Now, keep up to date
with daily feeds of newly posted stories
about America's Seniors...click on the box
to the left
New study reconciles conflicting data on
mental aging
WASHINGTON, September 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.
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. 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. This study
was supported by the National Institute on
Aging.
Article: "Influence of Age on Practice Effects
in Longitudinal Neurocognitive Change,"
Timothy A. Salthouse, PhD, University of
Virginia; Neuropsychology,
Vol. 24, No. 5.
