Article1993

A Defective Visual Pathway in Children with Reading Disability

Stephen W. Lehmkuhle · Ralph P. Garzia · Tina Hash · John A. Baro

163 citations0/0 files storedNew England Journal of Medicine

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Reading and Literacy Development Visual perception and processing mechanisms Developmental and Educational Neuropsychology

Abstract

BACKGROUND: The possibility that reading disability in children is associated with visual problems is in dispute. We sought to test the existence of this association by using electrophysiologic techniques to measure the processing of visual information in the magnicellular and parvicellular visual pathways of the brain. METHODS: Visual evoked potentials were measured with scalp electrodes in children 8 to 11 years old who were normal readers and in those with reading disability. The potentials were measured for targets with low (0.5 cycle per degree of visual angle) and high (4.5 cycles per degree) spatial frequency, surrounded by either a steady background or a uniform-field flickering 12 times per second. A flickering field normally reduces the amplitude and increases the latency of a transient potential evoked by a low-spatial-frequency target, which preferentially excites the magnicellular visual pathway, but has little effect on the response to a high-spatial-frequency target. RESULTS: With a steady background, the latencies of the early components (N1 and P1) of the visual evoked potentials were longer in the reading-disabled children than in the normal readers when the low-spatial-frequency target was used, but not when the high-spatial-frequency target was used. In normal readers, the flickering background increased the latency and reduced the amplitude of the early components, whereas in the reading-disabled children only the amplitude was affected. No differences were observed in either group with the high-spatial-frequency target. CONCLUSIONS: The pattern of results suggests that the response of the magnicellular visual pathway is slowed in reading-disabled children, who do not, however, have a general slowing of the visual response. The possibility that there is a cause-and-effect relation between these findings and reading disability will require further study.

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References

1991Physiological and anatomical evidence for a magnocellular defect in developmental dyslexia.1990Prevalence of reading disability in boys and girls. Results of the Connecticut Longitudinal Study 1980Specific Reading Disability: Differences in Contrast Sensitivity as a Function of Spatial Frequency 1986A theoretical and experimental case for a visual deficit in specific reading disability 1980Reading disability: Spatial frequency specific deficits in visual information store 1977Has the Perceptual Deficit Hypothesis Led Us Astray?

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1999Spatio-temporal contrast sensitivity, coherent motion, and visible persistence in developmental dyslexia 2007M-stream deficits and reading-related visual processes in developmental dyslexia.2009Learning Disabilities, Dyslexia, and Vision 2004Symbol-string sensitivity and children’s reading 2000Controversy about the visual magnocellular deficit in developmental dyslexics 2001Impaired temporal contrast sensitivity in dyslexics is specific to retain-and-compare paradigms 2003Speed of lower-level auditory and visual processing as a basic factor in dyslexia: Electrophysiological evidence

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