Mean IQ scores as a function of age for intervention and control groups in the Perry Preschool and Abecedarian Programs. Perry, circles; Abecedarian, diamonds; intervention group, red symbols; matched control group, blue symbols. Bars indicate SEs. Data from High/Scope and from the Carolina Abecedarian Project and the Carolina Approach to Responsive Education, 1972–1992.

Academic, economic, and social outcomes for the Perry Preschool and Abecedarian Programs. (A) Data from the Perry Program collected when the individuals were 27 years old (High/Scope). >10th percentile achievement, children who scored above the lowest 10% on the California Achievement Test (1970) at age 14; HS Grad, number of children who graduated high school on time. (B) Data from the Abecedarian Program collected when the individuals were 21 years old (Carolina Abecedarian Project and the Carolina Approach to Responsive Education, 1972–1992). Red bars, intervention group; blue bars, control group.

Rates of return to investment in human capital as function of age when the investment was initiated. The data were derived from a life cycle model of dynamic human capital accumulation with multiple periods and credit constraints. Investments were initially set to be equal across all ages. r represents the cost of the funds. Data are from Cunha et al. (19).

Sensitive period for remediation of aberrations in macaque social behavior caused by early life affiliative bond disruption. Young monkeys whose mothers were present in the social group for the first 6 months of life (filled blue circles; n = 6) spent very little time engaged in self-comforting behaviors (thumb sucking and rocking) during the first year of life. In contrast, young monkeys who experienced removal of their mother from their social group at 1 week of age (open red circles; n = 6) spent significantly more time displaying self-comforting behaviors throughout the first year of life (ANOVA; P < 0.05). Introduction of a surrogate, nurturing mother at 1 month of age (red triangles; n = 3) was effective in preventing the development of self-comforting behaviors. In contrast, introduction of a surrogate mother at 1.5 months of age was less effective in ameliorating self-comforting behaviors (filled squares; n = 3), and introduction of a surrogate mother at 2–2.5 months of age (filled diamonds; n = 3) was ineffective in ameliorating self-comforting behaviors. Bars indicate SEs. Data are from McCormick et al. ().

Sensitive period for second language acquisition. English language proficiency scores as a function of age of arrival in the United States for a group of Chinese and Korean adult immigrants (n = 46). All subjects were students or faculty at the University of Illinois and had been in the United States for at least 10 years before testing. The test measured a variety of grammatic judgments. Data are from Johnson and Newport (43).

Functional and structural brain plasticity in the central auditory system of the barn owl. (A) Functional plasticity. Sensitive period for the visual calibration of the auditory system’s map of interaural time difference (ITD) in the midbrain. The data indicate mean adaptive shifts in the tuning of neurons in the optic tectum to ITD in 6 owls (different symbols) that resulted from experience with chronic displacement of the visual field with prismatic spectacles, beginning at different ages. Data are from Brainard and Knudsen (51). (B) Structural plasticity. Adaptive elaboration of axons and synapses in the brains of juvenile owls in response to experience with prism spectacles. Axon and synapse labeling in the external nucleus (ICX) after a tracer injection into the central nucleus (ICC) in a normal adult (typical) and in an owl that had acquired a learned ITD map as a juvenile (trained). Data are from DeBello et al. (52). (C) Increased adult plasticity. Early training leaves a memory trace that increases the capacity for functional plasticity in the adult brain. The data compare shifts in the ITD map in two typically reared adults (blue open symbols) with shifts in the ITD maps in three adults that had learned the alternative ITD map previously as juveniles (red filled symbols). Data are from Knudsen (53). Recent experiments indicate that the increased functional plasticity in previously trained adults is due to the persistence of altered architecture (see B) acquired during juvenile learning (54).