How Galileo`s visual illusion works in the mind`s eye revealed

Washington: Researchers have studied a visual illusion that was first discovered by Galileo Galilei, and found that it occurs because of the surprising way our eyes see lightness and darkness in the world.

The work was done by Jens Kremkow and collaborators in the laboratories of Jose Manuel Alonso and Qasim Zaidi at the State University of New York College of Optometry. Galileo was puzzled by the fact that he appearance of the planets hanged depending on whether one looked with the naked eye versus with a telescope. Viewed directly, planets seemed "expanded" and had "a radiant crown", which made Venus looked eight to ten times larger than Jupiter even if Jupiter was four times larger. Though Galileo realized this size illusion was not created by the object-but by his eyes-he did not understand why or how. He mused, "Either because their light is refracted in the moisture that covers 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 reason." Kremkow and colleagues` new study illuminated the scope of the problem. It`s a feature of how we see everything, no less. By examining the responses of neurons in the visual system of the brain-to both light stimuli and dark stimuli-the neuroscientists discovered that, whereas dark stimuli result in a faithful neural response that accurately represents their size, light stimuli on the contrary result in non-linear and exaggerated responses that make the stimulus look larger. So white spots on a black background look bigger than same-sized black spots on white background, and Galileo`s glowing moons are not really as big as they might appear to the unaided eye. The study has been published in the Proceedings of the National Academy of Science.