Functional MRI of global and local processing in children

Functional magnetic resonance imaging was used to examine developmental change in hemispheric biases for globally and locally directed analysis of hierarchical forms. In a previous reaction time (RT) study, which presented hierarchical stimuli to the visual hemifields, children 7 to 14 years of age demonstrated an emerging pattern of hemispheric differences. Initially children analyzed local elements more slowly, without a strongly lateralized advantage for local or global level processing. With age, children's development was marked by a left hemisphere advantage for local level processing that resembled an adult's and a trend toward a right hemisphere advantage for global. In the current study, 20 children 12 to 14 years old were imaged during attend-global and attend-local conditions to determine whether the developmental change in cognitive measures corresponded to a change in distribution of functional activation. Children formed two groups based on their RT performance, immature-bilateral (IB) or mature-lateralized (ML). The volume of task-related activation within lateral temporo-occipital regions of interest was compared for global and local conditions between the two groups. The IB children showed greater activation overall for local level processing, comparable activation across the two hemispheres for the global condition, and a trend of right greater than left hemisphere activation for local. In contrast, the ML children displayed right greater than left hemisphere activation during global analysis and the opposite during local processing. Importantly these patterns of functional activation mirror the profiles of RT performance. Together they demonstrate a shift from undifferentiated, bilateral processing toward hemispheric lateralization.