The relationship between early visual processing and reading ability : investigation of temporal processing in adults and children

Evidence from psychophysical, physiological and neuroimaging studies suggests that functioning of the magnocellular pathway, which is specialized for processing moving stimuli at low-contrast conditions, correlates with reading performance. Nevertheless, the magnocellular-deficit hypothesis remains somewhat controversial. Some researchers continue to publish conflicting evidence, although differences in subject selection criteria and visual stimuli may contribute to discrepant findings. Recent functional neuroimaging studies provide compelling evidence that, in response to moving stimuli at low-contrast conditions, dyslexics evidence a characteristic pattern of physiological under-activation in V5 (MT), an extrastriate area predominated by magnocellular input. Results from this psychophysical study support the hypothesized relationship between magnocellular function and reading ability for adults, but not for children and adolescents. The psychophysical stimuli used in this study might help to advance neuroimaging of early visual correlates with adults. Conversely, these stimuli offer questionable utility to the development of screening instruments that might one day predict developmental dyslexia with young children.