The Mind’s Eye
Psychologists study visual perception
By Eva Emerson
USC College vision researcher Bosco Tjan holds up his cell phone and asks “What is this?”
This is Tjan’s way of paying ode to the human visual system, from the
pupil and retina to the visual processing areas in the cortex of the
brain.
“The best computer vision system can’t do what we do instantly and
without effort,” says Tjan, an assistant professor of psychology. “If
we can understand what happens in your mind’s eye when we see what’s
around us, we can understand the whole brain,” says Tjan. He studies
the initial steps of seeing and recognition, and how adding specially
designed visual “noise” to an image impacts its recognizability.
This could lead to new insights into the brain and help people who rely
on peripheral vision, where these effects are most pronounced.
A Leaping Tiger
“Detecting the motion of prey or predators is critical for survival of
all animals,” says Zhong-Lin Lu, associate professor of psychology, who
studies how we sense motion. “If you see a tiger, the brain can tell if
it is moving by comparing the luminosity, texture and color of the
tiger to the background.”
“The brain breaks motion down into these three parts, analyzes the
information by three different pathways, and then puts it all back
together. We see the sum—one tiger moving,” says Lu. He will use the
College’s new brain imaging center to pinpoint where in the brain these
processes take place.
Pleasure of Perception
An expert on eye and brain, Irving Biederman, the Harold W. Dornsife
Professor of Neuroscience, delights in the vagaries of
vision—especially those that reveal seeing as a product of the mind as
much as that of the eye. When you move your eyes the mind suppresses
vision temporarily, so that you can never look at things while your
eyes roam. “The mind fills in the blanks,” says Biederman. Recently, he
started investigating the connections between visual perception,
cognition and pleasure to understand why we choose to pay attention to
certain things in our surroundings over others.
The pay-off is pleasure, he thinks. In the cerebral cortex of the
brain, scientists have found cells that release enkephalins—natural
opiates considered the neurochemical basis of pleasure. These cells are
found at all levels of the higher visual system, but are most dense in
brain areas where faces, objects and voices are perceived and linked to
memories.
At the imaging center, Biederman plans to test his theory, and continue to study object recognition.
“Somewhere between 50 to 65 percent of the brain’s cortex is involved
in visual perception,” Biederman says. “We’re a very visual species.”
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