The Older Mind May Just Be a Fuller Mind
By BENEDICT CAREY
People of a certain age (and we know who we
are) don’t spend much leisure time reviewing the research into cognitive
performance and aging. The story is grim, for one thing: Memory’s speed
and accuracy begin to slip around age 25 and keep on slipping.
The story is familiar, too, for anyone who is
over 50 and, having finally learned to live fully in the moment,
discovers it’s a senior moment. The finding that the brain slows with
age is one of the strongest in all of psychology.
Lisa Haney
Over the years, some scientists have
questioned this dotage curve. But these challenges have had an
ornery-old-person slant: that the tests were biased toward the young,
for example. Or that older people have learned not to care about clearly
trivial things, like memory tests. Or that an older mind must organize
information differently from one attached to some 22-year-old who
records his every Ultimate Frisbee move on Instagram.
Now comes a new kind of challenge to the
evidence of a cognitive decline, from a decidedly digital quarter: data
mining, based on theories of information processing. In a paper
published in Topics in Cognitive Science, a team of linguistic
researchers from the University of Tübingen in Germany used advanced
learning models to search enormous databases of words and phrases.
Since educated older people generally know
more words than younger people, simply by virtue of having been around
longer, the experiment simulates what an older brain has to do to
retrieve a word. And when the researchers incorporated that difference
into the models, the aging “deficits” largely disappeared.
“What shocked me, to be honest, is that for
the first half of the time we were doing this project, I totally bought
into the idea of age-related cognitive decline in healthy adults,” the
lead author, Michael Ramscar,
said by email. But the simulations, he added, “fit so well to human
data that it slowly forced me to entertain this idea that I didn’t need
to invoke decline at all.”
Can it be? Digital tools have confounded
predigital generations; now here they are, coming to the rescue. Or is
it that younger scientists are simply pretesting excuses they can use in
the future to cover their own golden-years lapses?
In fact, the new study is not likely to
overturn 100 years of research, cognitive scientists say.
Neuroscientists have some reason to believe that neural processing
speed, like many reflexes, slows over the years; anatomical studies
suggest that the brain also undergoes subtle structural changes that
could affect memory.
Still, the new report will very likely add to
a growing skepticism about how steep age-related decline really is. It
goes without saying that many people remain disarmingly razor-witted
well into their 90s; yet doubts about the average extent of the decline
are rooted not in individual differences but in study methodology. Many
studies comparing older and younger people, for instance, did not take
into account the effects of pre-symptomatic Alzheimer’s disease, said Laura Carstensen, a psychologist at Stanford University.
Dr. Carstensen and others have found, too,
that with age people become biased in their memory toward words and
associations that have a positive connotation — the “age-related positivity effect,”
as it’s known. This bias very likely applies when older people perform
so-called paired-associate tests, a common measure that involves
memorizing random word pairs, like ostrich and house.
“Given that most cognitive research asks
participants to engage with neutral (and in emotion studies, negative)
stimuli, the traditional research paradigm may put older people at a
disadvantage,” Dr. Carstensen said by email.
The new data-mining analysis also raises
questions about many of the measures scientists use. Dr. Ramscar and his
colleagues applied leading learning models to an estimated pool of
words and phrases that an educated 70-year-old would have seen, and
another pool suitable for an educated 20-year-old. Their model accounted
for more than 75 percent of the difference in scores between older and
younger adults on items in a paired-associate test, he said.
That is to say, the larger the library you have in your head, the longer it usually takes to find a particular word (or pair).
Scientists who study thinking and memory
often make a broad distinction between “fluid” and “crystallized”
intelligence. The former includes short-term memory, like holding a
phone number in mind, analytical reasoning, and the ability to tune out
distractions, like ambient conversation. The latter is accumulated
knowledge, vocabulary and expertise.
“In essence, what Ramscar’s group is arguing
is that an increase in crystallized intelligence can account for a
decrease in fluid intelligence,” said Zach Hambrick,
a psychologist at Michigan State University. In a variety of
experiments, Dr. Hambrick and Timothy A. Salthouse of the University of
Virginia have shown that crystallized knowledge (as measured by New York
Times crosswords, for example) climbs sharply between ages 20 and 50
and then plateaus, even as the fluid kind (like analytical reasoning) is
dropping steadily — by more than 50 percent between ages 20 and 70 in
some studies. “To know for sure whether the one affects the other,
ideally we’d need to see it in human studies over time,” Dr. Hambrick
said.
Dr. Ramscar’s report was a simulation and
included no tested subjects, though he said he does have several memory
studies with normal subjects on the way.
For the time being, this new digital-era
challenge to “cognitive decline” can serve as a ready-made explanation
for blank moments, whether senior or otherwise.
It’s not that you’re slow. It’s that you know so much.
