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Disentangling Dyslexia: Phonological and Processing Impairment in Developmental Dyslexia
No full textAim of this work is to analyze thoroughly the most peculiar aspects of Developmental Dyslexia, focusing on its distribution and, especially, on its manifestations and possible causes, and to propose an original hypothesis able to account for the cognitive impairment underlying this disorder. It has been demonstrated in fact that dyslexia is not just an impairment preventing children from learning to read and spell properly, but that it is a more complex and articulated syndrome. Beyond the well-known reading and spelling difficulties, dyslexic individuals exhibit marked phonological disorders, vocabulary deficits and poor lexical retrieval, and problems in the comprehension of complex grammatical structures which involve high processing costs to be interpreted. Moreover, dyslexia is often associated to attention deficits arising in particular when the subject is required to focus on relevant stimuli filtering out those that are irrelevant and distracting. After a deep discussion of these aspects, the author analyzes the main theories developed through the decades to account for dyslexia, proposing then an original hypothesis able to account for all the manifestations associated to the disorder, the Phonological and Executive Working Memory Deficit Hypothesis. The results of an original experimental protocol reported in the book demonstrate that dyslexics 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, resulting in poor reading and spelling skills, slows down their vocabulary development, and hampers their performance in complex tasks which are particularly demanding in terms of Working Memory resources. Three experimental protocols reviewed in the book have been developed to test this hypothesis, analyzing the comprehension of complex structures such as the interpretation of scalar implicatures, negative sentence and pronominal expressions. Consistently with the hypothesis presented in this work, results confirm that dyslexic children have significant difficulties in comparison to age-matched and even younger controls, suggesting that their 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
Disentangling Dyslexia - Phonological and Processing Impairment in Developmental Dyslexia
Full text linkIl presente lavoro di tesi nasce con il duplice obiettivo di sviluppare un’analisi approfondita degli aspetti più peculiari della dislessia evolutiva, quali la distribuzione del disturbo e le sue principali manifestazioni, e di avanzare un’ipotesi originale in merito alle sue possibili cause.
Decenni di ricerche condotte in campo internazionale hanno infatti dimostrato come la dislessia evolutiva non sia un semplice disturbo che ostacola unicamente l’apprendimento della lettura e della scrittura, ma costituisca piuttosto una sindrome complessa ed articolata.
A fianco delle più note difficoltà nel campo dell’alfabetizzazione, infatti, i soggetti dislessici presentano deficit marcati nell’ambito fonologico, che rendono particolarmente gravoso il compito di analizzare la struttura interna delle parole. Tale scarsa consapevolezza meta-fonologica può essere considerata alla base delle difficoltà nell’acquisizione delle regole di conversione grafema-fonema che sottendono l’apprendimento della letto-scrittura. Ad essa si aggiungono disturbi specifici del lessico, che appare essere meno sviluppato nei dislessici, e difficoltà nei cosiddetti rapid-naming tasks, nei quali viene richiesto ai partecipanti di nominare il più rapidamente possibile immagini di semplici oggetti, colori e simboli alfanumerici.
Interessanti studi condotti più recentemente in campo linguistico, inoltre, hanno messo in luce come i dislessici presentino notevoli difficoltà nella comprensione di strutture grammaticali complesse che richiedono elevati costi di processing per essere correttamente interpretate.
A questi disturbi di tipo linguistico, infine, si associano anche estese difficoltà di attenzione e, in particolare, una significativa incapacità di concentrarsi sugli stimoli rilevanti al perseguimento del proprio obiettivo, filtrando quelli irrilevanti.
Partendo dall’analisi di tali manifestazioni della dislessia, obiettivo primario di questa tesi è stato quello di valutare le ipotesi elaborate nel corso dei decenni per spiegare l’eziologia del disturbo, a partire dalle più tradizionaliste ipotesi sensoriali, che considerano la dislessia un problema di tipo visivo o uditivo, per arrivare a teorie più recenti, come quella del deficit magnocellulare, del deficit fonologico e del doppio-deficit. Dal momento che tali ipotesi, pur presentando spunti interessanti, si sono rivelate incapaci di spiegare la totalità delle manifestazioni associate alla dislessia, la ricerca oggetto della presente dissertazione si è prefissa l’obiettivo di sviluppare una nuova proposta che potesse fornire una spiegazione più completa del disturbo.
