Processing Speed, More than Memory, Impacts Communication in Normal Aging

Newswise — In a five-year Language Across the Life Span Project funded by the National Institute on Aging, University of Kansas Distinguished Professor Susan Kemper has identified the aging brain’s slower processing speed as the prime candidate in typical communication problems of healthy older adults.

Kemper devised a dual-task procedure that precisely measured and analyzed the ability of young and older adults to do two things at once — keep a cursor on a moving target on a computer screen while responding to questions — to measure how aging affects communication abilities.

The dual-task procedure allowed the researchers to track the moment-by-moment fluctuations in individuals’ tracking performances as a function of what they were saying. While it was not surprising that younger adults did better at dual-tasking, both young and older adults hit a “functional ceiling” when the target was moving rapidly or when the questions required thoughtful and complex responses.

Producing long, complex sentences with lots of nouns and verbs was costly to tracking performance, so young and older adults used short, simple sentences when tracking to avoid hitting that functional ceiling, Kemper said.

But another pattern also emerged: Young adults often limited what they were saying to stay with the rapidly moving target, while older adults sacrificed target tracking to provide complex, thoughtful responses.

The researchers were also interested what determined the "height" of the functional ceiling.

“We didn’t find much evidence that working memory or long-term memory play a role in dual-tasking, but we think that processing speed does,” said Kemper. “What I think is going on is that you have to rapidly switch your attention from tracking to talking, going back and forth pretty rapidly, and that’s where the processing speed really comes in. Older adults seem to be slower at switching between tasks so their functional ceiling is lower.” Further, a close analysis of the responses investigated whether the demands of planning what to say, actually saying it or recovering from what had just been said was costly in terms of tracking performance.

“We could look at tracking performance as reflecting the difficulty of the next sentence individuals were going to say, the one they were actually producing or the one they just said,” Kemper said.

While planning and producing complex sentences cost both younger and older adults tracking precision, planning seemed to be most costly for both older and younger adults. Older adults also needed recovery time after producing a complex sentence.

Kemper said that the study marks a milestone in methodology and in the precise measurement of language and communication problems. She also stressed that language and communication problems, especially those that arise during dual-tasking, may be indicators of the onset of dementias like Alzheimer’s disease. This approach may also be useful for evaluating the efficacy of treatments for neuropathologies, she said.

“We know that there are brain markers even for people in their 40s who may be on the verge of developing dementia,” Kemper said. “But those are revealed by very expensive tests that are not widely available. So perhaps language and communication might provide early warning signs that might be picked up and also serve as an access point for trying to develop interventions.”Results of the study have been most recently reported in Journal of Gerontology: Psychological Sciences, March 2011, volume 66:2, and Psychology and Aging, December 2010, volume 25:4.

Kemper is the Roy A. Roberts Distinguished Professor of Psychology at KU and a senior scientist with the Gerontology Center at the Life Span Institute. Key collaborators include the KU Digital Electronics and Engineering Core specialists from the Center for Biobehavioral Neurosciences in Communication Disorders, supported through a grant from the National Institute on Deafness and Other Communication Disorders.