by Marte Otten
Can you with certainty say what
is real or not?
How do you prove that what you
see is real?
Illusion Reveals that
the Brain Fills in Peripheral Vision
What we see in the periphery, just outside the direct focus of the
eye, may sometimes be a visual illusion, according to new findings (The
Uniformity Illusion - Central Stimuli Can Determine Peripheral
It was published in
Psychological Science, a journal of the
Association for Psychological Science.
The findings suggest that
even though our peripheral vision is less accurate and detailed than
what we see in the center of the visual field, we may not notice a
qualitative difference because our visual processing system actually
fills in some of what we "see" in the periphery.
"Our findings show
that, under the right circumstances, a large part of the
periphery may become a visual illusion," says psychology
researcher Marte Otten from the
University of Amsterdam, lead
author on the new research.
"This effect seems to
hold for many basic visual features, indicating that this
‘filling in' is a general, and fundamental, perceptual
As we go about daily
life, we generally operate under the assumption that our perception
of the world directly and accurately represents the outside world.
But visual illusions of
various kinds show us that this isn't always the case.
the brain processes incoming
information about an external stimulus, we come to learn, it creates
a representation of the outside world that can diverge from
reality in noticeable ways.
Otten and colleagues wondered whether this same process might
explain why we usually feel as though our peripheral vision is
detailed and robust when it isn't.
"Perhaps our brain
fills in what we see when the physical stimulus is not rich
enough," she explains.
"The brain represents
peripheral vision with less detail, and these representations
degrade faster than central vision. Therefore, we expected that
peripheral vision should be very susceptible to illusory visual
experiences, for many stimuli and large parts of the visual
Over a series of
experiments, the researchers presented a total of 20 participants
with a series of images.
The participants focused
on the center of the screen - a central image appeared and then a
different peripheral image gradually faded in.
supposed to click the mouse as soon as the difference between the
central patch and the periphery disappeared and the entire screen
appeared to be uniform.
Marte Otten and colleagues changed the defining
characteristic of the central image in different experiments,
varying its shape, orientation, luminance, shade, or motion.
The results showed that all of these characteristics were vulnerable
to a uniformity illusion - that is, participants incorrectly
reported seeing a uniform image when the center and periphery were
The illusion was less likely to occur when the difference between
the center and periphery was large; when the illusion did occur on
these trials, it took longer to emerge.
Participants indicated that they felt roughly equally sure about
their experience of uniformity when it actually did exist as when it
This suggests that the
illusory experiences are similar to a visual experience based on a
physical visual stimulus.
"The fun thing about
this illusion is that you can test this out for yourself," Otten
says. "If you look up the illusion on
www.uniformillusion.com you can
find out just how real the illusory experience feels for you."
"The most surprising is that we found a new class of visual
illusions with such a wide breadth, affecting many different
types of stimuli and large parts of the visual field," Otten
"We hope to use this
illusion as a tool to uncover why peripheral vision seems so
rich and detailed, and more generally, to understand how the
brain creates our visual perceptual experiences."