The questions of whether chronically dyslexic adolescent suffer any deficits of simple language stimulus processing or are less left hemisphere dominant than normal reading controls were addressed. The dyslexics were chosen for clarity of their specific reading problem and were older than dyslexics previously studied with lateralizing tests. Tasks administered in Experiment I were unilateral and bilateral tachistoscopic work recognitions and a tachistoscopic recognition report-time task for single lateralized letter stimuli. Experiment II, conducted a year later, readministered these tasks with modifications, and added dichotic digits and motor reaction time-stimulus detection tasks. It was concluded that right handed, chronic dyslexics: (1) possess left hemisphere language specialization; (2) show normal interhemispheric processing delays for single letter stimuli; (3) are, unlike nondyslexis but equally poor-reading Ss, clearly impaired in their efficiency of visual and auditory processing of simple language stimuli; (4) possess clear auditory memory deficits for verbal material; and (5) may possess an additional deficit of left hemisphere visual association area function.
Filbey and Gazzaniga (1969) found simple dot-present or -absent reports averaged 35 ms slower for the left than for the right visual field. Other data suggests that verbal processing efficiency differences between the cerebral hemispheres, rather than transcallosal transfer time alone, must be tapped to obtain half-field differences as large as 35 ms. Three experiments were conducted. The first failed to show any half-field differences in vocal RT for dot detection; the second replicated previous reports of significant right field superiority of vocal RT to letter stimuli for right handers, and also showed a substantially smaller half-field difference for left handers; the third experiment, utilizing the fixation control procedure of the second experiment, again failed to show half-field differences for the dot detection paradigm. Differences between the Filbey and Gazzaniga and present results probably reflect important procedural differences. We conclude that transcallosal transfer time for simple dot information is much smaller than assumed by Filbey and Gazzaniga and that the letter report-time task taps hemispheric asymmetries of verbal processing efficiency.
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