Neuroscientists have finally solved the mystery behind an optical illusion first described by the astronomer Galileo Galilei. The optical illusion in question causes Venus to appear larger than Jupiter in certain situations.
When Galileo was observing the planets Venus and Jupiter, he noticed that the relative size of both planets changed depending on how they were viewed. Under a telescope, an observer will be able to accurately determine that Jupiter is larger than Venus. When viewed with the naked eye, however, Venus may appear to be around 8 to 10 times larger than Jupiter due to a bright crown around Venus.
Even back then, Galileo already recognized the fact that what he was seeing was an optical illusion. He came up with possible explanations for the illusion involving the refraction and reflection of light in and around the human eye. The problem has been mulled over by numerous scientists throughout the years, but it was the German doctor/physicist Hermann von Helmholtz who first theorized that the phenomenon was not related to blurring and other optical effects. However, Helmholtz failed to come up with a suitable explanation for the phenomenon.
A team of neuroscientists from the State University of New York now has discovered that the illusion is caused by the way our eyes perceive bright and dark objects. Jose Manuel Alonso, Qasim Zaidi and their colleagues authored the study, which was published at the online journal Proceedings of the National Academy of Science. Alonso, who was the lead researcher in the study, is a neuroscientist from the State University of New York's College of Optometry
"This recent discovery resonates with Galileo and Helmholtz's pioneering observations that visual spatial resolution is higher for darks than lights," said Alonso and his colleagues.
The team studied the way neurons connected to the visual sections of the brain worked. By looking at how these brain cells reacted to light and dark stimuli, the team was able to determine that the brain could accurately visualize the size of a dark object. For a bright object, however, the brain can be fooled into seeing a larger and exaggerated version of the object. This non-linear response can make dark objects in bright backgrounds look smaller than bright objects in dark backgrounds.
"Light and dark stimuli are separately processed by ON and OFF channels in retina and thalamus," added Alonso and his team. "Although most textbooks assume that ON and OFF visual responses are relatively balanced throughout the visual system, recent studies have identified a pronounced overrepresentation of OFF responses in the cerebral cortex."
The study has proven that Galileo's optical illusion is caused by the way neurons interact with the eye and the rest of the brain. This discovery debunks earlier theories involving refraction, reflection and the blurring of objects as seen by the naked eye.
