Comparing the phonological and double deficit hypotheses for developmentaldyslexia

This study tested the predictions of the phonological and double deficit hy potheses by experimentally examining speech perception, phoneme awareness, lexical retrieval (serial and discrete), articulatory speed, and verbal STM in school age child (N = 35) and adolescent (N = 36) dyslexics, and both c hronological age (CA) and reading age (RA) controls. The results confirmed the findings of previous studies of a deficit in phoneme awareness in devel opmental dyslexia. At both age levels, dyslexics performed significantly mo re poorly than both their CA and RA controls. Although deficits in the othe r processes investigated, particularly in rapid serial naming, were also ap parent, they were not as clear-cut as the deficit in phoneme awareness. In general, definite evidence of a deficit in rapid serial naming was limited to the more severely impaired dyslexics. Furthermore, although rapid serial naming contributed independent variation to various literacy skills, its c ontribution was modest relative to the contribution of phoneme awareness, r egardless of whether the literacy skill relied more or less heavily on phon ological or orthographic coding skills. Further analyses suggested that var iation in rapid serial skill is particularly important for fluent reading o f text, whereas phoneme awareness is particularly important for the develop ment of the ability to read by phonologically recoding letters or groups of letters in words into their phonological codes. This explains the relative ly strong contribution of phoneme awareness to reading and spelling ability in general. In sum, the phonological hypothesis offers a more parsimonious account of the present results than the double deficit hypothesis.