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Visual attention may involve more than perception

How often do we pick up a pencil, a coffee cup, or a screwdriver without consciously thinking about it—hardly even looking at the item? Ever wonder how that's possible?

Scientists have long suspected that when a tool or some other grabbable object enters our peripheral vision, the brain not only turns its attention to the object but also begins the computations necessary to pick it up. Neuroscientist Todd Handy, Ph.D., together with several other Dartmouth researchers, set out to prove that. What he discovered is that grabbable items can affect visual attention, but that it matters where in the line of vision the item is located.

"There's a fundamental distinction between vision for perception and vision for action," explains Handy, a research assistant professor of physiology and brain science. "What we demonstrated is that things that we can grab—such as tools, cups, things that accord some kind of motor action—are capable of grabbing our attention automatically."

Auspices: Under the auspices of Michael Gazzaniga, Ph.D., director of the Center for Cognitive Neuroscience, Handy's team set up a two-part experiment. Using electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), the team recorded the brain responses of subjects viewing grabbable as well as non-grabbable objects.

The subjects were divided equally by gender and were all right-handed (the effects of gender and handedness will be studied later). One group of subjects peered at a dot, centrally located on a computer screen, while hooked up to an EEG machine. Two objects would appear on either side of the dot—one grabbable, one not. After about a second, horizontal bars would flash over one of the objects. By measuring the electrical activity in the brain, the researchers could determine where the subject's attention was focused. The data indicated that subjects' attention was drawn to the grabbable objects, says Handy, especially when those objects were on the subject's right.

Spatial: Then Scott Grafton, M.D., director of the Dartmouth Brain Imaging Center, and Neha Shroff, a 2002 Dartmouth College graduate who is now a medical student at Vanderbilt, performed fMRI on another group of subjects. These results confirmed that when a subject's spatial attention is drawn to a grabbable object, areas of the brain associated with visually guided actions are activated.

So the investigators concluded that the brain not only recognizes a pencil, a cup, or a screwdriver, but that our attention is drawn to the item and our brain plans how to pick it up. "One of the reasons why we might see grabbable objects drawing our attention to their locations is that to grab things is very complicated," Handy explains. "There's a series of computations the brain has to make. When you look at something, you have to identify where it is, how big it is, and you have to take that visual information and transform it into the appropriate motor commands to actually reach out and grab it." The team's results were published in the April 2003 issue of Nature Neuroscience.

What's remarkable, Handy adds, is that the brain performs these complex acts with hardly any conscious thought. "Spatial attention doesn't just help us identify what something is, like 'I'm looking at a pen,'" he explains. "It actually helps the motor systems compute the programs necessary for grabbing that object . . . attention not just for perception, but attention for action." This understanding is one more step toward figuring out just how the brain works.

Attention: Further research may help to address attention and obsessive-compulsive disorders. And, of course, advertising executives can be counted on to use this new knowledge about grabbing attention to . . . well, grab our attention.

Joyce Wagner

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