Worsening vision and dulled reflexes might explain why some older folks have trouble behind the wheel. But researchers from the University of Rochester may have uncovered another possibility: the aging brain may be better at perceiving irrelevant background movement instead of the focusing on the motion of smaller objects — like pedestrians, bicyclists and other cars — in the foreground.
Previous research has suggested that older people, as well as people with depression or schizophrenia, tend to be better at noticing moving objects in the background, which can distract them concentrating on relevant information in the visual foreground.
Scientists also know that in a healthy brain, a region called the middle temporal visual area (MT) is responsible for suppressing background motion and helping people focus on necessary smaller-scale movements. So the team of researchers at Rochester, led by Duje Tadin, decided to find out what happens when the MT is inhibited.
They recruited six healthy, young volunteers and used transcranial magnetic stimulation to apply a mild 1 Hz electrical current for 15 minutes to their MTs; the stimulation temporarily dampened the region’s functioning. The volunteers were then tested on their ability to identify motions of smaller and larger objects.
Interruption of MT functioning led to a heightened ability to see the motion of large, background-like objects, but did nothing to change participants’ ability to recognize the motion of smaller, foreground objects. That suggests that an improperly working MT causes a kind of distracting visual overload and could affect tasks like driving in older adults.
The researchers say their findings may also have implications for diagnosing and treating people with depression or schizophrenia, who similarly tend to focus on large-scale background motion.