Perceptual evidence for an anomalous distribution of rods and cones in the retinas of dyslexics: a new hypothesis

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.

Central auditory processing disorder in school-aged children: a critical review

The rationale to evaluate for central auditory processing disorder (CAPD) in school-aged children is based on the assumption that an auditory-specific perceptual deficit underlies many learning problems including specific reading and language disabilities. A fundamental issue in this area is whether convincing empirical evidence exists to validate this proposition. Herein, we consider the issue of modality specificity by examining the extent to which reading, language, and attention disorders in school-aged children involve perceptual dysfunctions limited to a single sensory modality. Difficulty in validating CAPD as a diagnostic label is due in large part to use of the unimodal inclusive framework, which has biased the diagnosis to favor sensitivity of test results over documenting the specificity of the deficit. Indeed, empirical research documenting modality-specific auditory-perceptual dysfunction in this population is scarce. Therefore, the existing literature on this topic has not clarified the "true" nature of the problem, and has left many questions about this disorder unanswered. It is argued that demonstrating modality specificity is one way to rule out supramodal disorders as explanations for observed dysfunction. Multimodal perceptual testing is one logical approach to help clarify this area of investigation.

Digit span and other WISC-R scores in the diagnosis of dyslexia in children

The examination of subtest scores on the Wechsler Intelligence Scale is needed to provide confirmatory evidence for various subtest categorizations as there is no consensus about what patterns might be diagnostically useful. The present study supports the use of the ACID/AVID profiles (Arithmetic, Coding or Vocabulary, Information, and Digit Span) as elements in the diagnosis of dyslexia. WISC-R scores from 44 subjects were analyzed for specific subtest patterns of scores which might separate dyslexic individuals from the WISC-R standardization group. Perhaps some WISC-R ACID/AVID profile pattern analyses may be valid in the diagnosis of a stringently defined population of learning disabled individuals such as dyslexic children.

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.

Task-determined strategies of visual process

Lateral masking in the peripheral field of vision obscures letter recognition and is not accounted for by diminished acuity. In measuring lateral masking between letters in the peripheral visual field we accidentally discovered that ordinary readers and severe dyslexics differ markedly in tachistoscopic letter recognition tasks. Tests were devised to measure the differences accurately. Ordinary readers recognize letters best in and near the center of gaze. Recognition falls off rapidly with angular distance in the peripheral field. Severe dyslexics recognize letters farther in the periphery in the direction of reading (English-natives to the right, Hebrew-natives to the left). They have marked lateral masking in and near the center of the field when letters are presented in aggregates. With dyslexia as an example, we proposed that the distribution of lateral masking is a task-dependent strategy in visual perception. To test this notion we designed an active practise regimen for 4 severe adult dyslexics, who within a few months improved sharply in reading. At the same time their test results changed to those of ordinary readers. We conclude that there are switchable task-determined pre-cognitive strategies of vision that can be learned and that the distribution of lateral masking may be part of what is learned.

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.

Light sensitivity in peripheral retinal fields of dyslexic and proficient readers

This present study furthers research on perceptual differences between dyslexics and normal readers which is contrary to the current linguistic approaches to this problem. Specifically, thresholds of light intensity for small retinal areas were examined. As hypothesized, the peripheral retinas of proficient readers evidenced lower thresholds than the peripheral retinas of dyslexic readers. These results are consistent with Grosser and Spafford's previous research which showed that dyslexics were better able to detect colors with their peripheral retinas than proficient readers. This research lends support to the premise that dyslexics' retinas have unusually high cone density in the periphery. Additional research is warranted to improve both diagnosis and treatment of dyslexia.

Wechsler Digit Span subtest: diagnostic usefulness with dyslexic children

The current study supports Levinson's contention (1988) that the diagnosis of dyslexia cannot be based solely on neurophysiological evidence but must be made in conjunction with reading and educational test scores. Contrary to much current research, in the present study specific WISC-R profiles are identified within a stringently defined subgroup of 57 9- to 12-yr-old dyslexic children. Well-defined subtest scatter can differentiate dyslexics from proficient readers. In particular, the Digit Span subtest, which is not routinely administered by psychologists or included in computing Verbal IQ, can be considered an important component of a diagnostic battery. Unexpectedly, Coding emerged with Digit Span as a third factor in a principal component analysis; statistically significant sex differences appeared on the Coding task. Findings appear to confirm the phonological encoding deficiencies displayed by dyslexics on the Digit Span subtest. This study strongly supports consideration of WISC-R subtest differences, along with correlated factors, neurophysiological and perceptual evidence, when diagnosing dyslexic children. Cross-validation is planned.

Are rods and cones of dyslexics anomalous?

Grosser and Spafford (in this journal, 1989) have advanced an hypothesis and presented measurements which they believe support the idea of an excess of cones in the peripheral retinae of dyslexics. This note points out that their hypothesis is based on the erroneous assumption that normals have no peripheral cones. Further, their data can be explained by at least two alternative, though uninteresting, methodological hypotheses, that uncontrolled eye movements or experimenter suggestion (or both) could have produced their results. Finally, the requisite methods for assessing color vision, and the cones, were not met in the study.