Researchers have explained an optical illusion first noticed by Galileo Galilei.
Galileo was the first to notice a difference in the way planets appeared when looking through them either with the naked eye or a telescope; researchers found it has to do with the way the eyes process light and dark, a State University of New York College of Optometry news release reported.
The finding could help researchers gain insight how the brain looks at both black and white objects.
When viewed with the naked eye planets appear to "expand" and be surrounded by "a radiant crown," the news release reported. This phenomenon causes Venus to appear eight to ten times larger than Jupiter despite the fact that Jupiter is four times bigger physically.
Galileo acknowledged that the planets' appearance was caused by an optical illusion, but did not understand how it worked.
"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," he said.
In the past researchers have agreed the illusion was most likely caused by a "blur" or something similar. Blur does have the ability to distort size, but would not explain why Venus looks larger than Jupiter when viewed with the naked eye.
Nineteenth century German Physicists Hermann von Helmholtz was the first to realize blur could not fully explain the phenomenon.
The recent study looked at how neurons in the visual system of the brain responded to "both light stimuli and dark stimuli," the news release reported.
The team found "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," the news release reported.
This would explain why white spots against a black background would look larger the spots of the same size but of inverse colors.
The finding suggests the illusion originates in the photoreceptors of the eye, which are the basis of sight.
