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Is there something you have always wanted to know about language? We might have an answer! On this page we answer questions about various aspects of language asked by people outside of the language researcher community.

How does dyslexia arise?

When a child has significant difficulties in learning to read and/or spell despite normal general intelligence and overall sensory abilities, then he or she may be diagnosed with developmental dyslexia. This condition was first described in the 1890's and referred to as 'congenital word blindness', because it was thought to result from problems with processing of visual symbols. Over the years it has become clear that visual deficits are not the core feature for most people with dyslexia. In many cases, it seems that subtle underlying difficulties with aspects of language could be contributing. To learn to read, a child needs to understand the way that words are made up by their individual units (phonemes), and must become adept at matching those phonemes to arbitrary written symbols (graphemes). Although the overall language proficiency of people with dyslexia usually appears normal, they often perform poorly on tests that involve manipulations of phonemes and processing of phonology, even when this does not involve any reading or writing.

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Since dyslexia is defined as a failure to read, without being explained by an obvious known cause, it is possible that this is not one single syndrome, but instead represents a cluster of different disorders, involving distinct mechanisms. However, it has proved hard to clearly separate dyslexia out into subtypes. Studies have uncovered quite a few convincing behavioural markers (not only phonological deficits) that tend to be associated with the reading problems, and there is a lot of debate about how these features fit together into a coherent account. To give just one example, many people with dyslexia are less accurate when asked to rapidly name a visually-presented series of objects or colours. Some researchers now believe that dyslexia results from the convergence of several different cognitive deficits, co-occurring in the same person.

It is well established that dyslexia clusters in families and that inherited factors must play a substantial role in susceptibility. Nevertheless, there is no doubt that the genetic basis is complex and heterogeneous, involving multiple different genes of small effect size, interacting with the environment. Genetic mapping efforts have already enabled researchers to pinpoint a number of interesting candidate genes, such as DYX1C1, KIAA0319, DCDC2, and ROBO1, and with dramatic advances in DNA sequencing technology there is much promise for discovering others in the coming years. The neurobiological mechanisms that go awry in dyslexia are largely unknown. A prominent theory posits disruptions of a process in early development, a process in which brain cells move towards their final locations, known as neuronal migration. Indirect supporting evidence for this hypothesis comes from studies of post-mortem brain material in humans and investigations of functions of some candidate genes in rats. But there are still many open questions that need to be answered before we can fully understand the causal mechanisms that lead to this elusive syndrome.

by Simon Fisher

 Further reading:

Carrion-Castillo, A., Franke, B., & Fisher, S. E. (2013). Molecular genetics of dyslexia: an overview. Dyslexia, 19, 214–240. (link)

Demonet, J. F., Taylor, M. J., & Chaix, Y. (2004). Developmental dyslexia. Lancet, 63, 1451–1460 (link)

Fisher, S. E. & Francks, C. (2006). Genes, cognition and dyslexia: learning to read the genome. Trends in Cognitive Science, 10, 250-257.(link)

About MPI

This is the MPI

The Max Planck Institute for Psycholinguistics is an institute of the German Max Planck Society. Our mission is to undertake basic research into the psychological,social and biological foundations of language. The goal is to understand how our minds and brains process language, how language interacts with other aspects of mind, and how we can learn languages of quite different types.

The institute is situated on the campus of the Radboud University. We participate in the Donders Institute for Brain, Cognition and Behaviour, and have particularly close ties to that institute's Centre for Cognitive Neuroimaging. We also participate in the Centre for Language Studies. A joint graduate school, the IMPRS in Language Sciences, links the Donders Institute, the CLS and the MPI.

 
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This project was coordinated by:

Katrien Segaert 
Katerina Kucera
Judith Holler

Sean Roberts
Agnieszka Konopka
Gwilym Lockwood
Elma Hilbrink
Joost Rommers
Mark Dingemanse
Connie de Vos