Timing analysis of coding and articulation processes in dyslexia.
Several investigators have found that the time required to perform serial naming tasks is a good predictor of dyslexia in children. Protracted overall time scores, such as are reported for the Rapid Automatized Naming (RAN) test of Denckla and Rudel, are, by themselves, insufficient to determine the extent to which the performance deficit is cognitive in nature, or is the articulatory consequence of an inability master the quickly changing acoustic formant patterns associated with consonants, as proposed by Tallal. We administered the RAN test to matched groups of dyslexic and normal control children, aged 8 to 11 years. Measurement of speech signal durations was performed by computer. We applied the Gould and Boies algorithm for extracting cognitive preparation time to these data, resulting in a partition of overall RAN test score into coding time and articulation time components. Differential performances between the groups on RAN subtests were examined for effects of postvocalic consonants and semantic load. It was found that both vocalization time and pause time means were significantly longer for the dyslexics on each of the four RAN subtests: objects, colors, numbers, letters. The Gould and Boies analysis showed very little preparation time during speech in both groups, attributing virtually all coding time to pauses, although reanalysis suggested somewhat less. Increased vowel length among the dyslexics occurred on all subtests, but was not maximized on subtests with more numerous postvocalic consonants. Vowel time differences between groups accounted for nearly all of the differences in vocalization time. Profiles were constructed on speech measures which, for each subtest, correctly identified each subject with his group. On the letters subtest it was found that vowel duration alone achieved a perfect discrimination between the dyslexic and control subjects.