The premise that mature visual function depends upon the nature of visual experience during development is based primarily on experiments showing that visual deprivation during a 'critical' period early in life causes abnormalities in visual cortex and an enduring loss of spatial vision (amplyopia). There is, however, little evidence that early visual experience atually enables mature vision. Experments in this thesis provide such evidence. The measurement of optomotor responses daily from eye opening permanently enhances optomotor sensitivity and the perception of visual motion. The plasticity allowing this enhancement is transient and peaks in efficacy before the start of the classical 'critical ' period for ocular dominance plasticity. The enhancement is dependent upon optomotor responses generated by the movement of high spatial frequency visual stimuli, and is mediated by the visual cortex. These studies show that a form of experience-dependent plasticity, distinct from that of the critical period, enables mature motion vision. / viii, 107 leaves : ill. (some col.) ; 28 cm.