The primary visual cortex decides how we see the world

Last Updated: Dec 07, 2010, 00:00 AM IST

London: A small part of our brain actually decides how we view the world, says a new study.

The primary visual cortex, the area at the back responsible for processing what we view around us, is known to vary in size by up to three times from one individual to the next.

This affects the way we see the world, meaning we all see the world differently researchers say, reports the journal Nature Neuroscience.

Samuel Schwarzkopf of the University College London said: "Our work is the first to show that the size of part of a person`s brain can predict how they perceive their visual environment," reports the Daily Mail.

The team showed a series of optical illusions to a group of healthy volunteers.

In a second experiment called the `Ponzo` illusion the volunteers were shown two identically sized circles superimposed onto the image of a tunnel where the circle placed further back appears larger than that placed near the front.

By adapting these illusions, the researchers were able to show that individual volunteers saw the illusions differently.

Most people will see the first circle as smaller than the second one even though they are both the same size.

For example, some people saw a big, although illusory, difference in size between the two circles, but others barely saw any difference in apparent size.

Using brain scans researchers were also able to measure the surface area of the primary visual cortex in each volunteer and found a great deal of variability in the size of this area.

Surprisingly, there was a strong link between its size and the extent to which volunteers perceived the size illusion - the smaller the area, the more pronounced the visual illusion.

IANS