In addition, this Virginia researcher found that in three tests of reasoning, spatial visualization, and speed of thinking the age at which these people scored much lower than their peak scores was at the age of 27 years.
According to the paper When does age-related cognitive decline begin?, cognitive aging—that is, the decline in the ability of the brain to think and process information—begins in “healthy educated adults when they are in their 20s and 30s.”
The paper was published online on February 24, 2009, and is in the April issue (volume 30, issue 4, pages 507-514) of the journal Neurobiology of Aging.
The author states in the abstract of his paper, “Cross-sectional comparisons have consistently revealed that increased age is associated with lower levels of cognitive performance, even in the range from 18 to 60 years of age.”
Salthouse disputes the validity of cross-sectional comparisons when applied to cognitive functioning of the brain in young and middle-aged adults because of the wide variance of ages in when these studies say cognitive decline begins.
He states that, “The results of the current project suggest that a major factor contributing to the discrepancy is the masking of age-related declines in longitudinal comparisons by large positive effects associated with prior test experience.”
The author adds, “Results from three methods of estimating retest effects in this project, together with results from studies comparing non-human animals raised in constant environments and from studies examining neurobiological variables not susceptible to retest effects, converge on a conclusion that some aspects of age-related cognitive decline begin in healthy educated adults when they are in their 20s and 30s.”
Page three concludes with a critique of Dr. Salthouse's conclusions.