Light sensitivity in peripheral retinal fields of dyslexic and proficient readers

A biochemical analysis of people with chronic fatigue who have Irlen Syndrome: speculation concerning immune system dysfunction

This study investigated the biological basis of visual processing disabilities in adults with Chronic Fatigue Syndrome. The study involved 61 adults with symptoms of Chronic Fatigue Syndrome who were screened for visual processing problems (Irlen Syndrome) and divided into two groups according to the severity of symptoms of Irlen Syndrome. Significant variations were identified in blood lipids and urine amino and organic acids of the two groups, which may be indicative of activation of the immune system due to some infective agent. It was suggested that metabolic profiling may help the development of more valid diagnostic categories and allow more investigation of immune system dysfunction as a possible causal factor in a range of learning and behaviour disorders.

The familial incidence of symptoms of scotopic sensitivity/Irlen syndrome: comparison of referred and mass-screened groups

The familial incidence of Scotopic Sensitivity/Irlen Syndrome was investigated in two samples. One sample involved parents and siblings of 126 children identified with symptoms who had been referred for screening. The other sample involved parents and siblings of 33 children who had been identified with symptoms through mass screening of all children in Grades 3 to 6 at two local schools. Two different samples were taken to investigate the possibility of parental referral bias. Familial incidence may be inflated in a referred sample because some parents may be aware of their own symptoms and actively seek assistance. For the sample of children referred for screening, there was an 81% chance of either one or both parents showing similar symptoms and a 76% chance of siblings being similarly affected. For the sample of children identified through school screening, there was an 85%, chance of either one or both parents showing similar symptoms and a 54% chance of siblings being similarly affected. The data confirm previous estimates of incidence and suggest that Scotopic Sensitivity/Irlen Syndrome may be a genetically-based deficit in visual processing.

Scotopic sensitivity/Irlen syndrome and the use of coloured filters: a long-term placebo controlled and masked study of reading achievement and perception of ability

This study investigated the effects of using coloured filters on reading speed, accuracy, and comprehension as well as on perception of academic ability. A double-masked, placebo-controlled crossover design was used, with subjects being assessed over a period of 20 mo. There were three treatment groups (Placebo filters, Blue filters, and Optimal filters) involving 113 subjects with "reading difficulties", ranging in age from 9.2 yr. to 13.1 yr. and with an average discrepancy between chronological age and reading age of 1.8 yr. The 35 controls (who did not use coloured filters) ranged in age from 9.4 yr. to 12.9 yr., with an average discrepancy between chronological age and reading age of 2.1 yr. The treatment groups increased at a significantly greater rate than the control group in reading accuracy and reading comprehension but not for speed of reading. For self-reported perception of academic ability, two of the three treatment groups showed significantly greater increases than the control group. The larger improvements for treatment groups in reading comprehension may be related to a reduction in print and background distortions allowing attention to be directed to the processing of continuous text rather than to the identification of individual words. A reduction in print distortion, however, may not be sufficient to generate improved word-identification skills without additional remedial support, and this may be indicated by the nonsignificant increase in rate of reading.

Contrast sensitivity differences between proficient and disabled readers using colored lenses

Colored overlays or lenses (e.g., Irlen lenses) have been used in attempts to remediate reading difficulties. The present study included four middle-socioeconomic status (SES) adults and four middle-SES children with reading disabilities as well as an equal number of nondisabled readers of the same age groups and SES. Examined were (a) the relationship of wavelength (lens color) to visual grating performance, (b) the effect of reading disability on performance with each lens-color/luminosity-grating combination, (c) group performances on a visual detection task with the clear and chromatic lenses, and (d) peripheral retinal brightness thresholds. The spatial frequency of the gratings (and not the lens color) permitted subjects with reading disabilities to be differentiated from the proficient readers. Subjects with reading disabilities displayed significantly lower contrast sensitivity when tested with sine-wave gratings, as well as displaying higher brightness thresholds in the peripheral retina.

Dark adaptation in disabled readers screened for Scotopic Sensitivity Syndrome

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.

Visual perceptual differences in the dyslexic reader: evidence of greater visual peripheral sensitivity to color and letter stimuli

The present study replicated the 1987 work of Geiger and Lettvin and of Grosser and Spafford in 1989 in providing evidence for greater peripheral sensitivity to individual letter and color stimuli for 10 dyslexics as compared to 10 normal readers. Earlier studies have demonstrated that dyslexics tend to favor clearer images in the peripheral retina as compared to the foveal advantage of proficient readers. For letter and color stimuli individually presented there was a statistically significant difference between dyslexics and proficient readers based on the ability of dyslexics to recognize both letter and color stimuli at greater peripheral distances from the point of fixation. This study directly supports the consideration of visual perceptual factors in the identification and discussion of dyslexia.

The social misperception syndrome in children with learning disabilities: social causes versus neurological variables

Family shortcomings or other intrinsic psychological deficits are frequently viewed as contributing factors to the social misperceptiveness frequently seen in children with learning disabilities. This article attempts to synthesize research defining the social problems of some children with learning disabilities. Particularly emphasized is the role of communication skills deficits. Breakthroughs in neurophysiology negate, to a large extent, traditional emphases on family dysfunction, school failure, or personality distrubances as primary causes of the social problems of some children with LD. Advances in vision and language research allow departure from the social paradigm of the "misperceptive syndrome" to consider constitutionally based hypotheses of neural dysfunction. Neural aberrations are viewed as triggering deficient language processing, which in turn may lead to unsatisfactory social interactions. Several correlates and characteristics of family, school, and environmental systems are discussed in the context of their impact on personality development and on changes in the life adjustments of both children and adults with learning disabilities.

Reply to Stuart and Lovegrove's question, "visual processing deficits in dyslexia: receptors or neural mechanisms?"

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.

Visual processing deficits in dyslexia: receptors or neural mechanisms?

In 1989 and 1990 Grosser and Spafford attributed abnormalities in the peripheral vision of dyslexic subjects to an anomalous distribution of rods and cones. We argue that at the light levels used in these experiments cone responses should dominate both central and peripheral vision. A more likely explanation of their findings is that there is a postreceptoral deficit in the transient visual channel. This hypothesis is supported by independent anatomical, physiological, and psychophysical evidence.