York study points to a cause of bad driving

Cut off while driving on the 401 lately? Poor driving habits and other accident-causing behaviour may be less about bad manners and more about people’s inability to create a reliable visual map.

That’s what Doug Crawford, Canada Research Chair in Visual-Motor Neuroscience at York’s Centre for Vision Research, found in his study, titled "Transcranial Magnetic Stimulation over Posterior Parietal Cortex Disrupts Transsaccadic Memory of Multiple Objects", a collaborative effort between Crawford and York PhD candidates Steven Prime and Michael Vesia.

Published this month in The Journal of Neuroscience, the study found that people’s ability to identify and remember the placement of objects in the world, particularly when their eyes are moving, is easily disrupted.

Left: Doug Crawford

Researchers have long known that people have the ability to remember the locations of three to four objects in the visual scene when looking around. This helps the brain create a continuous perception of the world. But when York researchers introduced a magnetic pulse to the parietal cortex portion of the brain, study subjects temporarily lost this ability, especially when they shifted their vision to a new location.

"These findings are significant for everyday activities like driving," said Doug Crawford. "On the highway you have to keep checking over your shoulder and in the mirror to remember what is around you so you can react quickly if someone cuts you off or there’s an obstacle ahead."

The posterior parietal cortex (PPC) manipulates mental images and integrates the sensory and motor portions of the brain. The average person has three to five eye movements per second and the PPC prevents these images from being perceived as a jumble, which Crawford likens to a cubist mural, such as Picasso’s Guernica.

"Imagine if that ability broke down, as it does in our experiment, except not from a magnetic pulse, but because of stroke, degenerative neurological disorders, normal aging, fever, alcohol use or fatigue, so that you could only remember one object and not know where it was unless it is right in front of you? This could be creating a lot of the fatal accidents on our highways," Crawford said.

To test the human ability to remember objects and their placement while surveying a scene, the researchers monitored the eye movements of eight subjects using a head-mounted eye-tracking system. Subjects had to remember and compare various images on a display screen while magnetic pulses were safely delivered to the parietal cortex, pinpointed using MRI technology.

The new study shows that those whose visual memory is degraded by fatigue, intoxication, age and other disruptions in the brain may have the illusion of perceiving the full scene when, in reality, their vision is merely shining a spotlight on small areas and not recording the full view in memory.

"I strongly suspect that this capacity is degraded in a lot of people walking around out there and it’s not being tested in venues like driving exams," Crawford said.