Internet users might be driven to distraction by Web sites cluttered with advertising and extraneous information. However, a York scientist and a team of researchers have uncovered new evidence that the brain cleans up images for us by suppressing certain visual areas.
“In effect, the visual capacity of the brain is similar to a bull’s-eye, or a spotlight, but with a complex dark ring around it,” explained John Tsotsos (right), a professor in York’s Department of Computer Science & Engineering, Faculty of Science & Engineering, and co-author of a study on the topic, published last week. Tsotsos is director of York’s Centre for Vision Research and Canada Research Chair in Computational Vision.
“Suppose you are looking at your computer screen and are paying attention to a word while reading, or any other item of interest. This is the ‘target’ of the bull’s-eye – the area which the brain works to enhance, while filtering out the surrounding ring of data,” Tsotsos said. “It definitely provides an explanation as to why objects near the location of fixation, such as banner or pop-up ads, are not perceived as well as advertisers would like them to be.”
The study, which used magnetoencephalography, a technique that measures changes in magnetic fields in the brain, showed that within fractions of a second, this target becomes surrounded by a suppressive zone in the visual cortex. This proves a theory first put forth by Tsotsos in 1990 called the “selective tuning” model of visual attention. Previous experiments have demonstrated the theory measuring human’s visual behavior; this new set of experiments is the first to show neurophysiological changes in the brain for such images that are consistent with the theory.
Scientists previously believed that the brain worked in a simple hierarchical manner, with the visual cortex giving preferential treatment to the most relevant visual task.
“Really, what we’re looking at is an enhanced response at the focus of attention, suppressed response in a narrow zone surrounding the focus of attention, and a rebound at a more distant location,” said Tsotsos.
However, researchers aren’t yet certain precisely how large this area of suppression is. Tsotsos’ theory predicts that the size of this ring of suppression is related to the size and type of objects attended to in the centre; the more complex and large the object, the larger the ring of suppression. This is the topic of ongoing experiments with the same team of collaborators.
Tsotsos said these findings may aid greatly in the design of display screens, particularly “heads up” displays used by pilots, and, increasingly, in dashboard navigation systems in cars. The results are important in situations where visual information must be very quickly understood.
“It’s critical that we look not only at the design and positioning of these displays, but also how the onscreen information is organized. We’re learning how to make the best use of this limited visual capacity, and what kinds of positioning to avoid in order to optimize our visual resources,” explained Tsotsos.
“It seems everybody tries to cram as much info as possible onto screens, hoping we will be able to absorb everything, but the brain just doesn’t work that way.”
The study, “Direct neurophysiological evidence for spatial suppression surrounding the focus of attention in vision”, was published Jan. 12 in the journal, Proceedings of the National Academy of Sciences of the United States of America.
In addition to Tsotsos, the team consisted of researchers from Otto von Guericke University of Magdeburg, Germany, the Leibniz Institute for Neurobiology in Magdeburg, and the University of Iowa.