Since the pioneering work of Wiesel and Hubel in the 1960s and 1970s, we have known that the primary visual cortex shows evidence of postnatal development and is susceptible to effects of visual experience during an early critical period. It was therefore widely assumed that the maturation of striate cortex presented an important limit on the development of visual function ( Wiesel, 1982 ). However, despite substantial investigation over the past 50 years into the anatomical and physiological processes that take place postnatally in the primate visual system, it remains unclear what neural mechanisms limit the development of vision.