November 2, 2012
When It Comes To Vision, Our Brain May Be More Important Than Previously Believed
Alan McStravick for redOrbit.com - Your Universe Online
Consciousness and perception have long been understood as being interlinked. But our perceptions may be related less to our sense of sight than was previously understood.
A new study by researchers at the University of Virginia shows that vision may be less important to our ability to see than is the brain´s ability to process the individual points of light we encounter into more complex images. Their study of the fruit fly´s visual system was recently published in the online journal Nature Communications.
In their study, they found the fruit fly larvae, with their very simple eye structure that consists solely of 24 total photoreceptors, provides just enough input to allow the animal´s brain, relatively large by contrast, to assemble the visual or light input into individual images. The human eye has more than 125 million photoreceptors. The results of this study may lead to important advances in the understanding of human consciousness in the future.
“It blows open how we think about vision,” said Barry Condron, a neurobiologist in U.Va.´s College of Arts & Sciences, who oversaw the study. “This tells us that visual input may not be as important to sight as the brain working behind it. In this case, the brain apparently is able to compensate for the minimal visual input.”
Assisting Condron with his study were graduate students Elizabeth Daubert, Nick Macedonia and Catherine Hamilton. They conducted several experiments that aimed to test the vision of the fruit fly larvae when they had noticed an interesting behavior in a previous study of the insect on its nervous system. In that study, they had learned that a larva, tethered to the bottom of a Petri dish and struggling to release itself, would attract other larvae to it by its movement.
The team was able to determine the attraction to and movement towards the tethered larva was not a by-product of touch, through vibration or hearing, but rather was sensed through sight, as the other larvae would move their heads in a side-to-side scanning motion. This attraction to the tethered larva and its writhing motion was particularly interesting to the team because the genetically simple and limited vision of the fruit fly larvae leaves it practically blind.
“The answer must be in the large, somewhat sophisticated brain of these animals,” Condron said. “They are able to take just a couple dozen points of light and then process that into recognizable images; something like when an astronomer with a small telescope is able to use techniques to refine a limited image into useful information about a star.”
Condron and his team have reason to believe that the fruit fly larvae are able to, through a rapid scanning motion with their heads, perceive several light points that their brains are then able to assemble into a sort of panoramic image that becomes clear enough for the individual larva to “see.”
To bolster this theory, the team devised a test for the larvae by producing a video of a writhing larva. The video would remove the sense of vibration and smell from the equation. When they presented the video to test larvae they found they were able still to detect and seek out the struggling larva. Additionally, the team found that if they slowed or sped up the video, the test larvae were less likely to be attracted to the video larva. Other factors, such as a dead real larva or a tethered larva of another species would not attract the test larvae. The team also learned that test larvae had difficulty finding the tethered larva in testing conducted in near darkness.
“Apparently they are — to a very high degree — visually sensitive to detail and rate of motion and can recognize their own species in this way,” Condron said. “This provides us with a good model for trying to understand the role that the brain plays in helping organisms, including humans, to process images, such as recognizing faces.”
What Condron and his team were able to discern was that the scanning motion of the test larvae played an important and significant role in helping them to compose the several visual inputs into one singular image for the brain to process. This would be similar to a human viewing several individual pixels and then relying on the brain to form it into the larger picture. In fact, Condron points out that persons with limited vision tend to use a similar scanning method for collecting a “picture” from very dim light sources. Also of interest is how individuals who have received experimental retinal implants will also use a scanning motion with their heads so that they might take in enough light to form a mental image of the object they are trying to view.
“It´s easy for lab biologists to view fruit flies as simple animals that just feed and reproduce, but we are beginning to realize that that may be in contradiction to the big brain,” Condron said. “There´s more to what they are able to do than previously thought, whether using that brain for behaviors or for constructing images from a limited visual system.”
The reason the fruit fly is an important study specimen is because its neurons bear a striking similarity to the human neural system. While the fruit fly has only about 20,000 neurons, compared to approximately 100 billion in the human, researchers are, according to Condron, within a year of mapping the entirety of fruit fly´s entire nervous system. This landmark will bring researchers only that much closer to achieving a greater understanding of how neurons are able to operate, not only in simpler organisms, but in humans, as well.
Image 2 (below): The simple eyes of fruit fly larvae provide just enough visual input to allow the animal´s brain to assemble images.