Researchers Make New Discovery about How the Brain
Perceives Brightness
HOUSTON - (April 14, 2004)-A researcher at The University of Texas Medical School at Houston has discovered a new visual illusion that sheds light on the way brain cells determine the brightness of objects.
In a paper published in advance online today by Nature , David Eagleman, Ph.D., assistant professor in the Department of Neurobiology and Anatomy, along with colleagues John Jacobson and Terrence Sejnowski at the Salk Institute for Biological Studies, report that time plays an important role in the brain's visual system. With changes in the time that objects appear and disappear, the brain can experience the illusion that the brightness of an object has changed when, in fact, it has not.
"We've discovered a new illusion that addresses how the brain encodes brightness," Eagleman said. "This is another demonstration that visual illusions can serve as a powerful window into the workings of the brain."
It is well known that the brightness of an object depends on its spatial context. For example, bright or dark objects surrounding a gray disc can make the disc appear to be dimmer or brighter. What Eagleman and co-investigators discovered is that brightness also can depend on how those surrounding objects are displayed in time.
Study participants were asked to view two flashing objects on a computer screen. When researchers manipulated the relative timing of the appearance and disappearance of objects, it changed how bright the objects were perceived to be.
"While this is a simple illusion, it struck us as very strange, because there was no theory we knew of that should have predicted this to be true," Eagleman said.
Eagleman and his colleagues extended the illusion-which they call the "temporal context effect"-into predictions about the underlying neural machinery. Specifically, they concluded that there must be at least two interacting populations of brain cells involved in encoding brightness, a hypothesis not previously considered.
"By directly tackling the problem of time in the brain-how time in neural activity interacts with time in the outside world-we can get mileage on many outstanding questions in neuroscience and make surprising new predictions," Eagleman said. Studies of timing could lead to a greater understanding of language disorders, memory and consciousness, he added.
For demonstrations of the illusion, see: http://nba.uth.tmc.edu/homepage/eagleman/TCE
The paper, titled " Perceived luminance depends on temporal context," was selected for publication under the journal's Advance Online Publication program and will appear in the print version at a later date.
Media Contact: Meredith Raine
Media Hotline: 713.500.3030