Tale ipotesi, che chiameremo “Ipotesi del deficit di Memoria di Lavoro Fonologica ed Esecutiva”, prende spunto dai numerosi studi condotti in campo internazionale che hanno messo in luce come i dislessici presentino deficit molto marcati nei test che analizzano la loro memoria di lavoro.
Per quando riguarda l’architettura della memoria di lavoro umana, si è adottato il modello sviluppato da Baddeley ed Hitch (1974) e successivamente affinato da Baddeley (2000), secondo il quale la memoria di lavoro è costituita dall’Esecutivo Centrale, un sistema dotato di compiti di controllo, supervisione e gestione dell’attenzione, e deputato a dirigere le attività di due magazzini a breve termine, il Loop Fonologico e il Taccuino Visuo-Spaziale, che si occupano rispettivamente del mantenimento temporaneo di informazioni di tipo fonologico e visuo-spaziale. A questi due sotto-sistemi ne è stato recentemente aggiunto un terzo, il Buffer Episodico, il quale, essendo in grado di supportare un codice multimodale, ha il compito di integrare le informazioni provenienti dal Loop Fonologico e dal Taccuino Visuo-Spaziale.
In modo da testare in maniera specifica la memoria di lavoro nei bambini dislessici, confrontando la loro performance con quella dei coetanei normodotati, è stato sviluppato e applicato un primo protocollo sperimentale che ha dimostrato, in linea con i risultati ottenuti in altri studi condotti in campo internazionale, come i dislessici presentino marcati deficit a livello di Loop Fonologico e di Esecutivo Centrale, mentre la loro performance nei compiti di memoria a breve termine visuo-spaziale rientra nella norma.
Sulla base di questi risultati, l’Ipotesi del Deficit di Memoria di Lavoro Fonologica ed Esecutiva propone che la dislessia sia un disturbo strettamente connesso ad una limitazione della memoria di lavoro e in particolare della memoria fonologica a breve termine e delle funzioni esecutive.
La conseguenza più evidente del malfunzionamento del Loop Fonologico è rappresentata dall’incapacità di analizzare correttamente la struttura interna delle parole, che si manifesta da un lato nella scarsa consapevolezza meta-fonologica frequentemente diagnosticata nei dislessici, e dall’altro nella loro difficoltà di acquisizione delle corrette regole di conversione grafema-fonema. Dal momento che una delle funzioni attribuite al Loop Fonologico è quella di avere un ruolo determinante nella costruzione del vocabolario dell’individuo e nell’accesso lessicale, ipotizzarne un malfunzionamento permette di spiegare anche le limitazioni del lessico e le difficoltà nei rapid-naming task riportate nei dislessici.
Un disturbo all’Esecutivo Centrale, invece, comporta notevoli problemi nello svolgimento di compiti che richiedono risorse elevate in termini di processing, ovvero che necessitano l’immagazzinamento temporaneo e la manipolazione di più fonti di informazione, nonché l’elaborazione simultanea di più procedure. Ne sono un esempio concreto le difficoltà di comprensione di strutture linguistiche complesse, tipicamente riscontrate nella dislessia. Inoltre, essendo l’Esecutivo Centrale direttamente coinvolto nella gestione e nel controllo dell’attenzione, la sua compromissione può essere ritenuta responsabile dei deficit di attenzione spesso riportati nei dislessici.
Per testare ulteriormente questa ipotesi sono stati sviluppati tre protocolli sperimentali volti ad analizzare la performance dei dislessici nella comprensione di strutture complesse, quali le implicature scalari, la negazione e i pronomi. Compatibilmente con quanto predetto dall’ipotesi di riferimento, i bambini dislessici hanno manifestato significative difficoltà in tutti e tre i protocolli, dimostrando ancora una volta come i problemi emergano chiaramente nei compiti che richiedono costi cognitivi elevati. Nello specifico, i risultati hanno evidenziato che i dislessici non solo commettono più errori dei coetanei normodotati, ma presentano una performance simile a quella di bambini di due e quattro anni più giovani di loro, addirittura di età prescolare.
