“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,” says John Tsotsos, a professor in York’s Department of Computer 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 says. “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 MEG (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 “ST” or “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,” Tsotsos says.

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 on-going experiments with the same team of collaborators.

Tsotsos says 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,” Tsotsos says.

“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 January 12, 2006, in the journal, Proceedings of the National Academy of Sciences of the United States of America.

In addition to Tsotsos, the remainder of the team consisted of researchers in Magdeburg Germany, J.-M. Hopf (Otto-von-Guericke-University and Leibniz Institute for Neurobiology), C. Boehler (Leibniz-Institute for Neurobiology), H.-J. Heinze (University of Magdeburg) and M. Schoenfeld (Otto-von-Guericke-University) and in the United States, S. Luck (University of Iowa).

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For more information, contact:
Melissa Hughes, Media Relations, York University, 416-736-2100 x22097/mehughes@yorku.ca