Archive for the 'Theory' Category

Visual differences are a consequence, not a cause, of dyslexia

In an article to appear 10 July 2013 in Neuron, Olumide Olulade, Eileen Napoliello, and Guinevere Eden present a series of studies that greatly help educators, psychologists, neurologists, and others understand the relationship between visual deficits and dyslexia. Although most people interested in reading have understood that problems with phonological processes undergird dyslexia, personal accounts of those with dyslexia and some anomalous evidence about the visual cortex and the performance of individuals with dyslexia on certain visual tasks kept the possibility of a visual component open to debate. Professor Eden’s group devised studies and collected the data that shed light on these issues.

In a nutshell, in their first study, Eden’s team found the same results that others had found: When their participants with dyslexia were compared to similar aged children, they showed certain deficits in visual processing associated with a particular part of the brain shown by fMRI. However, when their participants were compared with younger children of like reading ability, there are no deficits in the visual performance; so, these children must not have had the visual problems all along. In their third study, the researchers provided even stronger evidence: The provided powerful remedial reading instruction to their participants and they observed not only improved reading outcomes, but they also found that the students had improved performance on the visual tasks as reflected in fMRI. (Click the accompanying image for a movie of Professors Eden and Olulade explaining the experiments.)

Here is the abstract:

Developmental dyslexia is a reading disorder, yet deficits also manifest in the magnocellular-domi- nated dorsal visual system. Uncertainty about whether visual deficits are causal or consequential to reading disability encumbers accurate identifica- tion and appropriate treatment of this common learning disability. Using fMRI, we demonstrate in typical readers a relationship between reading ability and activity in area V5/MT during visual motion pro- cessing and, as expected, also found lower V5/MT activity for dyslexic children compared to age- matched controls. However, when dyslexics were matched to younger controls on reading ability, no differences emerged, suggesting that weakness in V5/MT may not be causal to dyslexia. To further test for causality, dyslexics underwent a phonolog- ical-based reading intervention. Surprisingly, V5/MT activity increased along with intervention-driven reading gains, demonstrating that activity here is mobilized through reading. Our results provide strong evidence that visual magnocellular dysfunc- tion is not causal to dyslexia but may instead be consequential to impoverished reading.

Olulade, O. A., Napoliello, E. M., & Eden, G. F. (2013). Abnormal visual motion processing is not a cause of dyslexia. Neuron, 79, 1-11. doi:10.1016/j.neuron.2013.05.002

Subtyping LD

Have you been hearing a lot about subtypes of LD lately? Perhaps it’s just that I’ve been especially alert to it, but it seems I’ve heard a lot of mentions about subtypes of Learning Disabilities in the last few weeks. I want to write a longer, more thorough discussion of the topic, but I’ve found myself repeating a few foundational comments, so I thought I ought to post them here and let others have a go at them.

First, the idea of subtypes of LD is essentially a given. It has to do with the heterogeneity of LD. Because LD is essentially an umbrella category for a diverse array of learning disabilities (note the plural), there are bound to be subgroups. Some students will have problems primarily with reading, some primarily with arithmetic and mathematics, some with writing, others with combinations of these. That makes for lots of subgroups right there. That is, one could start with dyslexia, dyscalculia, and dysgraphia!
Continue reading ‘Subtyping LD’

Procedural learning theory of dyslexia and dysgraphia

In “Dyslexia, Dysgraphia, Procedural Learning and the Cerebellum,” Roderick Nicolson and Angela Fawcett present a fascinating and, to me, strong argument for unifying theoretical views of dyslexia and dysgraphia. To be sure, their analysis is preliminary and basic, but my first read left me feeling as if they’d hit lots of good points. They’ve emphasized impairment of automatic procedural learning in the cerebellum at the level of neural circuits, but in dysgraphia the problems are with motor circuits and in dyslexia they are in the language circuits. In developing their case, they integrate a broad range of neurological and psychological research.

