Studies of children treated for cataract indicate that there are different sensitive periods for different aspects of vision. For example, visual deprivation beginning at 6 months of age prevents the development of normal acuity or peripheral light sensitivity, but has no effect on sensitivity to the global direction of motion, which is affected adversely only by visual deprivation beginning near birth. Our results also indicate that the deleterious effects of visual deprivation are sometimes worse if there was not only deprivation, but also uneven competition between the eyes—because the deprivation was monocular and there was little patching of the non-deprived eye. However the adverse effects of uneven competition are not seen at all points during development or for all aspects of vision. Together, the results are consistent with theories that visual input can affect later development by (a) preventing deterioration of existing neural structures; (b) reserving neural networks (via Hebbian competition) for later refinement; (c) allowing a developmental trajectory to start from an optimal state; (d) allowing recovery from earlier deprivation via the recruiting of alternative pathways; and/or (e) allowing the refinement of previously established structures. Our results indicate that there are timing constraints on each of these mechanims that are manifested as variations in sensitive periods. The implications for visual rehabilitation will be discussed.