Reorganization of global form and motion processing during human visual development.
Wattam-Bell J., Birtles D., Nyström P., von Hofsten C., Rosander K., Anker S., Atkinson J., Braddick O.
The functional selectivity of human primary visual cortex (V1) for orientation and motion direction is established by around 3 months of age [1-3], but there have been few studies of the development of extrastriate visual areas that integrate outputs from V1 [4-8]. We investigated sensitivity and topographical organization for global form and motion with high-density visual event-related potentials (VERPs) in 4- to 5-month-old infants and adults. Responses were measured to transitions between concentrically organized elements (short arc segments for form, dot trajectories for motion) and random arrangements. Adults showed topographically separate responses, with midline motion and more lateral form responses. Of 26 infants, 25 showed significant motion responses but only 13 showed form responses, suggesting more advanced development for extrastriate motion areas than form. Infants' form and motion responses were topographically distinct but contrasted with the corresponding adult topographies, with infants' motion responses more lateral than form responses. These results imply distinct neural sources at both ages and raise the possibility of substantial reorganization of extrastriate networks between infancy and adulthood. We speculate that global motion responses arise from area V5 in infants but are dominated by more medial areas such as V3/V3A and V6 in adults.