Colloquium: Critical Periods Re-examined: Lessons from Cataract-Reversal Patients

Children who were born with, or developed, dense, central cataracts afford an opportunity to investigate the effects of visual deprivation in humans. The cataracts are removed surgically and the treated eyes are fitted with contact lenses to focus visual input. When the cataracts were present from birth, many visual abilities fail to develop normally (e.g., acuity; motion perception; recognition of facial identity), a pattern indicating that early visual input is necessary to set up, or preserve, the neural architecture that allows these abilities to be refined later in development. Nevertheless, recent evidence indicates that some visual abilities are spared (e.g., biological motion; face detection) and/or can be rehabilitated long after the critical period (e.g., acuity). Collectively, the results reveal that there are different constraints on plasticity for different visual functions and at different points in development.