In conclusione, l’Ipotesi del Deficit di Memoria di Lavoro Esecutiva e Fonologica è potenzialmente in grado di spiegare tutte le manifestazioni connesse alla dislessia e discusse in questa tesi. Tale ipotesi si pone pertanto come un punto di partenza per lo sviluppo di future analisi e prospettive sulla dislessia evolutiva, nonché per l’elaborazione di strumenti diagnostici e di riabilitazione sempre più precisi ed adeguati.In the present dissertation 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.
Working Memory is the brain system engaged in the temporary storage and manipulation of those information that are necessary for those cognitive tasks such as reasoning, learning, problem solving, language comprehension and comprehension and it plays a fundamental role in human cognition. Individual differences in cognitive tasks are determined by the general capacity of their Working Memory: people whose Working Memory is limited or less efficient are more likely to show lower speed and accuracy in the execution of those complex tasks which 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 their 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, a compensation is allowed by the general plasticity of the system: an individual with an 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 principal 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.
The dissertation 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. Moreover, I will briefly introduce the neurobiological aspects of the disorder.
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 Phonological and Executive 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 Phonological and Executive Working Memory Deficit Hypothesis. However, I will suggest that this proposal should be reformulated more precisely and, first of all, strengthened by a further experimental protocol developed to test precisely 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, 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.
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 sentences, negative quantifiers and negative concord.
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 which 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, and that their performance is similar to that shown by children who are 2 or 4 years younger than them.
Finally, Chapter 8 will be dedicated to the concluding remarks: I will summarize the considerations put forward throughout the dissertation 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
POTENZIARE LA CONSAPEVOLEZZA MORFOLOGICA NELLA LETTURA E NELLA COMPRENSIONE DEL TESTO IN ITALIANO IN CONTESTI DI FRAGILITÀ LINGUISTICA
Full text linkIn questo contributo si approfondisce il ruolo della consapevolezza morfologica nella letto-scrittura, evidenziandone l’importanza sia per la decodifica, che per l’arricchimento del vocabolario e la comprensione del testo. Si osserva in particolare come le abilità morfologiche possano costituire una via di compensazione per le difficoltà di lettura in popolazioni con fragilità linguistiche, quali studenti con diagnosi di dislessia evolutiva o con italiano L2. In questa prospettiva, si mette in luce l'importanza di proporre attività volte a potenziare le abilità morfologiche nel contesto scolastico, riportando alcune indicazioni pedagogiche mirate per l’implementazione di un intervento da proporre in chiave inclusiva.
Enhancing morphological awareness in reading and text comprehension in Italian in contexts of linguistic fragility
This paper delves into the role of morphological awareness in reading and writing, highlighting its importance for decoding, text comprehension and lexical development. It is observed, in particular, how morphological skills can serve as a compensatory strategy for reading difficulties in populations with linguistic fragility, such as students diagnosed with developmental dyslexia or those learning Italian as a second language (L2). In this perspective, the importance of proposing activities aimed at enhancing morphological skills in the school context is emphasized, providing some targeted pedagogical indications for the implementation of an inclusive pedagogical intervention
Morphological awareness in developmental dyslexia: Playing with nonwords in a morphologically rich language
Full text linkAlthough phonological deficits are unanimously recognized as one of the key manifestations of developmental dyslexia, a growing body of research has reported impairments in morphological abilities. Our study aimed at casting further light on this domain by investigating the morphological awareness skills of 21 children with dyslexia (mean age 9.10 years old) and 24 children with typical development (mean age 10.3 years old). All children were monolingual speakers of Italian, which is a morphologically rich language characterized by complex inflectional and derivational paradigms. We developed an experimental protocol inspired by Berko’s Wug test and composed of 11 tasks addressing inflectional and derivational processes. Participants were asked to manipulate nonwords of various lexical categories, modeled after the phonotactic structure of Italian, and manipulation involved both word formation and base retrieval. Conditions of the experiments were based on verb conjugation classes differing in frequency, productivity, regularity, and formal transparency. Results confirmed that morphological skills are impaired in dyslexic children, who performed significantly more poorly than their age-matched peers in all tasks. Children with dyslexia were especially challenged by tasks and conditions requiring advanced morphological awareness skills, such as the retrieval of infinitives of infrequent and irregular conjugation classes. The educational and clinical implications of these findings are discussed
