Critical period

A critical period is a developmental window when experience has unusually strong effects on a capacity or system. Its effects may become difficult or impossible to reverse after the window closes.

Sensitive period: A developmental window when experience has especially strong effects, though later learning remains possible. It distinguishes heightened responsiveness from the stricter limits often associated with critical periods.
Visual development: The maturation of visual abilities and neural circuits from infancy onward. Early visual experience can shape these circuits during a well-studied critical period.
Konrad Lorenz: An Austrian zoologist who studied animal behavior and helped establish ethology as a field. His observations of imprinting helped establish early evidence for time-limited learning.
Adult neurogenesis: The formation of new neurons in the adult brain. It shows that some forms of neural change continue beyond early developmental windows.
Neural plasticity: The nervous system’s capacity to change its structure or function in response to experience. Critical periods are phases of unusually high experience-dependent neural change.
Imprinting: A form of rapid learning in young animals that produces lasting social or behavioral preferences. Its timing in young birds became an influential example of learning during a critical period.
Hubel and Wiesel: Neuroscientists David Hubel and Torsten Wiesel, known for studies of visual processing in cats and monkeys. Their experiments on visual deprivation revealed a limited window for normal visual-circuit development.
Critical period for language acquisition: The proposed early-life window when first-language learning proceeds especially readily. This specific claim is debated, unlike the broader evidence for critical periods in sensory systems.
Synaptic pruning: The elimination of synapses as nervous systems develop and refine their connections. Pruning helps reshape circuits during developmental windows of heightened plasticity.
Language acquisition: The process by which humans learn to understand and produce language. The timing of first-language exposure is central to debates about developmental windows.

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