Have you ever wondered why we don't see the world as if it were a movie on a TV screen? Many mammals do have a 2D vision. Nevertheless, from shooting or juggling to baseball or driving, hand-eye coordination requires a three dimensional image of the environment. But it was not known how our brains get the 3D picture from 2D retinal images.
A new research seems
to have detected the brain region linked to 3D visual processing. For getting the spacial, 3 D picture, of the environment, primates (humans included) rely on two main visual cues: the slightly different image recorded by each eye (spatial binocular disparity) and the way the perceived shape of an object shifts as it moves.
A team led by Guy Orban of the Catholic University of Leuven in Belgium found that a brain area, the anterior intraparietal cortex (AIP), uniquely sensitive to both these visual cues, integrates this information.
In two separate tests, the brains of monkeys were investigated by functional magnetic resonance imaging (fMRI) while they watched 3D objects.
In the first test, the team checked how motion affected 3D perception. The monkeys watched rotating images of connected lines, like partially unfolded paper clips, that only stayed in the visual field of one eye at a time. In the second approach, the monkeys used both eyes to watch computer simulations of small complex objects, being checked this way the role of the binocular disparity in detecting 3D images. "We found that these different bits of processing converged on one brain region: the AIP," said Orban.
The AIP was already connected to the visual control of hand movements, like picking up things. The need of "reach and grasp" movements is unique to primates, that's why the team thinks it evolved after primates split off from other mammals. "I'd expect this brain region to be unique to primates and to have evolved in parallel with hands and frontal eyes," said Orban.
"This study considerably broadens the processes we think the AIP is involved in," said Andrew Parker, a neuroscientist at the University of Oxford, U.K., expert in binocular perception.
Still, Parker also mentions that the monkeys were able to move their hands during the research, and this could have activated the AIP area somewhat as well; this, however, does not change the importance of the discovery. "If this research holds up, it will cause me to change my views on depth perception.", Parker said.