It began simply enough nearly two decades ago. When the
professor of psychology wanted to enhance students' learning
experiences in his 300-level class on perception, he introduced some
visual aids digital images of seemingly innocuous geometric
Suddenly, students discovered there's more than meets the eye.
But is there?
In the visual illusion research of psychologist and artist D. Alan
Stubbs, perception and reality can be worlds apart. As a catalyst of
illusion, digital art helps to illustrate principles of perception. It
also raises awareness of the important distinction between physical
and psychological dimensions of stimuli that affect human behavior,
including errors in judgment.
As pilots flying at night without instrumentation and outdoor
enthusiasts caught in whiteouts know all too well, there are times
when our senses deceive us. Or, to put it another way, a dual reality
seems to exist. And that, says Stubbs, gets to the truth of illusions.
"Illusion is something that's not quite the same as you think it
is," says Stubbs, a University of Maine professor of psychology and an
adjunct faculty member in the Department of Art. "For instance, all
photos are illusions. The picture on the paper is not your Uncle
Henry, but light or marks similar to what you see when you look at
him. Put a CD in and the music sounds like whomever. That's an
Some illusory images, like those Stubbs creates, might seem to be
examples of misperception. Instead, Stubbs views them as mechanisms
for understanding how the perceptual process works. That's
particularly important, because perception is a strong influencer of
"Perception is fundamental," he says. "If you can't perceive, where
is cognition going to come from? You perceive, act and know. They
can't be separated. As I study it, perception is directly gathering
information about the world."
Stubbs' research has evolved from the study of time perception
in animals to graph and image perception in humans. It dovetails into
his decades-long passion for photography that began concurrently with
his graduate research. For Stubbs, the science of perception informs
his art and vice versa.
In the 1970s, Stubbs was using pigeons to study perception learning
and behavior, as well as visual cognition. In particular, he explored
how pigeons tell time.
Then, almost a decade ago, Stubbs turned his focus to another form
of perceptual learning.
"I started doing a lot of graph experiments in front of a computer
screen," he says. "That's where I became the pigeon."
With UMaine psychology colleague Laurence Smith, Stubbs studies
graphical perception, or how people extract information from data
graphs to draw conclusions. The psychologists examine the accuracy of
people's graph-based judgments, as well as biases resulting from the
graph formats or the viewers' expectations. They also consider what
pertinent details are needed in graph design to effectively
communicate to produce sound, informed judgments.
The research is similar to Stubbs' work in image perception, which
had its start in the classroom where he sought to bring the perceptual
process to life for his students. Using PhotoShop software, Stubbs
took one-dimensional blackboard drawings and created his own 3D
digital images that not only convey psychological principles of
perception, but give the illusion of increased and decreased
brightness and even movement.
"Students find the images fascinating because of the wow' factor,
but I use them to make points. Even as they seem to deceive us,
illusions give us a good truth about how the visual system works."
After a decade of creating the research-based visual aids, Stubbs
has amassed a collection of original digital art that he now exhibits
for the public. He admits that in the creation process, only one in 10
of his illusion images "turns out." But most important, those that do
lead him to other questions about perception.
"I found I actually learn more about the phenomenon by creating the
images," he says.
One of Stubbs' digital art pieces, Dynamic Luminance-Gradient
Effect, was deemed one of the Top 10 Best Visual Illusions of the Year
in 2006 by the international Vision Sciences Society.
This year, Stubbs teamed with recent Ph.D. student Simone Gori of
the University of Padua to create an image that was used as the logo
for the 2007 Vision Sciences Society conference in May.
Dynamic Luminance-Gradient Effect lines that meet in the center
where a gradation of color or light is apparent "works" by having
the viewer physically move closer to and away from the image. Move
toward the center and the image appears to brighten, giving a "here
comes the sun" effect.
In other images, shaded areas among the bars and lines in his
artwork appear to move, grow or shrink, depending on the distance
between a viewer's eye and the image.
"It is an illusion in that nothing is changing. Nothing is getting
brighter. There is only apparent motion. The illusion has to do with
what's happening across the eye," Stubbs says. "It's not a tricking;
it just looks like the image is brightening when it's not."
Part of the reason such illusions work, says Stubbs, is the retina
receives increasing and decreasing light. Moving closer to a figure
with a brighter center causes a person to see less in the periphery,
while every point on the retina receives more light.
Gradation of the boundaries graded change of luminance appears
to be a key to the illusory effect. "One explanation of this effect
could be that these patterns, with gradients of luminance change,
suggest to our visual system the presence of an optic flow, like a
tunnel with a light at the end," wrote Stubbs and Gori in the journal
In a sense, our visual system misinterprets the image, behaving as
if it were a 3D physical situation instead of a two-dimensional
"All of these illusory effects show the importance of the
distinction between the physical dimension and the psychological
between luminance and brightness," explained Stubbs, writing in High
Resolution, a specialty newsletter for the displays industry. "Without
it, we can make errors in judgment and think that there is a physical
aspect for what we see when, in fact, we are being influenced by
by Margaret Nagle
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