New study focuses on eye movement
A scientist has uncovered one of the “missing links” in understanding visual signals that determine where and why we move our eyes to focus on details in our environment.
Brian White, a postdoctoral fellow who works with Douglas Munoz in the university’s Centre for Neuroscience Studies, says: “The findings help us understand what kinds of signals in the natural world are used by our saccadic system [which guides rapid eye movements]. It turns out that visual processing for the system that drives our eye movements is far more complex than previously known.”
Until now, the study of eye movements in the laboratory has relied on testing with very simplistic stimuli, for example bright spots of light shown against a black screen. Instead, Dr. White uses a structured background that more closely simulates our visibly complex and “cluttered” natural world.
The research indicates that a saccadic response to targets in natural backgrounds is much faster than in unstructured backgrounds when target visibility is held constant. This contradicts widely accepted models of visual attention that assume attention and eye movements are simply driven by the most visible stimulus.
The study, which appears on-line in the journal Current Biology, was conducted at Justus-Liebig-University in Giessen, Germany. Also on the team, from J-L-U, are: Professor Karl Gegenfurtner, senior author, and doctoral student Martin Stritzke.
“The natural visual world actually has a fairly regular structure that most people don’t realize exists, and it is believed the brain is both developmentally and evolutionarily adapted to this structure,” Dr. White explains. His group simulated that structure with images generated off-line and presented to subjects on a computer screen.
Using eye-tracking technology, they measured the subjects’ eye movements, then compared them with the eye’s responses to much simpler stimuli that are typically used in the lab. The time to react to targets on the structured background was actually shorter than to the simple stimuli.
The study shows that the system driving our eye movements compensates for reduced visibility of objects in complex natural backgrounds, allowing us to quickly direct our attention to subtle signals. This ensures a fast reaction to critical stimuli that may be camouflaged by their surroundings.
“These findings help us to better understand how the saccadic system operates in naturalistic contexts,” says Dr. White. “This work also integrates basic, low-level vision science with science that tends to focus more on pure motor behaviour. These fields are still fairly separate, so it’s exciting to integrate the two.”
Funding for the study came from the Deutsche Forschungsgemeinschaft Forschergruppe 560 “Perception and Action.”
PLEASE NOTE: A PDF copy of the study is available upon request.
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