ABSTRACT The degree to which visual development is governed by nature vs. nurture has been a long-standing topic in vision research. Although much has been learned from animal studies in the last 50 years, relatively little is known about the factors influencing visual development in humans. The current proposal investigates whether factors related to visual experience ( nurture ) vs. preprogrammed biological maturation ( nature ), or both, are important in shaping visual development. To this end, we propose visual psychophysical studies with four different subject populations that tease apart these factors. (A) Fullterm Infants and (B) Healthy Preterm Infants. If early visual experience is the dominant force in visual development, preterm infants should show the same developmental trajectories as fullterm infants when plotted in terms of postnatal age (i.e. age since birth). By contrast, if biological maturation is more influential, preterm infants should match fullterm babies when plotted in postconceptional age (i.e., age since conception). (C) Monozygotic vs. Dizygotic Twins. While both twin types share the same environment and parents, they differ in the degree of shared genetic makeup. We apply a biometrical twin model that can identify the proportion of phenotypic variance in visual performance that can be accounted for by shared environment versus genes. (D) Infants and Children with Early Abnormal Visual Input. Comparisons made between this group (cataract, strabismus, and anisometropia) and healthy controls will address the vulnerability of various aspects of visual processing to abnormal visual experience early in development. Three aims address different levels of visual processing: 1) Subcortical Pathway Processing: We ask if the three main retinogeniculate pathways, Magnocellular (M), Parvocellular (P) and Koniocellular (K), are equally or differentially affected by visual experience, by obtaining contrast sensitivities for luminance, red/green and blue/yellow stimuli, thought to be mediated by these pathways, respectively. 2) Subcortical Input to Cortical Motion Processing: We will obtain an estimate of the extent of P vs. M subcortical pathway input to motion processing using a Motion/Detection threshold ratio paradigm that measures the relative effects of chromatic (P pathway) vs. luminance (M pathway) contrast on motion processing. Previous results from our laboratory suggest that the relative P vs. M input to motion decreases with age, and here we will ask whether this re-weighting process is influenced more by visual experience or biological maturation. 3) Cortical Motion Processing: We will assess global motion processing, which is believed to be a higher-level cortical function. Unlike many previous studies, our global motion stimuli will be scaled to detectability for each subject, such that differences observed across ages/subject groups can be more definitively interpreted. The results of these projects, which will reveal what aspects of visual development are more vs. less amenable to effects of visual experience, may have important implications for treating children with congenital eye disorders. 1 NARRATIVE: The degree to which visual development is governed by nature (i.e., pre-programmed biological maturation) vs. nurture (i.e., visual experience) has been a long-standing topic in vision research. The current proposal investigates this question by conducting infant visual psychophysical studies in subject populations that bear relevance: preterm infants, twin infants and infants born with congenital eye disorders. The results of these studies, which we hope will reveal what aspects of visual development are more vs. less amenable to effects of visual experience, may have important implications for treating children with visual disorders. 2