"Our research suggests that a large set of rich and important functions related to 3-D motion perception may have been previously overlooked in MT+," says Alexander Huk, assistant professor of neurobiology. "Given how much we already know about MT+, this research gives us strong clues about how the brain processes 3-D motion."
For the study, Huk and his colleagues had people watch 3-D visualizations while lying motionless for one or two hours in an MRI scanner fitted with a customized stereovision projection system.
The fMRI scans revealed that the MT+ area had intense neural activity when participants perceived objects (in this case, small dots) moving toward and away from their eyes. Colorized images of participants' brains show the MT+ area awash in bright blue.
The tests also revealed how the MT+ area processes 3-D motion: it simultaneously encodes two types of cues coming from moving objects.
There is a mismatch between what the left and right eyes see. This is called binocular disparity. (When you alternate between closing your left and right eye, objects appear to jump back and forth.)
For a moving object, the brain calculates the change in this mismatch over time.
Simultaneously, an object speeding directly toward the eyes will move across the left eye's retina from right to left and the right eye's retina from left to right.
"The brain is using both of these ways to add 3-D motion up," says Huk. "It's seeing a change in position over time, and it's seeing opposite motions falling on the two retinas."
That processing comes together in the MT+ area.
"Who cares if the tiger or the spear is going from side to side?" says Lawrence Cormack, associate professor of psychology. "The most important kind of motion you can see is something coming at you, and this critical process has been elusive to us. Now we are beginning to understand where it occurs in the brain."
Dr. Alex Huk, a neurobiologist at the University of Texas at Austin, talks about one way that the brain perceives 3-D motion. 3-D motion perception is critical to everyday life and survival. He and his fellow scientists, Bas Rokers and Larry Cormack, discovered that the brain processes 3-D motion in an area called MT+, long thought to only be responsible for processing 2-D motion.
(Photo Credit: Lee Clippard, The University of Texas at Austin)
Drs. Bas Rokers (pictured), Alex Huk and Larry Cormack discovered the center for 3-D motion processing in the human brain, the MT+ area. An enhanced image of Rokers' brain from an fMRI scan shows the MT+ area active when perceiving 3-D motion (bright blue area in the lower left of the photo).
(Photo Credit: Brain rendering by Thadeus Czuba. Photo by Marsha Miller.)
Source: University of Texas at Austin