hypothesis, the Phonological Deficit Hypothesis, the Double Deficit Hypothesis and the Working Memory Deficit Hypothesis. Discussing both strengths and weaknesses of each proposal, I will argue that none of them is able to capture all the difficulties associated with dyslexia, except for the Working Memory Deficit Hypothesis. However, I will suggest that this proposal should be reformulated more precisely and that it is actually in need of some further experimental corroboration, by means of experimental protocols designed to accurately test dyslexic children’s and age-matched typically developing children’s Working Memory.

The results of this experimental protocol will be presented in Chapter 3. As I will observe, findings provide uncontroversial evidence in favor of an impairment affecting dyslexics’ Phonological Loop and Central Executive, but leaving their Visuo-Spatial Sketchpad spared and normally functioning.

Considering these results as a starting point, I will propose my hypothesis, the Phonological and Executive Working Memory Deficit Hypothesis outlined above, in Chapter 4. Specifically, I will argue that dyslexics’ poorly functioning phonological memory and executive functions hamper their performance in tasks requiring a good phonological competence and demanding a high amount of cognitive resources. I will note, therefore, that dyslexics’ deficits are more likely to arise in complex tasks.

In order to further test the Phonological and Executive Working Memory Deficit Hypothesis I decided to assess dyslexic children’s performance in linguistically complex tasks, developing three experimental protocols whose results will be presented in the subsequent chapters. ← 17 | 18 →

In Chapter 5, I will discuss the result of a first protocol testing dyslexic children’s ability to compute scalar implicatures, an operation remarkably expensive in terms of processing resources, comparing their performance to that shown by age-matched typically developing children, a group of younger children and a group composed by adults.

In Chapter 6, I will present a second experiment testing the interpretation of negation in dyslexic children and age-matched typically developing children, considering their ability to comprehend negative active and passive sentences.

Finally, in Chapter 7, I will expose the results of a last protocol assessing dyslexic children’s competence in the interpretation of pronouns, comparing their performance to that shown by age-matched control children, control adults and two groups of younger children.

As I will argue throughout the discussion, all three experiments provided results that are consistent with the Phonological and Executive Working Memory Deficit Hypothesis, demonstrating that dyslexics are indeed remarkably more impaired than their peers in the comprehension of complex sentences. Moreover, their performance is strikingly similar to that shown by children who are 2 or 4 years younger.

Finally, Chapter 8 will be dedicated to the concluding remarks: I will summarize the considerations put forward throughout the book and I will propose a new definition of developmental dyslexia, which focuses on the phonological and executive Working Memory impairment exhibited by dyslexic individuals. I will also briefly introduce and discuss the Cerebellar Deficit Hypothesis developed by Nicolson and colleagues (1995, 2001, 2008) to explain dyslexia.

I will argue that the Cerebellar Deficit Hypothesis and the Phonological and Executive Working Memory Deficit Hypothesis present both commonalities and differences and that further research is needed to analyze more thoroughly the distinct predictions made by the two proposals.

← 18 | 19 →

Chapter 1

An Introduction To Developmental Dyslexia

1. Introduction

Developmental Dyslexia is a learning based disability that interferes in particular with the acquisition of language. This disorder, which has a clear neurologic and genetic origin, affects around 5–15% of the population and it is highly inheritable. It is namely widely acknowledged that dyslexia runs in families: it is estimated that a child with a dyslexic parent or sibling has 50% probability of being dyslexic (Gayan and Olson 1999).

A difference between the sexes has also been found, with a sex ratio of approximately three or four males to one female (Wolff and Melngailis 1994). This discrepancy appears to increase in parallel to the severity of the disorder and to the IQ of the subject: as the reading deficit becomes more severe, the IQ tends to be lower and the male ratio tends to be higher (Olson 2002). However, the imbalance between the sexes may sometimes be overestimated, due to the tendency reported by teachers to identify boys as being more problematic than girls in class.

One of the most easily detectable symptoms of dyslexia, to which this disorder actually owes its name, is the failure to acquire properly reading and spelling skills. This impairment appears to be particularly surprising in those children, as dyslexics, who are otherwise intelligent and adequately exposed to literacy. Specifically, as we will observe throughout this book, dyslexics perform very poorly when asked to read irregular words or non-words. Obviously, these difficulties are even more evident in languages with an ‘opaque’ orthography, as English, where there is more than one possible mapping between a letter and its sound (consider the pronunciation of the phoneme /əʋ/ in the words “so”, “road”, “bowl”, “though”). In these languages phoneme-grapheme correspondence rules are less reliable than in transparent languages, such as Italian, where ← 19 | 20 → mappings between phonemes and graphemes are more regular and children have more chances to read properly both regular and irregular words.

This cross-linguistic discrepancy can be held responsible for the different percentages concerning the distribution of dyslexia that can be found across countries: in Italy, in fact, it is argued that dyslexia affects 3–4% of the population ¹, whereas the percentage raises to reach 15–20% in the USA². Of course, this discrepancy does not imply that dyslexia is more widespread in one country than in another one; it simply reflects the fact that it is easier to detect reading difficulties in children whose mother-tongue has an opaque orthography. On the contrary, the difficulties experienced by those children whose mother-tongue has a transparent orthography may go unnoticed.

However, although it appears that reading difficulties are the most significant and important problem exhibited by dyslexics, we will observe throughout the discussion that reading failure is just one of the symptoms of dyslexia, which is definitely a more complex and multifaceted disorder. Other frequently reported manifestations of dyslexia are impairments in those speech processes which require both accuracy of phonological processing and speed, such as picture naming tasks (Swan and Goswami 1997a), tasks tapping phonological awareness (Swan and Goswami 1997b), testing the repetition of words and nonwords (Miles, 1993) and verbal working memory performance (Nelson and Warrington 1980, Gathercole et al. 2006).

Details

Pages: 356
Year: 2017
ISBN (PDF): 9783034329637
ISBN (ePUB): 9783034329644
ISBN (MOBI): 9783034329651
ISBN (Softcover): 9783034320641
DOI: 10.3726/b11503
Language: English
Publication date: 2017 (August)
Keywords: Developmental Dyslexia Working Memory Phonological Deficit Processing Deficit Pronouns Negation Scalar Implicatures
Published: Bern, Berlin, Bruxelles, Frankfurt am Main, New York, Oxford, Wien, 2017. 338 pp., 28 b/w ill., 1 coloured ill., 25 b/w tables, 11 graphs

Biographical notes

Maria Vender (Author)

Maria Vender is a Postdoc Researcher and Adjunct Professor at the University of Verona. Her research interests concern the investigation of the linguistic and cognitive deficits in learning and language disabilities, focusing on the relationship between dyslexia, bilingualism and foreign language learning.

Disentangling Dyslexia

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