In the brain, there are two primary visual pathways, one for identifying objects (perception) and one to guide your arms and legs based on what you see (action). To better understand how these two systems may interact, the Dartmouth team studied whether visual perception, specifically peripheral visual attention, influences motor systems in the brain.
"People have studied peripheral vision and how it helps perception, but nobody really talked about it in terms of helping action," says Todd C. Handy, the lead author and a research assistant professor at the Center for Cognitive Neuroscience at Dartmouth. "There are certain things that we all know attract our attention, like flashing lights and loud noises. Yet, think about how often we grab things without directly looking at them. Now here's evidence that, to help us do this, grabbable objects can literally grab our attention. There's a clear association."
The researchers devised a simple test to measure this connection. They asked their subjects to look at a computer screen with two objects: one was something graspable, like a tool, the other was not graspable, like a cloud or a sailboat. After about a second, a set of horizontal bars flashed over one of the pictures. While concentrating in the center of the screen, the subjects were told to indicate whether the bars appeared on the left or right. The researchers determined where attention was focused when the bars flashed by measuring the electrical activity in the brain with an electroencephalogram (EEG).
"When the bars flashed over a graspable object, the EEG response in the visual cortex was more intense," says Handy. "It shows evidence of attention being specifically drawn to those objects. Interestingly, the effect was more profound when the tool was on the right. It suggests that attention is more strongly drawn to grabbable objects when they are on our right."
Handy's team then used fMRI (functional magnetic resonance imaging), a method that precisely identifies areas of brain activity, to confirm their results. They found that when the tool appeared on the right, the brain's classic motor areas responded to it. If the tool was on the left, the motor areas weren't as active. According to Handy, this indicates that when graspable items are on the right, the motor system recognizes that there is something to grab and attention is drawn automatically to that location.
"People had already shown that simply viewing graspable objects activates motor areas in the brain," explains Handy. "What we didn't know was that graspable items can affect visual attention, and that it matters where these things are in visual space."
The team is now trying to understand whether being right-handed or left-handed influences visual attention and motor activity.
Handy's co-authors on the paper include Scott T. Grafton, professor of psychological and brain sciences and the Director of the Dartmouth Brain Imaging Center; Neha M. Shroff, Dartmouth alum from the Class of '02; Sarah Ketay, research assistant; and Michael S. Gazzaniga, Dean of the Faculty of Arts and Sciences at Dartmouth and a professor of psychological and brain sciences.
This study was funded by the National Institutes of Health.