Dyslexia: Neuronal, Cognitive and Linguistic Aspects

Proceedings of an International Symposium Held at the Wenner-Gren Center, Stockholm, June 3-4, 1980

Yngve Zotterman

• Publisher: Pergamon
• Year: 2013
• Print ISBN: 9780080268637
• eBook ISBN: 9781483148052
• Topic: Medicine
• Subtopic: Diseases & Allergies

Dyslexia: Neuronal, Cognitive & Linguistic Aspects focuses on the desire of scholars to identify the etiology of dyslexia and how it affects the ability of children to read and write. This book features the works of authors who have conducted extensive research on dyslexia. In the neuronal aspect of defining the origin of dyslexia, the selection commences by defining the neuroanatomical features of language and dyslexia. This discussion is followed by a tracking of the sections of the brain that are involved in this kind of deficiency. In the cognitive facet, the selection features discussion on how the right hemisphere functions relative to the ability to read. This topic is followed by several observations, which point out that the right hemisphere has no direct influence on a person's ability to read; however, it is stressed that this part of the brain has visuo-spatial capabilities. The discussion is followed by a presentation of opthalmological findings among children with learning difficulties. The book then proceeds to the relationship of dyslexia with visual problems and linguistic awareness. In this regard, questions on the ability of children to be able to read prior and during their school years are raised. The selection ends with a discussion on how to treat dyslexia through the use of computers. This book is a great source of information for neurophysiologists, psychophysiologists, ophthalmologists, and teachers who are interested in helping children learn to read and write.

III

Cognitive Aspects

Outline

Chapter 7: READING BY THE DISCONNECTED RIGHT HEMISPHERE: AN APHASIOLOGICAL PERSPECTIVE

Chapter 8: THE RELATIONSHIP BETWEEN ICONIC PERSISTENCE AND READING DISABILITIES

Chapter 9: DISCUSSION

Chapter 10: OPHTHALMOLOGICAL FINDINGS AND CONTRAST SENSITIVITY IN CHILDREN WITH READING DIFFICULTIES

Chapter 11: DISCUSSION

READING BY THE DISCONNECTED RIGHT HEMISPHERE: AN APHASIOLOGICAL PERSPECTIVE

E. ZAIDEL, Department of Psychology, University of California at Los Angeles, California, and Division of Biology, California Institute of Technology, Pasadena, California, USA

Summary

I Classical clinical neurology rarely recognizes any reading ability in the right hemisphere (RH) of right handed adults. In particular, the syndrome of alexia without agraphia highlights the failure of the RH to read when the left angular gyrus is disconnected from visual stimuli. I suggest that the disconnection account of alexia without agraphia is inadequate. Following cerebral commissurotomy (split brain), the disconnected RHs seem mute but may have some capacity for phonological encoding as shown by recognition of pictures with homonymous or rhyming names. But the extent of phonological encoding in these RHs is insufficient to translate orthography into sound during RH reading.

II Such phonological encoding can also be preserved in acquired expressive aphasia in the absence of naming. Reading in the disconnected hemispheres of two complete commissurotomy patients and in the isolated hemispheres of three hemispherectomy patients was assessed with reading subtests from common aphasia batteries. The results show a pattern of reading in the disconnected RHs that is consistent with the hypothesis that the RH supports reading in many alexic aphasics. In particular, the disconnected RHs seem to read words “ideographically”, without intermediate translation of orthography into sound.

III Reading without phonological recoding, as well as a preponderance of semantic errors in RH misreadings, both suggest that the RH is particularly likely to support reading in cases of acquired “deep dyslexia”. Clinical testing of alexia should incorporate tasks requiring pointing to multiple choice pictures rather than speech responses, in the manner used for RH testing.

IV Together with data from reading following hemispherectomy and from hemifield studies in normal subjects, the split brain results suggest that interhemispheric interaction with the LH facilitates the involvement of the normal RH in reading beyond what is apparent in the disconnected RH. Congenital failure of such interhemispheric interaction may result in certain forms of developmental dyslexia.

