The figure is famous: a deceptively simple line drawing that at firstglance resembles a vase and, at the next, a pair of human faces inprofile. When you look at this figure, your brain must rapidly decidewhat the various lines denote. Are they the outlines of the vase or theborders of two faces? How does your brain decide?
It does so in a fraction of a second via special nerve circuits inthe brain's visual center that automatically organize information intoa "whole" even as an individual's gaze and attention are focused ononly one part, according to Johns Hopkins researchers writing in arecent issue of the journal Neuron.
"Our paper answers the century-old question of the basis ofsubconscious processes in visual perception, specifically, thephenomenon of figure-ground organization," said Rudiger von der Heydt,a professor in the Zanvyl Krieger Mind-Brain Institute. "Early in the20th century, the Gestalt psychologists postulated the existence ofmechanisms that process visual information automatically andindependently of what we know, think or expect. Since then, there hasalways been the question as to whether these mechanisms actually exist.They do. Our work suggests that the system continuously organizes thewhole scene, even though we usually are attending only to a small partof it."
The report, based on recordings of nerve cells in the visualcortex of macaque monkeys, suggests that this automatic processing ofimages is repeated each time an individual looks at something new,usually three to four times per second. What's more, the brain provideswhat von der Heydt calls "a sophisticated program" to select andprocess the information that is relevant at any given moment.
"The result of this organization is an internal datastructure, quite similar to a database, that allows the attentionmechanism to work efficiently," von der Heydt said. "An image can becompared with a bag of thousands of little Lego blocks in chaoticorder. To pay attention to an object in space, the visual system firsthas to arrange this bag of blocks into useful 'chunks' and providethreads by which one or the other chunk can be pulled out for furtherprocessing."
He noted that the research provides the theoretical foundationthat might one day lead to better diagnosis and treatment of humanbrain disorders.
"The last decades have seen rapid progress in the neurosciencesat a very broad front, particularly at the molecular and cellularlevels, and this progress makes it increasingly clear that we stilllack sufficient understanding of brain function at the 'system level,'"he said. "We need to understand the basis of mental processes. Singlecell recording in animals is only one approach to this formidable task.It is complemented by new brain imaging techniques, traditionalpsychophysics, psychology and computational and theoreticalneuroscience. � Understanding the function of the visual cortex willhelp to interpret neurological symptoms in diseases that producedisorders of vision."
This work was funded by grants from the National Institutes of Health.
The paper, "Figure and Ground in Visual Cortex: V2 CombinesStereoscopic Cues with Gestalt Rules" appeared in the July 7, 2005,issue of Neuron (Volume 47).
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