The complexities and capabilities of the adult visual system are quite remarkable. Perhaps equally impressive is the process by which these abilities are developed and refined during the first few years of life. The experiments described in this proposal are an extension of previous research on one critical aspect of this development, the development of cortical processing of vision. Specifically, the maturation of orientation tuning will be investigated in human infants using both electrophysiological and psychophysical techniques. Four different visually evoked potential (VEP) experiments and three psychophysical studies using preferential looking (PL) or optokinetic nystagmus (OKN) will be conducted. Masking, adaptation, cross orientational inhibition, and the orientation tuning of binocular interactions will be used to examine the development of orientation selectivity. By comparing the developmental time course of orientation selectivity with that of vernier acuity, it should be possible to determine if the development of vernier acuity (also believed to represent a cortical process) depends on, or is in some way linked to, the development of orientation tuning. The relationship between line detection thresholds and vernier acuity will also be explored in infants. These experiments have relevance not only to our understanding of development, but also may provide evidence regarding the mechanisms underlying vernier acuity. The orientation studies may also provide indirect evidence about the development of higher order cortical processes involved in the analysis of motion. Since normal development is easily altered during periods of rapid change, understanding normal visual development have important implications for understanding various anomalies of vision (e.g., amblyopia and strabismus).