05/19/2004 07:00:00

The Brain Can Make Errors in Reassembling the Color and Motion of Objects

PASADENA, Calif.—You're driving along in your car and catch a glimpse of a green SUV out of the corner of your eye. A few seconds later, you glance over, and to your surprise discover that the SUV is actually brown.

You may assume this is just your memory playing tricks on you, but new research from psychophysicists at the California Institute of Technology and the Helmholtz Institute in the Netherlands suggests that initial perceptions themselves can contain misassigned colors. This can happen in certain cases where the brain uses what it sees in the center of vision and then rearranges the colors in peripheral vision to match.

In an article appearing in this week's journal Nature, Caltech graduate student Daw-An Wu, Caltech professor of biology Shinsuke Shimojo, and Ryota Kanai of the Helmholtz Institute report that the color of an object can be misassigned even as observers are intently watching an ongoing event because of the way the brain combines the perceptions of motion and color. Because different parts of the brain are responsible for dealing with motion and color perception, mistakes in "binding" can occur, where the motion from one object is combined with the color of another object.

This is demonstrated when observers gaze steadily at a computer screen on which red and green dots are in upward and downward motion. In the center area of the screen, all the red dots are moving upward while all the green dots are moving downward.

Unknown to the observers, however, the researchers are able to control the motion of the red and green dots at the periphery of the screen. In other words, the red and green dots are moving in a certain direction in the center area of the screen, but their motion is partially or even wholly reversed on each side.

The observers show a significant tendency to mistake the motion of the red and green dots at the periphery. Even when the motion was completely reversed on the sides, the observers would see the same motion all across the screen.

According to Wu, the lead author of the paper, the design of the experiment exploits the fact that different parts of the brain are responsible for processing different visual features, such as motion and color. Further, the experiment shows that the brain can be tricked into binding the information back together incorrectly.

"This illusion confirms the existence of the binding problem the brain faces in integrating basic visual features of objects, " says Wu. "Here, the information is reintegrated incorrectly because the information in the center, where our vision is strongest, vetoes contradicting (but correct) information in the periphery."

The title of the article is "Steady-State Misbinding of Color and Motion."

 

 

Written by Robert Tindol