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Abstract:
Perceptual integration is critical for perception and interpretation of the visual world. Psychophysical studies suggest that these integrative processes for global form and motion develop slowly: when spatial resolution and contrast sensitivity approach adult levels (6-9 months in monkeys), global form and motion perception are still immature. The goal of this study was to investigate the neural development of perceptual integration by using fMRI on anesthetized macaques at different developmental stages. We examined the functional development of higher extrastriate visual areas whose delayed development might be responsible for the late maturation of coherent form and motion perception. We used Glass patterns, random dot patterns in which global structure is defined by the spatial or spatio-temporal orientation of correlated dot pairs to form contour and motion stimuli with identical local statistics but different global forms (e.g. radial, concentric). To compare form and motion processing directly, we used static and dynamic (patterns with both spatial and temporal offset between dots) Glass patterns to activate the ventral and dorsal pathways, respectively. We compared fMRI responses for static and dynamic Glass patterns to those for static and dynamic random noise patterns. Experiments in adult macaques showed stronger activations for static Glass than random patterns in ventral extrastriate visual areas, whereas stronger activations for dynamic Glass than random patterns were observed in dorsal motion areas. Longitudinal study of two infant monkeys from the age of 8 months showed some differential activation for dynamic than random patterns but not for static Glass patterns. These results are consistent with previous perceptual and neurobiological evidence that the dorsal extrastriate pathway develops more quickly than the ventral pathway.
