In this paper we critically examine theoretical issues and practical consequences of including IQ in the definition of dyslexia. According to the discrepancy criterion individuals are classified as dyslexic if their reading skills are below what would be expected from their IQ scores. However, we argue that intelligence is a fuzzy concept and that there is no clear causal relationship between intelligence level and word decoding skills. Also, high and low IQ poor readers show the same reading performance patterns, indicating that both groups might benefit from the same remedial activities. Evidence for the critical role of phonological skills in dyslexia is presented and a more recent definition of dyslexia is discussed in relation to these findings. Finally, two alternative, more outcome-based classifications of poor readers are suggested and some critical consequences for individual interventions are outlined.

Most of the research on the acquisition of word-decoding skills has almost exclusively focused on the ability to read words in isolation. The purpose of this article is to extend our knowledge to the independent role of phonological and orthographic word-decoding skills in the reading tasks which children encounter in school. The data were quite consistent with the general core of models suggesting that children first become proficient in phonological decoding then gradually shift towards a more direct orthographic-decoding strategy. As such, these findings have helped to generalize models of the acquisition of word-decoding skills to reading comprehension.

Schacter et al. (1990) found support for a functional dissociation between visual and auditory priming effects in a letter-by-letter reader. Their conclusions were based on the perceptual representation systems framework, suggesting that visual priming is mediated by a visual word form system separate from an auditory word form system responsible for auditory priming. This article focuses on visual and auditory priming effects exhibited by poor readers with phonological or surface subtypes of reading disability. The phonological type of reading disability was defined as an impairment in phonological word decoding, whereas the surface type of reading disability was defined as an impairment in orthographic word decoding. The results demonstrated a double dissociation, such that poor readers with a surface type of reading disability produced more auditory than visual priming, whereas poor readers with a phonological type of reading disability showed more visual than auditory priming. The majority of children with reading disabilities showed weaknesses in both orthographic and phonological word decoding and, importantly, low levels of priming effects for both visually and auditorily presented materials. Finally, age-matched normal readers showed significant priming effects for both visual and auditory presented words. These findings support the assumption that both orthographic and phonological skills can be simultaneously impaired and that a dual-route model for the acquisition of word decoding skills might be the most appropriate framework to describe different subtypes of reading disabilities.

Subgroups of children with reading disabilities were identified by using the regression method introduced by Castles and Coltheart (1993). Children who were poor in phonological, compared to orthographic, word decoding were identified as phonological-type participants, and children who were poor in orthographic, compared to phonological, decoding were identified as surface-type participants. The results replicated previous findings reported that if categorizations are based on comparisons with younger reading-level-matched controls instead of age-matched controls, the number of surface-type children is significantly reduced. Surface-type children performed below the other groups on most cognitive measures and reported that there were fewer books in their homes, and phonological-type children showed a specific deficit in phonological word decoding. The results provided additional support for the hypothesis that the surface type of reading disability can be characterized as a general developmental delay.

n a longitudinal intervention study, 33 Swedish poor readers in Grade 4 received phonological awareness instruction over 1 year. Three control groups were included in the study: Grade 4 controls, Grade 2 controls (both comparable in reading skill) and normal readers. The results showed that the phonological training group made the most progress in phonological awareness but did not improve their reading skills any more than the controls. However, a re-analysis of the results revealed important individual differences within the phonological training group. Some children improved their reading ability considerably, while others seemed resistant to the intervention. One critical difference between improved and resistant readers was identified. For the improved readers, both orthographic and phonological word decoding predicted text reading performance. For the resistant readers, only orthographic decoding skills predicted text reading before, during and after the intervention, in spite of a steady increase in phonological awareness.