|
Challenging a Prominent
Hypothesis
By Dorothy Wright
There is no getting around
it: as we get older, we become slower. According
to a prominent hypothesis, the general slowing
hypothesis, cognitive slowing is the result of
slowing in the speed of a general mechanism that
contributes to many cognitive processes. Yet what
if several different mechanisms are at work, what
if the impact of cognitive aging differs depending
on the task, and what step of the complex reaction
process is affected? These are the kinds of questions
studied by Assistant Professor of Psychology Anjali
Thapar, and her research is yielding results that
run counter to the general slowing hypothesis.
Thapar earned her bachelor’s
and doctoral degrees at Case Western Reserve University.
She joined the faculty of Bryn Mawr College in
1998, after three years as assistant professor
of psychology at Williams College and a year as
a visiting scholar at Northwestern University.
The author of more than
10 publications and 20 presentations at professional
society meetings worldwide, Thapar’s research
focuses on quantitatively modeling the effects
of aging on information processing systems, human
memory and gender differences in cognitive abilities.
She and colleague Roger Ratcliff (Northwestern
University) recently were awarded a $1.4 million
grant from the National Institute on Aging (NIA)
to study the effects of aging on reaction time.
"Over the past 15
years, research has demonstrated that there is
a slowing in our mental capabilities, laying the
groundwork for our knowledge of cognitive aging,"
Thapar explains. "Now we need to understand
the stages, or steps, of a cognitive reaction
that are impacted by aging and to understand whether
all or only specific stages are impacted."
Complex Reaction
Earlier research on cognitive
aging measured reaction time only, Thapar explains.
However, every cognitive reaction involves a complex
series of stages. "Over the last three years,
our data have shown that the cognitive-aging effect
is complex — not only are certain stages
impacted by aging, but cognitive aging also seems
to be task dependent."
Thapar and Ratcliff are
using a quantitative model to study reaction time
for various tasks and to isolate the stages in
which older adults respond more slowly than young
people. "Roger has developed a diffusion
model of reaction time that integrates reaction
time and accuracy," Thapar says. "The
beauty of the model is that it can be applied
to virtually any cognitive domain, such as attention,
memory or language processing. It breaks reaction
time into stages, which allows us to identify
the specific locus of the slowing — not just
to say that older adults are slower."
Mind-Boggling Results
Thapar and Ratcliff’s
recent NIA-sponsored research has yielded surprising
results. One experiment required subjects to discriminate
between two squares of different brightness presented
on a computer screen; in another, subjects were
asked to discriminate between an r and
an s.
"Those two tasks seem
very similar," Thapar says. "What we
found is that older adults are significantly slower
to respond and significantly less accurate than
young adults in the letter discrimination task.
However, in the brightness discrimination task,
older adults are slower and less accurate than
younger adults in the first session; by the second
session — and this is mind-boggling —
older adults respond at the same pace and with
the same accuracy as young adults."
What this shows, Thapar
maintains, is that cognitive aging is task dependent;
and, more specifically, it is stimulus dependent.
"The results of these two experiments are
powerful when taken together," she says.
"They throw the gauntlet down: one cannot
talk about cognitive aging in terms of a general
slowing hypothesis. That is why we need to reexamine
these issues."
Students’ Impact on
Research
Thapar involves undergraduate
students in her research as paid research assistants,
as volunteer research assistants , or to conduct
independent research for their senior theses.
Current projects include research on the effects
of aging on cognition, false memories, gender
differences in cognitive abilities, and the development
of episodic memory in young children.
"The extent to which
my colleagues and I have been successful in engaging
undergraduates in our research really speaks to
the quality of Bryn Mawr’s students,"
Thapar says. "We have a body of students
who are eager to learn. Some of my students are
engaged in doing research because they are interested
in going on to graduate school, but at least half
of my students who have done senior research projects
or worked in my lab had no intention of going
to graduate school for psychology. They are intellectually
curious and want to learn."
Thapar says her students’
work has sparked new research interests. "My
current research into gender differences stems
directly from a former student’s interest
in the area," she explains. "She had
done some research as a group project in her junior
year, which had some surprising results. She pursued
this area through the summer research program
and her senior thesis. Now this is one of my own
active research areas. This demonstrates the bi-directionality
of the flow of knowledge between faculty and students
at Bryn Mawr."
The involvement of graduate
students has enriched the research environment.
"We have a wonderful, collaborative research
group," Thapar says. "Undergraduates
see what it is like to work with someone who is
a little more advanced. They have a sense of community.
And graduate students provide quite a lot of mentoring,
which allows me to do all the work that I need
to do."
Workshop Method
Thapar teaches courses, labs
and seminars on cognitive psychology, cognitive
neuroscience, experimental methods and statistics,
and human memory, among others, often using what
she describes as a workshop method.
"My approach to teaching
is to use a hook — to start out with an example
that we are all interested in and can relate to
— and go from that superficial level to the
scientific level," she explains. "I
want my students to consider what we know about
an area, what questions are still remaining, and
how we would go about doing research in this area."
Thapar’s personal
experiences as a child taught her the value of
critical thinking. Born in India, she spoke Hindi
and Punjabi until she moved to the United States
at the age of six, when school psychologists discouraged
her parents from allowing her to speak her native
languages. "In the mid-‘70s, psychologists
believed bilingual children were at a disadvantage
in acquiring new skills, a conclusion that was
based on research that we now know was methodologically
unsound," she explains. "Later research
showed that, in fact, bilingual children are better
than monolingual children at acquiring new skills.
We’ve done a 180-degree turn. That taught
me a good lesson, and it is something I stress
with my students: when you review the results
of a study, be critical.
"Science works best
when we are critical," Thapar concludes,
"because a stronger theory emerges from the
midst of criticism."
About the Author
Dorothy Wright contributes
news and feature articles on science, technology,
engineering and general interest topics to a variety
of publications, including Civil Engineering,
Engineering News Record and Bryn Mawr
Now.
|
