| Visual processing, though seemingly automatic, is complex. Typical humans process objects and faces routinely. Yet, when a disease or disorder disrupts face and object recognition, the effects are profound. Because of its importance and complexity, visual processing has been the subject of many adult functional imaging studies. However, relatively little is known about the development of the neural organization and underlying cognitive mechanisms of face and object recognition. The current project used functional magnetic resonance imaging (fMRI) to identify maturational changes in the neural substrates of face and object recognition in 5-8 year olds, 9-11 year olds, and adults. A passive face and object viewing task revealed cortical shifts in the face-responsive loci of the ventral processing stream (VPS), an inferior occipito-temporal region known to function in higher visual processing. Older children and adults recruited more anterior regions of the ventral processing stream than younger children. To investigate the potential cognitive basis for these developmental changes, researchers implemented a shape-matching task with parametric variations of shape overlap, structural similarity (SS), in stimulus pairs. VPS regions sensitive to high SS emerged in older children and adults. Younger children recruited no structurally-sensitive regions in the VPS. Two right hemisphere VPS regions were sensitive to maturational changes in SS. A comparison of face-responsive regions from the passive viewing task and the VPS SS regions did not reveal overlap. Though SS drives organization of the VPS, it did not explain the cortical shifts in the neural substrates for face processing. In addition to VPS regions, results indicated additional maturational SS changes in frontal, parietal, and cerebellar regions. Based on these findings, further analyses were conducted to quantify and qualify maturational changes in face and object processing throughout the brain. Results indicated developmental changes in activation extent, signal magnitude, and lateralization of face and object recognition networks. Collectively, this project supports a developmental change in visual processing between 5-8 years and 9-11 years of age. Chapters Four through Six provide an in-depth discussion of the implications of these findings. |
