Plasticity & Critical Periods
Hubel and Wiesel demonstrated that some neurons were only responsive to information that came from a single eye, a phenomenon they referred to as “ocular dominance”. Intriguingly, neurons that are tuned to a particular eye cluster together in anatomical columns in the visual cortex of the brain. They called these “ocular dominance columns”. They also measured how distinct neurons respond to distinct visual features, such as the orientation of a line projected on a screen, or specific patterns of lines. These experiments were instrumental to our understanding of visual processing.
This precise organization called to question the role that experience plays in the development of the visual system. In a series of papers, Hubel and Wiesel showed that blocking visual input from one eye during the first few months of life dramatically altered the organization of the columns. When an eye of an adult cat was deprived of input, the organization of the ocular dominance columns did not change. Hubel and Wiesel concluded that such plasticity is limited to early life, and called this a ‘critical period’ of visual cortex development. The discovery of critical periods demonstrated how experience shapes the developing brain’s circuitry, thus perception of the external world. This finding applies across all sensory systems, and even has been shown to be present in the development of social behavior and language acquisition. This critical period of visual plasticity forms the basis for medical interventions in strabismus and amblyopia in children.