Mental Decline in Aging May Be More Gradual Than
Many Have Thought
But - Now convincing evidence that even vocabulary
knowledge and what's called crystallized intelligence decline at older
ages
Sept.
14, 2010 A new look at tests of mental aging reveals a good news-bad
news situation. The bad news is all mental abilities appear to decline
with age, to varying degrees. The good news is the drops are not as
steep as some research showed, according to a study published by the
American Psychological Association.
"There is now convincing evidence that even
vocabulary knowledge and what's called crystallized intelligence decline
at older ages," said study author Timothy Salthouse, PhD. This study was
supported by the National Institute on Aging.
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There is often a striking discrepancy in the age
trends obtained from cross-sectional and longitudinal comparisons of
certain cognitive abilities, as the former frequently reveal nearly
linear declines starting in the early twenties, whereas significant
longitudinal decline seldom occurs until adults are 60 years of age or
older, according to the author.
Longitudinal test scores look good in part because
repeat test-takers grow familiar with tests or testing strategies, said
the University of Virginia psychologist. Factoring out these "practice
effects" showed a truer picture of actual mental aging, according to
Salthouse.
Still, the declines, although pervasive, are
smaller than thought, according to the report in the July issue of
Neuropsychology. That finding contradicts data gathered by the other
major research approach to aging, cross-sectional studies, which compare
the performance of different age groups at the same time.
With both methods subject to bias, "It remains
important to recognize the limitations of each type of study design when
interpreting results," Salthouse said.
To learn what really happens as people age,
Salthouse tackled how different research methods have led to different
findings. Cross-sectional studies that compared the abilities of younger
and older adults showed big drops in key areas. On the other hand,
longitudinal studies suggested that, until about age 60, abilities are
stable or even improve. Which type of study, if either, was right?
To find out, Salthouse analyzed data on five key
cognitive abilities from the longitudinal Virginia Cognitive Aging
Project. Scores were available for 1,616 adults age 18 to more than 80
on tests of reasoning, spatial visualization, episodic memory,
perceptual speed and vocabulary. The data were collected over an average
test-retest interval of two-and-a-half years.
First, Salthouse sorted participants into age
brackets by decade, each with well more than 100 participants, except
for the 80-89 bracket, with 87 participants.
Second, he estimated the size of practice effects
by comparing scores earned on the second test by the longitudinal
participants with scores on a first test by another group of
participants. He also used statistical methods to adjust for the chance
that weaker performers dropped out between the first and second tests.
Practice effects were evident across the board,
allowing test-takers to score higher the second time around not because
they truly were more able, but because they knew the test an
unavoidable byproduct of repeated testing. Although the numbers varied
by ability and age, practice effects were found to be as large as or
larger than the annual cross-sectional differences.
Numbers in hand, Salthouse removed the
practice-related "bonus points." Stripping them out generated a new set
of cognitive scores that could be expected to reflect more accurately
normal mental aging in healthy adults.
With practice effects taken into account, the age
trends in the longitudinal data became more similar to results from
cross-sectional studies in the places where they had diverged. The
different methods now agreed on the downward direction of change.
However, the increments were smaller. In other
words, the mental abilities of younger adults still rose over time, but
not nearly as much. And the mental abilities of older adults still fell
over time, but not quite as much.
Knowing how practice effects, selective attrition
and actual maturation affect how people change over time will put
psychologists in a better position "to evaluate true age changes, and
how they might relate to late-life pathology and everyday functioning,"
Salthouse said.
Salthouse also found that practice effects played a
bigger role in younger than older adults, possibly because younger
people learn better.
"Longitudinal comparisons in people of different
ages may be even more complicated because the amount of longitudinal
change may be partially determined by the individual's learning ability
at a given age," he noted.
Salthouse is a fellow of the American Psychological
Association and other scientific associations, and a past winner of the
APA's William James Award.
The American Psychological Association, in
Washington, D.C., is the largest scientific and professional
organization representing psychology in the United States and is the
world's largest association of psychologists. APA's membership includes
more than 152,000 researchers, educators, clinicians, consultants and
students. Through its divisions in 54 subfields of psychology and
affiliations with 60 state, territorial and Canadian provincial
associations, APA works to advance psychology as a science, as a
profession and as a means of promoting health, education and human
welfare.
Keep up with the latest news for senior citizens, baby
boomers
Sept.
14, 2010 A new look at tests of mental aging reveals a good news-bad
news situation. The bad news is all mental abilities appear to decline
with age, to varying degrees. The good news is the drops are not as
steep as some research showed, according to a study published by the
American Psychological Association. 