KEYWORDS

Reading

hemispheric specialization

alexia

aphasia

commissurotomy

hemispherectomy

right hemisphere language

phonological encoding

grapheme-to-phoneme translation

OUTLINE

1 Introduction

The neurological tradition

Acquired alexia

2 Language in the disconnected right hemisphere

Right hemisphere speech

Phonological encoding by the right hemisphere Aphasia

“Ideographic” reading by the right hemisphere

Aphasic profiles of right hemisphere reading

The Minnesota and Boston aphasia batteries

The Western Aphasia Battery

Sklar Aphasia Scale

Word categories

Actions

The disconnected right hemisphere as a deep dyslexic

3 Reading following hemispherectomy for postinfantile lesions

Dominant hemispherectomy

Nondominant hemispherectomy

Right hemispherectomy during reading acquisition

Right hemispherectomy following reading acquisition

4 Interhemispheric dynamics in reading

Variability in commissurotomy data

Right hemisphere speech and reading in aphasia

Role of the right hemisphere in normal reading

INTRODUCTION

The Neurological Tradition

The concept of left hemisphere specialization for processing linguistic functions, at least in right handed adult males, originates with the talk of the French physician Marc Dax to a French medical society in 1836 (Joynt and Benton, 1964), and with the seminal papers of the French anthropologist and pathologist Paul Broca in 1865 and of the German neurologist Carl Wernicke in 1874. Dax linked loss of speech to left hemisphere (LH) lesions because of its association with right hemiplegia; Broca associated speech disorders with lesions of the third left frontal convolution; and Wernicke further ascribed auditory language comprehension loss to damage in the posterior first and second left temporal convolutions (cf. Bogen and Bogen, 1976). It is noteworthy that these views developed in the absence of evidence for structural differences between the hemispheres.

The concept of LH specialization for language was boldly extended to the doctrine of LH dominance in general, largely by Liepmann who argued in 1908 that the LH was specialized for praxis (motor control). This view required the postulation of cross callosal mediation of motor commands from the LH to the left hand. The concept of LH specialization for language implied an absence of RH competence for either speech, reading, or auditory comprehension. Thus, the symptoms of Dejerine’s famous 1892 patient who had alexia without agraphia, were subsequently attributed to interruption of visual callosal fibers from the right to the left hemisphere due to a left occipital lesion also causing a right homonymous hemianopsia. Because of the left occipital lesion the patient could only see with his RH; he could not read because his seeing RH was disconnected from the reading centers in the LH.

Such an explanation, of course, presupposes that the seeing RH cannot read. This assumption is contradicted by data to be presented in this paper, showing that the disconnected RH has some reading ability. Tests of reading in patients having alexia without agraphia have commonly not been adequate. An adequate test would involve multiple choice pointing or other nonverbal responses in tasks requiring matching of printed words and their pictured object referents, matching of printed and spoken words, and lexical decision tasks – judgements about “wordness” of letter strings. In particular, one should test for the presence of automatic unconscious components of reading, as in facilitation of lexical decision tasks, where a quickly flashed word whose presence can be ignored or even denied, nonetheless speeds up or improves the decision as to whether a semantically related subsequent letter string is a word or not.

The doctorines of LH dominance and callosal mediation were revived by Norman Geschwind in the 1960’s (Geschwind, 1965) with an emphasis on localization and disconnection syndromes in aphasiology.

Acquired Alexia

For the purpose of this paper, I consider two distinct senses in which the RH appears to be “word blind”, i.e. unable to read even single words. First, there are LH lesions responsible for the agraphic varieties of acquired alexia: alexia with associated loss of auditory comprehension, due to posterior LH lesions; alexia with agraphia but little if any speech defect, due to lesions of the left angular gyrus; and frontal alexia associated with relative preservation of semantic reference and relative loss of grammar and phonology (Benson, 1977). Lesions in homologous regions of the RH do not usually result in reading disorders except, perhaps, in impaired prosody. In fact, as Benson (1980) notes, alexia appears to be a stronger lateralizing sign than speech disorders; clinically, the presence of alexia almost invariably indicates dominant (left) hemisphere abnormality. (However, alexic symptoms may occur as part of the unilateral neglect syndrome following RH lesions). While these clinical observations allow us to infer LH specialization for reading, they do not necessarily imply complete RH inability to read. It is possible that cross-callosal pathological inhibition of the healthy RH by the diseased LH tissue is a factor, thus preventing the residual RH competence from expressing itself.

Second, there is yet another variety of acquired alexia, alexia without agraphia, that explicitly denies the RH any positive reading competence. The syndrome was first described in 1877 by Kussmaul who coined the term “word blindness” (Benson, 1980). In 1892 Dejerine provided a detailed clinical evaluation, definitive postmor...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• LIST OF PARTICIPANTS
• EDITOR’S PREFACE
• OPENING ADDRESS
• INTRODUCTORY REMARKS
• I: Structural and Functional Background
• II: Cortical Information Systems
• III: Cognitive Aspects
• IV: Clinical Experience and Pedagogic Aspects
• Chapter 10: FINAL DISCUSSION
• Chapter 11: ADDENDUM: A METHOD TO STUDY AND TREAT DYSLEXIA BY PRODUCING STANDARDIZED ICON-PICTURES FROM FLASHING WORDS ON A COMPUTER SCREEN FROM FLASHING WORDS ON A COMPUTER SCREEN
• INDEX