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Human eye movements for vision are remarkably adaptable

Press Trust of India  |  Washington 

Humans experience a remarkably fast and spontaneous adjustment of eye movements to create a picture of their surroundings, a new study has found.

When something gets in the way of our ability to see, we quickly pick up a new way to look, in much the same way that we would learn to ride a bike, according to researchers from the University of Southern California.

Our eyes are constantly on the move, darting this way and that four to five times per second. Now researchers have found that the precise manner of those eye movements can change within a matter of hours.

This discovery may suggest a way to help those with macular degeneration better cope with vision loss.

"The system that controls how the eyes move is far more malleable than the literature has suggested," said Bosco Tjan of the University of Southern California.

"We showed that people with normal vision can quickly adjust to a temporary occlusion of their foveal vision by adapting a consistent point in their peripheral vision as their new point of gaze," Tjan said.

The fovea refers to the small, center-most portion of the retina, which is responsible for our high-resolution vision. We move our eyes to direct the fovea to different parts of a scene, constructing a picture of the world around us.

In those with age-related macular degeneration, progressive loss of foveal vision leads to visual impairment and blindness.

In the new study, researchers simulated a loss of foveal vision in six normally sighted young adults by blocking part of a visual scene with a gray disc that followed the individuals' eye gaze.

Those individuals were then asked to complete demanding object-following and visual-search tasks. Within three hours of working on those tasks, people showed a remarkably fast and spontaneous adjustment of eye movements.

Once developed, that change in their "point of gaze" was retained over a period of weeks and was reengaged whenever their foveal vision was blocked.

Tjan and his team said they were surprised by the rate of this adjustment. They noted that patients with macular degeneration frequently do adapt their point of gaze, but in a process that takes months, not days or hours.

They suggested that practice with a visible gray disc like the one used in the study might help speed that process of visual rehabilitation along. The study also found that the oculomotor (eye movement) system prefers control simplicity over optimality.

The study was published in the Cell Press journal Current Biology.

First Published: Sat, August 17 2013. 12:00 IST