Lateralization in normal 6-year-olds as related to later reading disability.

The differentiation of lateral preference in hand, eye, ear, and foot was measured in 110 normal Grade 1 children and reading achievement was tested 3 and 5 years later. No support was found for the widely held belief that delays in early lateralization underlie subsequent reading impairment. Paradoxically, boys with serious reading disability showed a strong degree of early lateral concordance. Male, impaired readers displayed a tendency when they were in Grade 1 to be either uniformly right- or left-preferring across all 4 sensory-motor modalities. The results contradict the popular notion that lateral usage emerges from an undifferentiated state in the direction of greater degrees of specialization. Lateralization may be an expression of reflex constraints bound initially to the infant's tonic-neck posture, with later development less reflex-patterned during the acquisition of more sophisticated information-processing strategies. Such an interpretation implies a progressive discontinuity between lateral usage and neuro-maturational processes. Alternatively, the results can be accounted for by (1) a new maturational delay model in which maturation-dependent lateralization proceeds in graduated stages from a highly specialized beginning toward greater levels of neuromotor integration; or (2) a model that maintains the notion of emergent lateralization but in which delays in the lateralization process are actually beneficial to later performance.