Bridging the Gap in Adult Dyslexia Research: Assessing the Efficacy of a Linguistic Intervention on Literacy Skills
Full text linkWhile developmental dyslexia has been extensively studied in children, research on adults is still rather limited. This paper aims to bridge the gap in existing research by presenting the findings of a study that examined the reading and spelling skills of adults with dyslexia and assessed the effectiveness of a linguistic intervention designed to improve their literacy abilities. To address this issue, we first compared the profiles of 44 adults with dyslexia (age range: 16-30 y.o.) and 44 age-matched typical readers across tasks assessing reading, spelling, phonological awareness, morphological awareness and lexical access in Italian. The findings underscored pervasive impairments in dyslexia across all measured dimensions, reaffirming the persistent nature of language and literacy challenges into adulthood. In pursuit of the second objective, the study explored the potential for literacy skill improvement in adults with dyslexia through the implementation of a specialized intervention proposed to 24 dyslexic adults and delivered via a web application. The intervention program yielded positive outcomes in the experimental group, demonstrating significant improvements in word and text reading, spelling, and speed of phonological elaboration. This study, hence, contributes not only to our understanding of developmental dyslexia in adulthood but also emphasizes the tangible benefits of targeted linguistic interventions, thereby offering practical implications for the amelioration of literacy skills in this population
Towards a pragmatics of negation: the interpretation of negative sentences in developmental dyslexia
No full textIn this paper, we present the results of an experimental protocol suggesting the existence of a close relationship between developmental dyslexia, the interpretation of negative sentences and Verbal Working Memory. Recent studies conducted on developmental dyslexia have demonstrated that it is strictly related to a deficit affecting the verbal component of Working Memory. Moreover, research on negation has revealed that negative sentences are more difficult to interpret than their affirmative counterparts. According to the Two-Step Simulation Hypothesis (Kaup et al. 2007), negative sentences require the construction and comparison of two representations, concerning respectively the expected and the asserted state of affairs: an operation remarkably demanding in terms of working memory resources. Significantly, the results of our experimental protocol, testing the comprehension of both active and passive negative sentences, have revealed that dyslexics show a very poor performance when they are asked to interpret negative sentences, whereas age-matched typically developing children accomplish the task almost effortlessly. These results are particularly interesting for two reasons: on the one hand, they corroborate the Two-Step Simulation Hypothesis, claiming that negative sentences are difficult to process, and, on the other hand, they provide new evidence to the hypothesis according to which dyslexia is related to a Verbal Working Memory defici
Chapter 19. Morphological awareness in L2 Italian children with a migrant background
No full textResearch on morphological awareness in bilingual children has generated conflicting evidence, with studies reporting bilingual gains and others finding poorer performance relative to monolinguals. In this study, we explored further this issue by testing 54 school-aged children speaking Italian as an L2 on a broad domain of morphology and by means of nonword tasks, with the aim to reduce potential vocabulary effects on morphological abilities. One group of monolingual Italian-speaking children and two groups of bilingual L2 Italian children (with Romanian and Albanian as L1s) took part in the experiment. Results evidenced similar performances in most tasks, but limited underachievement was found in bilinguals, especially in the Albanian-Italian speaking children. This bilingual gap can be explained by the genealogical and typological distance between the L1 and the target language. Crucially, it disappears once vocabulary and exposure factors are taken into account
The (en)rich(ed) meaning of expletive negation
Full text linkThis contribution addresses the issue of one of the instances of non-standard negation, the so-called expletive negation (EN). Though it discusses data from a variety of languages, it mainly concentrates on Italian, proposing that the behavior of EN in comparative, exclamative and temporal clauses warrants an analysis of EN in terms of an operator of implicature denial. This approach derives the fact that EN is truth-conditionally irrelevant from the fact that the semantics of negation as a truth-value reversal operator is shifted, in the case of EN, to the layer of implicated meaning. The analysis has a number of interesting consequences for the notion of metalinguistic negation. It further derives many of the interpretive effects normally linked to the so-called evaluative analysis of EN, and is compatible with a new set of data showing that EN scopally interacts with other negative elements. Finally, the proposal advanced here has a number of non-trivial implications regarding the relation between morphosyntax and the systems of interpretation, potentially affecting the standard view of language within cognition
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