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A group of 39 persons (20 male and 19 female, 11.0 to 32.5 yr.) with developmental dyslexia and 42 controls (21 male and 21 female, 11.2 to 32.3 years) were compared on computerized tests of sight word reading, nonword decoding, and spelling recognition. The subjects with developmental dyslexia performed significantly slower and less accurately than controls on all tasks. Further, the effect size of the group differences was larger for the older group. Within-group analyses showed a significant difference by age group on accuracy. Only the control group showed a significant age difference between groups on response time. Mean accuracy and response times for the reading-disabled subjects resembled shifted versions of the control group means. These results agree with previous reports that phonological deficits persist for reading-disabled adults and suggest a test of whether the discrepancy between reading-disabled and typically achieving readers may actually increase across age groups.

The role of auditory temporal processing in reading and spelling was investigated in a sample of 30 children and one of 31 adults, using a gap-detection task with nonspeech stimuli. There was no evidence for a relationship between reading and spelling disability (dyslexia) and the gap-detection threshold. The results were discussed regarding the relevance for the popular hypothesis of an auditory temporal processing deficit underlying dyslexia.

A peripheral retina, photoreceptor, or transient visual-system deficit has been suggested as a basis for dyslexia. We performed dark adaptation using a Goldmann-Weekers adaptometer on 41 dyslexic readers subjected to the Irlen Differential Perceptual Schedule for the Scotopic Sensitivity Syndrome and on 23 volunteers of normal reading ability, all aged between 10 and 20 years. 12 of the 41 disabled readers examined had abnormally poor dark adaptation at peripheral retinal locations consistent with a rod processing-system deficit.

Recently Stuart and Lovegrove questioned the receptor hypothesis of Grosser and Spafford which these authors used to account for the findings that dyslexic individuals have superior peripheral color discrimination to normal readers but also have poorer peripheral brightness discrimination than normal readers. Stuart and Lovegrove hypothesized that dyslexics instead have an impaired transient visual system. The receptor hypothesis is an attempt by Grosser and Spafford to link the functioning of the rods and cones to transient and sustained visual system functioning in a more specific manner than has been tried heretofore by suggesting that, while the parvocellular system is almost entirely fed by cones, both kinds of receptors drive magnocellular cells (but with the rapid onset of early transient system responding being due to the highly light sensitive rods). The rods are proposed to be the receptors initiating the rapid onset of responding in the magnocellular, transient pathway. In dyslexic individuals, they maintain, there are relatively fewer rods to provide for the rapid onset of transient system responses, resulting in a diminished capacity of the transient system to inhibit sustained system activity (as occurs with normal readers). Their receptor hypothesis supplements the concept of transient-vs-sustained system differences.

A group of 7 dyslexic students and 8 nondyslexic students matched for age and IQ were tested on recognition of computer-presented voices and faces. Although face recognition showed a ceiling effect which prevented any solid conclusions being drawn from this task, the dyslexic group were significantly impaired on the recognition of voices.

In a previously reported longitudinal study of reversal errors for static and kinetic written symbols we found no compelling support for their academic importance in kindergarten (n=201), Grade 1 (n=156), or Grade 2 (n=129); however, for Grade 3 (n=105), kinetic reversals became a significant predictor of tested reading achievement. If reliable, this finding might have implications for the identification of children with long-term reading impairment.

The present study tested the hypothesis that from the ability of dyslexics to read peripheral letters one may infer the presence of cones, those visual receptors specialized for acuity, in the peripheral retina. The cones are also the receptors for color discriminations. The method of retinal perimetry was used to map color-sensitive zones of the retina for 14 dyslexic and 14 control subjects. A statistically significant difference showed that the 14 dyslexis reported colors at more peripheral positions than did the 14 normal readers. These data are consistent with the premise that dyslexics have an anomalous distribution of retinal receptors. These findings perhaps may help to explain the erratic eye movements of some dyslexics. It is suggested that retinal perimetry might be one component of a diagnostic battery for the differential diagnosis of dyslexics.

To measure the ocular fixation and sequential scanning dysfunction assumed responsible for the visual reading symptoms which characterize dyslexia or learning disabilities, an optokinetically based tracking method was devised. This method quantitatively demonstrated significantly reduced fixation, tracking, and perceptual or visual-span scores as well as 'movement illussions' for 70 cerebellarvestibular sysfunctioning persons with learning disabilities vs 70 controls. Such data tended to validate the hypothesis that cerebellar-vestibular-determined fixation and tracking mechanisms predispose dyslexic or learning disabled individuals to visual reading disorders. Moreover, a newly revised method is presented which may prove useful in rapidly screening and diagnosing cerebellar-vestibular-determined reading and learning disordes from those of other origins. Additional independent studies using significantly larger samples and asymtomatic or 'normal' controls are required for further validation and development of the method.