Researchers Find an Answer to Galileo's Illusion

Brain researchers have now found an answer to Galileo's optical illusion.

Back in the Sixteenth Century, Galileo Galilei noticed that cosmic bodies seem to change their size depending on how the observer was looking at them. Venus to a naked eye looked eight-ten times bigger than Jupiter, even though the latter is actually much bigger. Also, Venus seems to bask in a radiant glow when seen without a telescope.

Galileo knew that the lens in the telescopes wasn't changing the size of the planets. He described the illusion as "impediment of our eyes."

"Either because their light is refracted in the moisture that cover the pupil, or because it is reflected from the edges of the eyelids and these reflected rays are diffused over the pupil, or for some other reasons," Galileo wrote, according to The Independent.

Later, Hermann von Helmholtz-the 19th Century German physician-physicist-said that there was "something else" that explained the observation, according to a press release.

Researchers at State University of New York College of Optometry have now found that light sensitive cells in the eye respond differently to white and dark objects. The brain then tweaks images; making white objects looking bigger against a dark background than the same-sized black object on a white background.

The difference in how the brain responds to objects in dim light might also explain why reading in low-light conditions might be bad for eyes.

In the study, researchers looked at the 'on' neurons that respond to light images and 'off' neurons that respond to dark images. They found the 'on' neurons acted in a linear way, meaning that the image didn't get distorted. However, a white image set against a black background almost always looks larger because the 'off' neurons distort the image, Livescience reported.

The study is published in the journal Proceedings of the National Academy of Science.