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2008-06-03 12:05:44
Jeanna Bryner
Senior Writer
LiveScience.com Mon Jun 2, 9:50 AM ET
Humans can see into the future, says a cognitive scientist. It's nothing like
the alleged predictive powers of Nostradamus, but we do get a glimpse of events
one-tenth of a second before they occur.
And the mechanism behind that can also explain why we are tricked by optical
illusions.
Researcher Mark Changizi of Rensselaer Polytechnic Institute in New York says
it starts with a neural lag that most everyone experiences while awake. When
light hits your retina, about one-tenth of a second goes by before the brain
translates the signal into a visual perception of the world.
Scientists already knew about the lag, yet they have debated over exactly how
we compensate, with one school of thought proposing our motor system somehow
modifies our movements to offset the delay.
Changizi now says it's our visual system that has evolved to compensate for
neural delays, generating images of what will occur one-tenth of a second into
the future. That foresight keeps our view of the world in the present. It gives
you enough heads up to catch a fly ball (instead of getting socked in the face)
and maneuver smoothly through a crowd. His research on this topic is detailed
in the May/June issue of the journal Cognitive Science,
Explaining illusions
That same seer ability can explain a range of optical illusions, Changizi
found.
"Illusions occur when our brains attempt to perceive the future, and those
perceptions don't match reality," Changizi said.
Here's how the foresight theory could explain the most common visual illusions
- geometric illusions that involve shapes: Something called the Hering
illusion, for instance, looks like bike spokes around a central point, with
vertical lines on either side of this central, so-called vanishing point. The
illusion tricks us into thinking we are moving forward, and thus, switches on
our future-seeing abilities. Since we aren't actually moving and the figure is
static, we misperceive the straight lines as curved ones.
"Evolution has seen to it that geometric drawings like this elicit in us
premonitions of the near future," Changizi said. "The converging lines toward a
vanishing point (the spokes) are cues that trick our brains into thinking we
are moving forward - as we would in the real world, where the door frame (a
pair of vertical lines) seems to bow out as we move through it - and we try to
perceive what that world will look like in the next instant."
Grand unified theory
In real life, when you are moving forward, it's not just the shape of objects
that changes, he explained. Other variables, such as the angular size (how much
of your visual field the object takes up), speed and contrast between the
object and background, will also change.
For instance, if two objects are about the same distance in front of you, and
you move toward one of the objects, that object will speed up more in the next
moment, appear larger, have lower contrast (because something that is moving
faster gets more blurred), and literally get nearer to you compared with the
other object.
Changizi realized the same future-seeing process could explain several other
types of illusions. In what he refers to as a "grand unified theory," Changizi
organized 50 kinds of illusions into a matrix of 28 categories. The results can
successfully predict how certain variables, such as proximity to the central
point or size, will be perceived.
Changizi says that finding a theory that works for so many different classes of
illusions is "a theorist's dream."
Most other ideas put forth to explain illusions have explained one or just a
few types, he said.
The theory is "a big new player in the debate about the origins of illusions,"
Changizi told LiveScience. "All I'm hoping for is that it becomes a giant
gorilla on the block that can take some punches."