In this review we focus on the developmental disorders of dyslexia (a disorder of reading) and dysgraphia (a disorder of writing), considering their commonalities and differences with a view to reflecting on the theoretical implications. Interest in dysgraphia was stimulated by the distinction between phonological and surface dyslexia (Castles and Coltheart, 1993), which claimed that orthographic problems (spelling) were separable from phonological reading problems. While this distinction has received mixed support ([Snowling et al., 1996] and [Stanovich et al., 1997]) it led to a fruitful analysis not only of the underlying causes of orthographic difficulties, but also to the widespread recognition of developmental difficulties in handwriting control ([Deuel, 1995], [Manis et al., 1996] and Sprenger-Charolles et al., 2000 L. Sprenger-Charolles, P. Cole, P. Lacert and W. Serniclaes, On subtypes of developmental dyslexia: Evidence from processing time and accuracy scores, Canadian Journal of Experimental Psychology-Revue Canadienne De Psychologie Experimentale 54 (2000), pp. 87–104. Abstract | Full Text via CrossRef[Sprenger-Charolles et al., 2000]). The result of this theoretical and empirical progress is that there are two usages of the term dysgraphia. One takes dysgraphia to refer to errors of writing that are analogous to errors in reading (e.g., surface, phonological or deep dysgraphia corresponding to surface, phonological and deep dyslexia), the other relating to difficulties in handwriting control. Furthermore, despite these attempts at differentiation, there remains some controversy in the literature as to whether motor difficulties in handwriting should be subsumed under the label dyslexia.
Continue reading ‘Procedural learning theory of dyslexia and dysgraphia’

Helmer Myklebust

Helmer R. Myklebust, one of the pioneering figures in Learning Disabilities, died 26 February 2008. Predicated on his work on differentiating among speech disorders, Professor Myklebust emphasized the language-based aspects of Learning Disabilities. He theorized that there were different types of Learning Disabilities and that these types required different treatments. Throughout his career, Professor Myklebust promoted empirical study of language disorders and Learning Disabilities.

Professor Myklebust came to the study of Learning Disabilities after extensive work in hearing and speech disorders. In the 1940s he studied deafness and in the 1950s he focused on aphasia. In 1967, with his collaborator Doris Johnson, Professor Myklebust published one of the first books focused on Learning Disabilities: Learning Disabilities: Educational Principles and Remedial Approaches and later he edited a series of volumes presenting research and theory about Learning Disabilities under the title Progress in Learning Disabilities.

Professor Myklebust sought to differentiate among different variants of Learning Disabilities. He thought that Learning Disabilities could be separated into disorders of auditory language (generalized auditory disorders, auditory receptive disorders, and auditory expressive disorders), disorders of written language (auditory dyslexia, visual dyslexia, and written expression), disorders of arithmetic, and disorders of a non-verbal type. Professor Myklebust proposed that the problems children experienced were a consequence of difficulties in “interneurosensory learning.”

Professor Myklebust, who was born 2 august 1910 in Lester (IA, US), was among a small group of educators and psychologists who generally credited with founding the study of Learning Disabilities. Along with Samuel Kirk, William Cruickshank, Marianne Frostig, Newell Kephart, and perhaps a few others, Myklebust pursued the recognition of the difficulties experienced by these children and their families.

He received a bachelors degree from Augustana College, a masters degrees from Gallaudet College and Temple University, and a doctoral degree from Rutgers University. He taught and conducted research at several institutions, including Northern Illinois University; Northwestern University, where he spent most of his career and where he founded the Children’s Hearing and Aphasia Clinic; University of Illinois, Chicago. Memorial services were held 8 March.

Johnson, D. J., & Myklebust, H. (1967). Learning disabilities: Educational principles and remedial approaches. NY: Grune & Stratton.

Myklebust, H. (1954). Auditory disorders in children: A manual for differential diagnosis. NY: Grune & Stratton.

Myklebust, H. (Ed.). (1968-1975). Progress in learning disabilities (vols. 1-5). NY: Grune & Stratton.

I am late in publishing this note; thanks to Hal McGrady for alerting me to the death of this giant figure in the history or LD.