January 28, 2011

Study Explains Why Grandma Isn’t a Good Driver

(Ivanhoe Newswire) -- When elderly drivers hop behind the wheel, they are often shaken with the reality that they might not be able to easily see other cars, pedestrians or cyclists moving around them. This daunting effect of aging isn't a result of a reduced ability to perceive moving objects but rather a heightened awareness of the backdrop against which these objects move, according to a new study.

A team of scientists led by University of Rochester Professor Duje Tadin has figured out the cause of this phenomenon, and the results could not only help train elderly people to be better drivers, but they could also help psychiatrists better understand abnormal brain processes in psychological conditions like depression and schizophrenia.

In a healthy, young person, the middle temporal visual area (MT) in the brain actively suppresses irrelevant background motion so that the object of interest can be concentrated on. Previous studies have found that elderly people, as well as those with psychological conditions such as schizophrenia and depression, are better at perceiving motion in the background.

"The amount of visual information around us is huge, and we don't have the brain power to process it all," Tadin was quoted as saying. "Evolutionarily speaking, moving objects are the most important visual features to detect quickly because they could be your lunch, or they could want to eat you for lunch. It just makes sense that our vision prioritizes processing them."

Tadin and his colleagues discovered that the MT was responsible for this effect by using a technique called Transcranial Magnetic Stimulation (TMS). By precisely placing magnetic coils on the back of a subject's head, the scientists stimulated the MT with electrical signals for 15 minutes to temporarily inhibit its functioning. Then, while the MT was less active, they tested how well subjects identified motions of smaller and larger objects. They found that when the MT was inhibited, subjects had an easier time identifying the motion of large, background-like objects. These results indicate that an improperly-functioning MT may be the cause behind better-than-normal perception of background motion in older adults.

The researchers say this study provides insight into the diagnosis of schizophrenia and depression, as well as aging.

SOURCE: Journal of Neuroscience, published online January 25, 2011