Brain’s Center for Perceiving 3-D Motion Is Identified

July 21, 2009

AUSTIN, Texas — Ducking a punch or a thrown spear calls for the power of the human brain to process 3-D motion, and to perceive an object (whether it's offensive or not) moving in three dimensions is critical to survival. It also leads to a lot of fun at 3-D movies.

Neuroscientists have now pinpointed where and how the brain processes 3-D motion using specially developed computer displays and an fMRI (functional magnetic resonance imaging) machine to scan the brain.

Bas Rokers
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).Brain rendering by Thadeus Czuba
Photo by Marsha Miller

They found, surprisingly, that 3-D motion processing occurs in an area in the brain—located just behind the left and right ears—long thought to only be responsible for processing two-dimensional motion (up, down, left and right).

This area, known simply as MT+, and its underlying neuron circuitry are so well studied that most scientists had concluded that 3-D motion must be processed elsewhere. Until now.

"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. (Watch a video illustration of this process. Video opens in a new window on YouTube.)

"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."

Huk, Cormack, and postdoctoral research and lead author Bas Rokers published their findings in Nature Neuroscience online the week of July 7. They are members of the Institute for Neuroscience and Center for Perceptual Systems.

The research was supported by a National Science Foundation CAREER Award to Huk.

For more information, contact: Lee Clippard, Lady Bird Johnson Wildflower Center, 512-232-0104; Dr. Alexander Huk, 512-232-6095.

3 Comments to "Brain’s Center for Perceiving 3-D Motion Is Identified"

1.  David Davis said on July 31, 2009

Have you conducted studies that include people who do not have normal, binocular vision and, if so, what are the implications? I am 60 years old. I began wearing glasses when I was 18 months old. At 16, I wore contact lenses for a short period of time. My vision improved to the point I no longer needed to wear glasses. However, in my mid 20s I became aware that I do not have stereoscopic/binocular vision. I realized I often use one eye or the other at a given time. When I think about it, I am aware of the eye I am using at that time.

2.  Bas Rokers said on Aug. 4, 2009

Hi there, David,

We are in the early stages of designing a study exactly with people who do not have normal binocular vision, specifically with people who had undiagnosed amblyopia during childhood. There is some evidence that vision therapy in adulthood may improve stereo-vision in such people, and we would like to find out why that is, and how that happens.

3.  Randy Eady said on Aug. 20, 2009

Hi David,

Your comment is of keen interest to our research on movement and balance disorders related to CNS dysrythmia.

We are using various techniques such as dynamic, unfocused eye movement to pinpoint deficits in the body's three balance centers and design specific and appropriate remediation protocols.

It is not a surprise to our practitioners that this area of the brain (near the balance labyrinth) is associated with 3-D perception.

In fact, we will not be surprised if a Poly Vagal Nervous system response is also innervated in the limbic brain to allow us to practically smell 3-D form.

Remember, just as you hardly realize which eye is in use, movements felt by our body outside of our audible range are still rhythmic, and serve us much in the same way as audible sound. We sense movement by way of our three body balance centers. These systems all relate fluid to electrical impulse via the central nervous system (brain and spinal cord), the skeletal structure, and the musculature. It is a complex systems that works as a team to provide the right output for proper body stabilization against gravitational forces. Bodily movements and perception in 3-D depend on messages to and from the control room of the brain. The brain remembers patterns of movement via rhythm not of individual muscle interactions. That's one reason why your eye preference selection is so intuitive.

Randy Eady, M.Ed., NCC