How two eyes see one image

The Wisconsin-Madison team found the point in the human brain where the vision of two eyes unites, at which the transformation to a cyclopean view of the world takes place, using prisms and an advanced brain scanner. The findings may help in the treatment of vision problems like amblyopia, or lazy eye.

If you have two working eyes, you are live streaming two images of the world into your brain. The brain combines the two to produce a view of the world that appears as though you had a single eye.

"If you're reaching out with your hand, you want to aim not at where things appear to be, but where they are," said Bas Rokers, psychology professor at the University of Wisconsin-Madison.

"Two eyes are giving you two images that don't by themselves tell you where things are relative to your hand. It's the integrated information that tells you where things are," Rokers said in Current Biology.

A group of neurons in the visual cortex called the striate cortex, or V1, is handling two sets of pictures from our eyes -- one view each from the left eye and the right eye. The researchers tucked people in functional magnetic resonance imaging (MRI) machines, and had them peer into a prismatic device that showed each eye a different image.

"The brain processes the two presented images like it would with any normal pair of images, and perceives them as a single bar in the centre of the field of vision, but shifted slightly backwards in depth," Rokers said.