Visual motion perception in children with dyslexia: Normal detection but abnormal integration

Studies of the visual system of dyslexics have provided some evidence to suggest that a magno pathway abnormality may be associated with this disorder. Since the magno pathway and its cortical targets are critical for visual motion perception, we investigated motion sensitivity in a group of dyslexic children. We observed significant deficits on a random dot motion coherence test among ten 10-year old dyslexic children compared to age-matched normal readers. Motion sensitivity losses were still evident when measured 1 year later. In a second experiment, we manipulated the number of frames making up the apparent motion stimuli. We observed that whereas children with dyslexia could perform normally with very brief two-frame apparent motion stimuli, indicating motion detection, their rate of improvement with more frames in the stimulus was significantly worse than controls. Our results data suggest that dyslexic children have poor perceptual integration, rather than poor low-level motion detection.