If you find it hard to concentrate on the barrage of images in television ads and hyperactive Web sites, you aren't alone. According to a paper in the latest Science , the brain responds more weakly to multiple images when they're presented together than if they are viewed one after another. But tired Web surfers may have room for hope: The research also suggests that focusing attention can improve the brain's ability to analyze visual clutter.
To investigate whether visual signals interfere with each other in the brain, Sabine Kastner and her colleagues at the National Institute of Mental Health in Bethesda, Maryland, tested volunteers with functional magnetic resonance imaging (MRI). The researchers asked the subjects to focus their attention on the center of a computer screen, then flashed four small images on other parts of the screen--either simultaneously or one after another. As expected, neuron firing in the brain region leading away from the visual cortex was much stronger when the subjects viewed individual images. "This may be a mechanism by which the brain can filter out unwanted information in a cluttered scene," Kastner says.
Next the subjects were told to look in the middle of the screen, but also divert some attention to a specific corner. This spurred a stronger brain response to multiple images than in the first test. The improvement was greatest when the four images were presented together--suggesting, the researchers say, that the effort to pay attention counteracted the distraction from competing images.
These experiments are "elegant and important," says Nancy Kanwisher of the Massachusetts Institute of Technology. But she says more work is necessary to discern whether a visual collage actually suppresses the brain signal to the visual cortex or simply saturates the system. Further study, she says, might employ MRI analysis to separate the brain's responses to each image, and to see whether paying attention improves response to an individual image.