Authors: Cristina Romani, Anna Maria Di Betta, Effie Tsouknida & Andrew Olson.

Article: Lexical and nonlexical processing in developmental dyslexia: A case for different resources and different impairments.

Publication: Cognitive Neuropsychology (Taylor and Francis). 25:6, 798-830, 2008 | DOI: 10.1080/02643290802347183

[Full Text]

In a group of adult dyslexics word reading and, especially, word spelling are predicted more by what we have called lexical learning (tapped by a paired-associate task with pictures and written nonwords) than by phonological skills. Nonword reading and spelling, instead, are not associated with this task but they are predicted by phonological tasks. Consistently, surface and phonological dyslexics show opposite profiles on lexical learning and phonological tasks. The phonological dyslexics are more impaired on the phonological tasks, while the surface dyslexics are equally or more impaired on the lexical learning tasks. Finally, orthographic lexical learning explains more variation in spelling than in reading, and subtyping based on spelling returns more interpretable results than that based on reading. These results suggest that the quality of lexical representations is crucial to adult literacy skills. This is best measured by spelling and best predicted by a task of lexical learning. We hypothesize that lexical learning taps a uniquely human capacity to form new representations by recombining the units of a restricted set.

Tagged as: adult dyslexia, nonword reading, orthographic processing, phonological processing, and surface dyslexia


Cristina Romani, Anna Maria Di Betta, Effie Tsouknida & Andrew Olson (2008) Lexical and nonlexical processing in developmental dyslexia: A case for different resources and different impairments, Cognitive Neuropsychology, 25:6, 798-830, DOI: 10.1080/02643290802347183

Excerpts from Full Text / Notes:
In our dyslexic adult group, the phonological factor, which shows such strong association with reading and spelling in children, shows no association at all with either word spelling or word reading accuracy, consistent with the hypothesis of a diminished role of phonological skills with development. Instead, the phonological factor continues to be strongly associated with nonword spelling and nonword reading speed and to a lesser extent with word reading speed
We found that, in a group of adult dyslexics, scores on our task of written lexical learning were more strongly related to real-word reading/spelling than to nonword reading/spelling. Conversely, sublexical phonological processing skills such as those measured by short-term memory tasks, phonological awareness tasks, and our CR index were more strongly related to nonword reading/ spelling. Furthermore, when we divided our dyslexic group into surface and phonological subgroups, we found that the surface group performed: (a)normally and as well as the phonological group on tasks of general ability (performance IQ, vocabulary, similarities, Rey words); (b) poorly, but better than the phonological group on phonological tasks; and (c) poorly and as bad or worse than the phonological group on the lexical learning tasks. These results indicate that the lexical learning impairment of the surface dyslexics cannot solely be attributed to phonological difficulties.
Our results paint a consistent picture. Nonlexical processing was strongly and selectively associated with phonological skills, while lexical processing was mainly associated with lexical learning. We need to refer to both skills to explain the different forms and the severity of impairments seen in adult dyslexics.

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