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How Do We Make Sense Of What We See

From: UFO UpDates - Toronto <ufoupdates.nul>
Date: Thu, 22 Nov 2007 08:52:37 -0500
Archived: Thu, 22 Nov 2007 08:52:37 -0500
Subject: How Do We Make Sense Of What We See




Source: Terra Daily.Com - USA

http://tinyurl.com/ypggbx

Nov 21, 2007


How Do We Make Sense Of What We See

Baltimore MD (SPX)
M.C. Escher's ambiguous drawings transfix us: Are those black
birds flying against a white sky or white birds soaring out of a
black sky? Which side is up on those crazy staircases? Lines in
Escher's drawings can seem to be part of either of two different
shapes. How does our brain decide which of those shapes to
"see?" In a situation where the visual information provided is
ambiguous -- whether we are looking at Escher's art or looking
at, say, a forest -- how do our brains settle on just one
interpretation?

In a study published this month in Nature Neuroscience,
researchers at The Johns Hopkins University demonstrate that
brains do so by way of a mechanism in a region of the visual
cortex called V2.

That mechanism, the researchers say, identifies "figure" and
"background" regions of an image, provides a structure for
paying attention to only one of those two regions at a time and
assigns shapes to the collections of foreground "figure" lines
that we see.

"What we found is that V2 generates a foreground-background map
for each image registered by the eyes," said Rudiger von der
Heydt, a neuroscientist, professor in the university's Zanvyl
Krieger Mind/Brain Institute and lead author on the paper.
"Contours are assigned to the foreground regions, and V2 does
this automatically within a tenth of a second."

The study was based on recordings of the activity of nerve cells
in the V2 region in the brain of macaques, whose visual systems
are much like that of humans. V2 is roughly the size of a
microcassette and is located in the very back of the brain. Von
der Heydt said the foreground-background "map" generated by V2
also provides the structure for conscious perception in humans.

"Because of their complexity, images of natural scenes generally
have many possible interpretations, not just two, like in
Escher's drawings," he said. "In most cases, they contain a
variety of cues that could be used to identify fore- and
background, but oftentimes, these cues contradict each other.
The V2 mechanism combines these cues efficiently and provides us
immediately with a rough sketch of the scene."

Von der Heydt called the mechanism "primitive" but generally
reliable. It can also, he said, be overridden by decision of the
conscious mind.

"Our experiments show that the brain can also command the V2
mechanism to interpret the image in another way," he said. "This
explains why, in Escher's drawings, we can switch deliberately"
to see either the white birds or the dark birds, or to see
either side of the staircase as facing "up."

The mechanism revealed by this study is part of a system that
enables us to search for objects in cluttered scenes, so we can
attend to the object of our choice and even reach out and grasp
it.

"We can do all of this without effort, thanks to a neural
machine that generates visual object representations in the
brain," von der Heydt said. "Better yet, we can access these
representations in the way we need for each specific task.
Unfortunately, how this 'machine' works is still a mystery to
us. But discovering this mechanism that so efficiently links our
attention to figure-ground organization is a step toward
understanding this amazing machine."

Understanding how this brain function works is more than just
interesting: It also could assist researchers in unraveling the
causes of - and perhaps identifying treatment for - visual
disorders such as dyslexia.


[Thanks to 'The Norm' for the lead]


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