On subtypes of developmental dyslexia: Evidence from processing time and accuracy scores.

Abstract

Phonological dyslexics (Ph-DYS) are characterized by a phonological deficit, and surface dyslexics (S-DYS), by an orthographic deficit. Four issues were addressed in this study. First, we determined the proportions of Ph-DYS and S-DYS in a population of French dyslexics by applying the Castles and Coltheart's regression method (1993) to two previously unused diagnostic measures, pseudoword and irregular-word processing time. Thirty-one dyslexics were matched to 19 same-age average readers (10-years-old, CA controls) and to 19 younger children of the same reading level (8-years-old, RL controls). Compared to CA controls, there were more Ph-DYS than S-DYS. Compared to RL controls, there was still a high number of Ph-DYS, whereas the S-DYS profile almost disappeared. Next, we examined the reliability of these subtypes across different measures of phonological and orthographic skills. Compared to RL controls, both groups of dyslexics were found to be impaired only in phonological skills, either in processing time (Ph-DYS) or in accuracy (S-DYS). Then we assessed the moment at which the two dissociated profiles emerged in the course of cognitive development. In order to do so, we examined earlier longitudinal data, collected when the children were 7-and 8-years-old and found that only the S-DYS' orthographic deficit increased with development. Last, we looked at whether the Ph-DYS and S-DYS profiles were associated with other specific cognitive deficits. Specific deficits in phonemic awareness and in phonological short-term memory were found for both Ph-DYS and S-DYS. These data suggested that developmental dyslexia can be largely accounted for by an underlying phonological impairment. FOOTNOTES 1. The 17 lost participants did not differ as to their kindergarten reading level, verbal and nonverbal IQs from the 43 children remaining in the sample.

Reliability and prevalence of an atypical development of phonological skills in French-speaking dyslexics

“…In addition, the length of pseudowords was manipulated, because some apparently inconsistent results on the length effect have been found, even in English (Rack et al, 1992;Van Ijzendoorn & Bus, 1994). Finally, compared to the sample of a previous French study (Sprenger-Charolles et al, 2000), the dyslexics included in the present study were younger and more severely impaired, so that the trends observed in the previous study were expected to be replicated and reinforced. Especially, differences between dyslexics and RL controls were expected to be observed even in regard to accuracy scores, as in studies conducted with English-speaking dyslexics.…”

“…Because of ceiling effects on irregular-word accuracy in CA controls, the regression method was used only for correct-response latencies in one study (Sprenger-Charolles et al, 2000). In sharp contrast with the results obtained with the classical method, the regression method pointed out a high percentage of soft-dissociated profiles, and a low percentage of mixed profiles.…”

“…However, this deficit mainly shows up in pseudoword reading accuracy scores in English (Rack et al, 1992;Van Ijzendoorn & Bus, 1994). Alternatively, in transparent orthographies, this deficit mainly shows up in pseudoword reading speed (in Spanish: Jimenez-Gonzalez & Valle, 2000;in French: Casalis, 1995;Grainger, Bouttevin, Truc, Bastien, & Ziegler, 2003;Sprenger-Charolles, Colé, Lacert, & Serniclaes, 2000).…”

“…More recently, five multiple-case studies were carried out, three with English-speaking dyslexics (Castles & Coltheart, 1993;Manis, Seidenberg, Doi, McBride-Chang, & Peterson, 1996;Stanovich, Siegel, & Gottardo, 1997) 1 and two with French-speaking dyslexics (Génard, Mousty, Content, Alegria, Leybaert, & Morais, 1998;Sprenger-Charolles et al, 2000). Two methods were used to analyze the results: the classical method and the regression method.…”

“…Dyslexics whose scores are outside the confidence intervals in both cases have a mixed profile. In all but one these studies, the sole indicator of reading efficiency was accuracy; in one study, correct-response latency was also taken into account (Sprenger-Charolles et al, 2000).…”