Theres more than meets the eye in judging the size of an object
Neuroscientists from the University of Washington and the University of Minnesota have found that the first area in the cortex of the human brain that receives information from the eyes processes the perceived size, rather than the actual size, of an object.
"Our eyes only tell us part of what we need to be able to see. The other part is done by the brain, taking the input from the eyes and making guesses or inferences about whats out there in the enviro You cant always trust your eyes. nment. Usually these inferences are very accurate, but sometimes they lead us astray in the form of visual illusions," said Scott Murray, a UW assistant psychology professor and lead author of a study published in the current issue of Nature Neuroscience.
Murray and his Minnesota colleagues, Huseyin Boyaci and Daniel Kersten, used functional magnetic resonance imaging (fMRI) to see how the brain processes the size of objects when faced with an illusion such as the long-known moon illusion. For centuries it has been known that the moon, while rising, looks huge when it is near the horizon and smaller when high in the sky. It is in reality always the same size.
The researchers used a similar illusion, one that looked at the perceived difference in the size of an object at different distances. For their experiment they placed two identical spheres decorated with a checkerboard pattern in the front and rear of a receding brick hallway. In this kind of illusion, the more distant object appears to occupy a larger portion of the visual field.
Using fMRI, the researchers examined how the brains of five people with normal vision registered this difference in perceived size.
They found that the brain region known as the primary visual cortex, which is the first area in the cortex to receive input from the retina, showed a difference. Even though both spheres occupied exactly the same size on the retina, the rear sphere activated an approximately 20 percent larger area in the primary visual cortex than the front sphere. This difference closely matched a perceptual difference in size made by the subjects. Asked about the size of the two spheres, the people estimated the back sphere to be about 20 percent larger than the front one.
Murray said the simplicity of the results can belie its importance to anyone not involved in vision research.
"It almost seems like a first grader could have predicted the result. But virtually no vision or neuroscientist would have. The very dominant view is that the image of an object in the primary visual cortex is just a precise reflection of the image on the retina. Im sure if one were to poll scientists, 99 percent of them would say the large moon and the small moon occupy the same amount of space in the primary visual cortex , assuming they havent read our paper!"
Murray said such illusions are more than simple curiosities because they can help identify how the visual system works.
"Our finding is important because it demonstrates that the process of making inferences about visual properties in our environment is occurring in the earliest stages of the visual system," he said. "Researchers have long believed that the visual system is organized hierarchically, with early visual areas such as the primary visual cortex simply registering the physical input from the eyes and higher visual areas attempting to put all the information together. This work challenges these theories of the organization of the visual system."
Joel Schwarz | EurekAlert!
The most recent press releases about innovation >>>
Die letzten 5 Focus-News des innovations-reports im Überblick:
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...