Werblin and doctoral student Botond Roska determined after nearly three years of work with rabbit retinas that there are about a dozen different populations of ganglion cellsthe eye's output cellssending signals to the brain. One group sends signals only when it detects a moving edge; another, when it sees large uniform areas, and so forth. "Each representation emphasizes a different feature of the visual worldan edge, a blob, movementand sends the information along different paths to the brain," Werblin explains. The brain then interprets the 12 sketches and probably merges them with images from memory, he adds.
"These 12 pictures of the world constitute all the information we will ever have about what's out there, and from these 12 pictures, which are so sparse, we reconstruct the richness of the visual world," Werblin says. "I'm curious how nature selected these 12 simple movies and how it can be that they are sufficient to provide us with all the information we seem to need."
The fact that the process is so pared down, however, may very well help scientists produce bionic eyes, employing a unique computer chip that can be programmed to do visual processing like the retina. Roska's father, Tams Roska, and Leon O. Chua of UC Berkeley invented the chip, called a Cellular Neural Network (CNN) Universal Machine, in 1992. "The biology we are learning is going into improving the chip, which is getting more and more similar to the mammalian retina," Roska says. "Nevertheless, a bionic eye is a far-fetched notion until someone figures out how to connect it to the neural circuitry of the brain."
