Humans have an inherent ability to recognize faces and other objects with just a glimpse, and now researchers have found that this ability to visually process images is much faster than it is believed.
Taking advantage of brain mapping in patients about to undergo surgery for epilepsy, researchers at Children's Hospital Boston, have for the first time showed that the brain, at a very early processing stage, can recognize objects under a variety of conditions very rapidly.
Visual information flows from the retina of the eye up through a hierarchy of visual areas in the brain, finally reaching the temporal lobe, which is ultimately responsible for our visual recognition capacity and our visual perceptions.
The temporal lobe also signals back to earlier processing areas and this cross talk solidifies visual perception, revealed the researchers.
"What hasn't been entirely clear is the relative contribution of these "feed-forward" and "feed-back" signals. Some people think that if you don't have feedback, you don't have vision. But we've shown that there is an initial wave of activity that gives a quick initial impression that's already very powerful," said Dr. Gabriel Kreiman, from the Department of Ophthalmology at Children's Hospital Boston and the study's senior investigator.
He further said that although feedback from higher brain areas may occur later and is often important, very fast visual processing would have an evolutionary advantage in critical situations, such as encountering a predator.
Unlike traditional noninvasive brain monitoring, the researchers placed electrodes directly on the brain, and obtained data at extremely high temporal resolution - picking up signals as fast as 100 milliseconds (thousandths of seconds) after presentation of a visual stimulus - and monitor activity in very discrete, specific locations.
The researchers then implanted electrodes in the brains of 11 adolescents and young adults with epilepsy (anywhere from 48 to 126 electrodes per patient) in the areas where their seizures were believed to originate.
While the electrodes recorded brain activity, the patients were presented with a series of images from five different categories-animals, chairs, human faces, fruits and vehicles- of different sizes and degrees of rotation.
The recordings revealed that certain areas of the brain's visual cortex selectively recognize certain categories of objects.
The response was so strong and consistent that the researchers could use mathematical algorithms to determine what patients were viewing, just by examining their pattern of neural responses.
Moreover, these responses occurred regardless of the object's scale or degree of rotation.
The recognition was evident within as little as 100 milliseconds-too fast for information to be relayed from the visual cortex to the temporal lobe and back again.
The findings were published in the journal Neuron.