News Magazine of the UW Department of Communication
James Brown, COM361
The way that we understand the brain’s processing of color may be fundamentally wrong, neuroscientist Greg Horwitz said yesterday at the University of Washington.
Color processing is a basic process, but one we know little about. We do know that light is passed from the retina to a part of the thalamus region of the brain, then to the primary visual cortex. The thalamus area arranges light very efficiently as each receptor cell can respond one way when exposed to one of two colors, and in an opposite manner when in contact with the other. The primary visual cortex, however, responds to colors seemingly at random; its receptor cells seem to respond to specific hues and amounts of a single color.
Any basic textbook about the brain will indicate spike-triggered stimulation as the method of choice for determining which receptors in the primary visual cortex respond to which color combinations, but Horwitz disagrees. He said that spike-triggered stimulation, which retrieves a cell’s input before it is excited, averages a lot of data together to determine which colors the cell responded to, providing an imperfect result. Horwitz spoke about his new method that tracks where changes happen instead of which changes occur.
Horwitz’s method uses an old statistician’s trick called principle component analysis, which entails finding the largest changes in a set of data. Horwitz uses this model to analyze which areas change as different light patterns are shown while mostly ignoring what those changes are.
Under the spike-triggered stimulation method as well as Horwitz’s principle component analysis, an image is produced that a particular receptor cell should be excited by when viewed. The latter proves more effective than the former and Horwitz thinks he can explain why: though a cell only responds to one color, the degree of that response is determined by the second color coupled with the one causing stimulation.
“Like a transistor, one signal is amplified by the other,” Horwitz said. “It’s interesting here, but I believe it may be in play in other systems as well.”
Around 50 attendees gathered to hear the UW assistant professor and researcher speak about his findings; though the presentation was intended for members of the scientific community, all were welcome. The response was positive, and Horwitz took questions from students in a variety of departments, including, psychology, neurosurgery and English.
“We’re applying new technology to old problems,” Horwitz said. “Long-held assumptions about color research may not be true.”
