January 2003

The Science of Conserving Culture

The Gateway Hypothesis of Substance Abuse

Combining the Liberal Arts, Medicine and Business

Confronting Famine Abroad and Obesity at Home

Integrating Teaching and Research in Mathematics

Challenging a Prominent Hypothesis

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Bryn Mawr College
A newsletter on research, teaching, management, policy making and leadership in Science and Technology

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.

Anjali Thapar

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.

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