The Bigger It Is, the Harder to See

Larger, brighter objects more difficult for humans to track with their eyes

(HealthDay is the new name for HealthScoutNews.)

FRIDAY, July 18, 2003 (HealthDayNews) -- You'd assume that the larger and brighter an object, the easier it is for your eyes to follow its movement.

But a Vanderbilt University study in this week's issue of Nature says the opposite is true. The bigger and brighter an object, the harder it is for you to perceive its motion.

This unexpected finding is due to the way in which visual signals are processed in the part of the brain called the medial temporal visual area. It's one of more than 30 cortical centers in the brain involved in processing visual signals.

The study offers new information about one of the most sophisticated processes performed by the brain: identifying and tracking moving objects.

"The bigger an object, the easier it is to see. But it is actually harder for people to determine the motion of objects larger than a tennis ball held at arm's length than it is to gauge the motion of smaller objects," study author Duje Tadin says in a news release.

He and his colleagues discovered this when they analyzed the results of a series of psychosocial experiments. In these tests, people were asked to determine the direction of motion of patterns of varying speed, size and contrast that were flashed briefly on a screen.

Those experiments revealed that humans have more trouble determining the motion of larger objects. The tests also showed that this effect was greatest in conditions of high contrast.

More information

Here's where you can learn more about eyes and vision.

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