Newswise — Although we know from observation and experience that an individual's response times and decision-making processes slow as they age, research has not been able to pinpoint the reason.
Wythe Whiting, associate professor of psychology at Washington and Lee University, hypothesizes that a breakdown of the brain's neural circuitry may be the answer.
"This 'neural noise' means that we lose neural connections, and we process information at a slower rate," said Whiting, who specializes in the psychology of aging.
Whiting and a team of Washington and Lee undergraduates have been testing his theory in W&L's Cognitive Lab, with interesting results. During the past two years, the researchers have compared the responses of younger adults (18 to 29 years old) with those of older adults (60 and over).
They asked the test subjects to look at a computer monitor and pick out target lines that were different from other lines. For example, they needed to find the green line among the orange lines or the line that tilts left instead of right. The researchers added "noise" in the form of visual static on the computer screen.
"If older adults already have, as I've hypothesized, more neural noise, and you exacerbate it by adding more noise, then the older adults should be much slower in identifying the target lines than the younger adults," Whiting explained. "Basically, the faster they identify the lines, the healthier their nervous system is."
The research team found that the older adults were disproportionately more susceptible to the static noise than the younger adults.
In a previous experiment, Whiting had found that older and younger adults were affected similarly by the external noise—because the subjects knew what they were looking for. "They might get a whole series of trials where the target was always green among orange distracters," he said. "That familiarity meant they could ignore the noise fairly easily."
To get a better sense of what is actually occurring, the team later altered the procedure. "We made the experiment so that subjects didn't know what the target feature was going to be," explained Whiting. "When they didn't really know what to look for, when they simply had to find the odd item, then they were much more susceptible to the noise.
"In the first experiment, they had used their experience and knowledge to filter out the noise. When they didn't have that to rely on, the older adults had more difficulty coping than the younger adults."
Whiting used driving as an example.
"You may know how to drive a car, but the problem is when you have some distracting feature such as the noise of heavy rain. If you're driving in the rain with degrading visual signals, as long as you're traveling along your usual route you're going to do fine. But when you have to travel to a new location in the rain and you're looking for a street sign that you've never seen before, then it's going to be more difficult," he said.
Whiting, who is still in the process of collecting data for his most recent study, noted that the increase in neural noise seems to be a good explanation for some of the slowing we experience as we age. This, along with other physical, sensory declines in vision, hearing, etc., also will affect how quickly we can respond in any given situation, he said
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