Vision

Studies strongly indicate there is a critical period during which normal development of the visual system takes place—a period when environmental information is permanently encoded within the brain. Although the exact time frame of the critical period is not clear, it is believed that by age six or seven years, visual maturation is complete. Animal studies show that if one eye is completely covered during the entire critical period, neurons in the visual pathway and brain connected to the covered eye do not develop normally. When that eye is finally uncovered, only neurons relating to the eye that was not covered function in the visual process. This is an example of "ocular dominance," when cells activated by one eye dominate over the cells of the other.