How brain processes what eyes see

June 3rd, 2009 - 3:00 pm ICT by ANI  

Washington, June 3 (ANI): Shedding new light on how the brain processes what the eyes see, scientists have found that although visual input obtained during eye movements is being processed by the brain, but it is blocked from awareness.

And thus, researchers at the Center for Molecular and Behavioral Neuroscience (CMBN) at Rutgers University in Newark feel that there is a need to develop a new framework for understanding “perceptual stability”, and how we actually see the world.

Seeing requires the eyes to move, so that light can hit the photoreceptors at the centre of each retina, which then pass that information to the brain.

However, if one is aware of the stimulus that passes before the eyes during the two to three times they move every second, vision would consist of a series of sensations of rapid motion rather than a stable perception of the world.

And current theory has claimed that in order to achieve perceptual stability, visual information gained during an eye movement is eliminated, as if cut off by a camera’s shutter, and removed from processing.

But, in the new research, assistant professor Bart Krekelberg and post-doctoral researcher Tamara L. Watson has shown that theory of saccadic suppression is incorrect.

Instead, the brain is processing information gained during eye movement but blocking it from being reported.

“Rather than completely suppressing inputs during eye movements, the brain is processing that as information it does not need to report back to awareness,” said Krekelberg.

The researchers obtained the findings by making use of a visual illusion in which the presentation of a horizontal line makes a subsequent circle look like an ellipse.

In the new study, the line was presented to research participants immediately before an eye movement.

The researchers observed that while the participants did not recall seeing the line, the image they reported seeing was not a circle but rather an ellipse-it means that they experienced the illusion despite being unaware of the line that causes the illusion.

Watson said: “Although they did not recall seeing the line, the brain apparently did process the line. What this shows is that perceptual stability is not accomplished by suppressing stimuli encountered during an eye movement, or removing them from processing, but rather that those signals are prevented from reaching awareness at a later stage of processing. Some suppression is also happening, but suppression is not enough to explain perceptual stability; it is not the whole story.”

The researchers speculated that one reason why the brain does not discard visual input during eye movements could be that it provides useful information about eye movements.

The findings also show that a new approach is needed to gain additional understanding into the cognitive and neural functions involved in visual processing and perceptual stability.

A better understanding of such changes in processing could pave the way for earlier detection and more effective treatments for those who suffer from deficits associated with eye movements.

The study has been published in the journal Current Biology. (ANI)

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