Attentional control over language lateralization in dyslexic children: deficit or delay?

Two previous verbal dichotic studies by Kershner and Morton (Neuropsychologia 28, 181-198, 1990) using the forced-attention methodology (Bryden, Strategies of Information Processing, Academic Press, London, 1978) demonstrated that the order in which the ears were monitored (LE first or RE first) determined whether learning disabled children compared to age-matched nondisabled children were more weakly or strongly lateralized. The same technique was used with the addition of controls for lateral head and eye movements, specific diagnostic criteria to include only phonological dyslexics, IQ and reading level. Dyslexic vs age-matched comparisons replicated the previous studies. The dyslexics produced a weaker REA in the LE first order but a greater number of subjects with a REA in the RE first order. Reading-matched comparisons suggested that the order-specific reduced REA in the dyslexics may reflect a causal deficit of the disorder, whereas the order-specific increase in the number of dyslexic subjects with a REA was no different than the reading-matched group, implicating a developmental delay. The results suggest that children with dyslexia may suffer from a primary attentional impairment in altering the REA. This implicates an underlying difficulty of flexible verbal processing in response to the rapidly changing cognitive requirements of reading.