Abrupt and ramped flicker-defined form shows evidence for a large magnocellular impairment in dyslexia

► We tested contrast sensitivity for flicker-defined form with phantom contours. ► Children with dyslexia and healthy controls were compared in an abrupt onset condition and ramped contrast onset conditions. ► Stimuli alternating at high temporal frequencies are processed by the visual magnocellular system. ► Children with dyslexia showed large reductions in performance on all tasks, indicating impaired magnocellular processing.