Iq changes with age
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IQ Changes with Age: A Comprehensive Overview
Heritability of IQ and Age: The Wilson Effect
The heritability of IQ increases with age, a phenomenon known as the Wilson Effect. Studies involving twins and adoption cases have shown that the heritability of IQ reaches an asymptote of about 0.80 by the age of 18-20 and remains at that level into adulthood. Concurrently, the influence of shared environmental factors decreases to approximately 0.10 by the same age range and continues at that level into adulthood.
Cognitive Decline in the General Population
Longitudinal studies indicate that IQ generally declines with age. Performance IQ tends to decline early and rapidly, while verbal IQ declines later and more slowly. This pattern is observed in the general population but differs in individuals with intellectual disabilities, where verbal ability declines more significantly than performance ability.
Age-Related Performance in Cognitive Tasks
Research examining the effects of aging and IQ on performance in two-choice tasks (numerosity discrimination, recognition memory, and lexical decision) found that while performance declines with age, the quality of evidence obtained from stimuli or memory is more significantly affected by IQ than by age. This suggests that higher IQ individuals maintain better decision-making quality despite age-related declines.
Generational Changes and IQ: The Flynn Effect
The Flynn Effect, which describes generational increases in IQ, does not uniformly apply across all ages and ability levels. A study of 10,000 US adolescents found that while IQs increased by 2.3 points at age 13, they decreased by 1.6 points at age 18. Additionally, those with lower IQs (<70) experienced a decline, whereas those with higher IQs (>130) saw an increase. This variability challenges the generalization of IQ trends across the population.
Brain Structure and IQ Changes
Changes in cortical thickness and surface area are related to intelligence. More intelligent children tend to have a thinner cortex at age 10, which thins faster over time. By age 42, a thicker cortex is associated with higher intelligence. Cortical surface area, which is larger in more intelligent children, expands during adolescence and then decreases at a higher rate once expansion is complete.
Stability of IQ Across the Lifespan
Genetic factors play a significant role in the stability of IQ from childhood to old age. Data from the Scottish Mental Surveys of 1932 and 1947 show that genetic influences on intelligence in childhood also affect it in old age. This suggests that genetic factors are crucial in understanding cognitive stability and changes throughout life .
Brain Aging and Cognitive Decline
A longitudinal study of older adults found that while there is significant neuroanatomical decline (e.g., decreases in grey matter and white matter volumes), these changes are not necessarily linked to cognitive deterioration. Verbal and non-verbal IQ measures remained stable over four years, indicating that brain volume reductions do not directly correlate with cognitive decline.
Cognitive Reserve Hypothesis
The cognitive reserve hypothesis posits that individuals with higher IQ can better tolerate age-related brain pathologies, delaying the onset of terminal cognitive decline. However, once decline begins, it progresses more steeply in those with higher IQ. This hypothesis is supported by findings that higher IQ is associated with a delayed onset of decline in perceptual and motor speed, and verbal ability, but not necessarily in spatial ability.
Conclusion
The relationship between IQ and age is complex and influenced by various factors, including genetics, brain structure changes, and cognitive reserve. While IQ tends to decline with age, the rate and nature of this decline can vary significantly based on individual differences and generational changes. Understanding these dynamics is crucial for developing strategies to maintain cognitive health throughout the lifespan.
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