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Form and motion coherence thresholds can provide comparable measures of global visual processing in the ventral and dorsal streams respectively. Normal development of thresholds was tested in 360 normally developing children aged 4–11 and in normal adults. The two tasks showed similar developmental trends, with some greater variability and a slight delay in motion coherence compared to form coherence performance, in reaching adult levels. To examine the proposal of dorsal stream vulnerability related to specific developmental disorders, we compared 24 children with hemiplegic cerebral palsy with the normally developing group. Hemiplegic children performed significantly worse than controls on the motion coherence task for their age, but not on the form coherence task; however, within this group no specific brain area was significantly associated with poor motion compared to form coherence performance. These results suggest that extrastriate mechanisms mediating these thresholds normally develop in parallel, but that the dorsal stream has a greater, general vulnerability to early neurological impairment.