Dyslexia is a disorder characterized by severe difficulties with reading, writing, and spelling. It is generally conceptualized as a language disorder. In reality, language is quite complex and multifaceted, and the aim of this special issue is to understand the linguistic aspects of dyslexia from a variety of perspectives.
For about 30 years, researchers have known that a deficit in phonological processing is at the core of dyslexia. Phonological processing refers to a variety of skills, including, but not limited to, the ability to segment speech into smaller units such as syllables and phonemes and the ability to associate sounds with letters. However, difficulties with phonological processing are not the only problem faced by children with dyslexia. The articles in this special issue address various aspects of dyslexia and show the depth and complexity of the language difficulties that accompany dyslexia.
One aspect of language is conversational skills. Smith, Locke, and Farkas have documented some early and subtle language difficulties in children who later develop dyslexia. The children were at high familial risk for dyslexia. When the children were 3 years old, Smith et al. studied the conversational interactions between children and their mothers. The researchers then followed the children into their elementary years. Half of these children showed signs of dyslexia when they were 8 to 9 years old, and half had age-appropriate reading skills. Smith et al. found some interesting differences in early conversational interactions between the children who later became dyslexic and those who did not. The children who later became dyslexic were more likely to wait for adults to speak and were less likely to change the topic of the conversation. These differences probably represent the subtle language difficulties of the children with dyslexia.
Languages have different types of morphology. In English, one important aspect of morphology is endings of words that indicate their grammatical function. For example, ness indicates a noun, ize signifies a verb, and ful signifies an adjective. Siegel's article shows that understanding the morphologic structure of English is related to more accurate reading and spelling skills. Furthermore, individuals with dyslexia had lower scores on tasks-measuring morphologic awareness than normally achieving readers. This relative lack of morphologic awareness may interfere with the speed and accuracy of their reading skills.
As an alphabetic language, English is unique in its degree of irregularity or unpredictability in the correspondence between letters and their sounds. For example, there are 21 ways to represent vowel sounds in English. In the examination of reading skills, it is important to consider other languages that are more regular and transparent. At the other end of the continuum from English is Spanish, which is quite regular and transparent with only 5 vowel sounds. The article by Jimenez, Valle, Rodriquez, Guzman, Diaz, and Ortiz is an investigation of some linguistic aspects of dyslexia in a transparent language.
One of the other cognitive processes implicated in dyslexia is deficits in naming, that is lexical access is slow and sometimes inaccurate. This process is called rapid naming. The study by Jimenez et al. has shown that deficits in rapid naming occur in dyslexia but they are not nearly as important as phonologic deficits.
The article by Molfese, Molfese, Beswick, Jacobi-Vessels, Molfese, Molnar, Wagner, and Haines is an attempt to understand the biological basis of dyslexia. In a study of 3- to 4-year-old preschool children, they found that differences in event-related potentials (ERPs) were related to differences in letter-naming skills. The ERPs were measured during speech perception tasks and the children with poor letter-naming skills showed less sensitive speech discrimination skills than those children with better letter-naming skills.
Dyslexia needs to be understood in a variety of educational contexts. The reality of the educational system in many parts of the world is that children speak one language at home and are educated in school in another language. In the United States, these children are called English language learners (ELL), in Canada they are described as having English as a second language (ESL), and in the United Kingdom they are described as children with English as a second or other language (ESOL). Whatever their designation, when these children experience reading difficulties in school, it is important to ascertain whether or not this is dyslexia or a language problem caused by being educated in a second language.
Townsend and Collins have shown that when assessing children with potential reading difficulties, those who are at risk for reading problems, even if their first language is Spanish, have difficulties very similar to those of children whose first language is English. For the clinician, this finding means that assessment in English (for Spanish-speaking children being educated in English) can be conducted in English and is predictive of later reading skills. Measures of phonological awareness, word recognition, and decoding did successfully discriminate between students who were good readers and those who were at risk for reading disabilities. These findings suggest that it is critically important to assess English learners in the language of instruction. Siegel's study also shows that, with the high-quality instruction, the language and reading skills of children with English as a second language are similar to those of children with English as a first language.
In summary, this series of articles provides some fascinating data on the language deficits associated with dyslexia. For the clinician in the speech and language field, these data suggest children who are at risk. It is also important to study the oral language of children with dyslexia and to understand their conversational skills, their understanding of morphology, their naming speed, and their speech perception and production skills. Finally, the articles of this issue imply that it is important to conduct a thorough assessment of reading skills, and this assessment is valid with both children who have English as a first language and English language learners.
Children who are at risk for reading disorders can be identified early, even before reading instruction starts. The speech and language clinician can play an important role in identifying these children at risk.
Linda S. Siegel, PhD, Issue Editor
Department of Educational and Counselling Psychology, and Special Education, Faculty of Education, University of British Columbia, Vancouver, British Columbia, Canada