The results are a big step toward producing a bionic eye employing a unique computer chip that can be programmed to do visual processing just like the retina. The chip, called a Cellular Neural Network (CNN) Universal Machine, was invented in 1992 by Roska's father, Tams Roska, and Leon O. Chua, a professor of electrical engineering and computer sciences at UC Berkeley.
"The biology we are learning is going into improving the chip, which is getting more and more similar to the mammalian retina," Roska said. "Nevertheless, a bionic eye is a far-fetched notion until someone figures out how to connect it to the neural circuitry of the brain."
Over a period of nearly three years, Roska painstakingly measured signals from more than 200 ganglion cells in the rabbit retina as he flashed pictures of a featureless square or circle. Ganglion cells are the eye's output cells, forming the optic nerve connecting it to the brain.
"We made very simple measurements on retinal cells, recording excitation and spiking when we flashed squares and moving spots in front of the eye," Roska said.
From these, he and Werblin determined that there are about a dozen different populations of ganglion cells, each spanning the full visual space and producing a different movie output.
One group of ganglion cells, for example, only sends signals when it detects a moving edge. Another group fires only after a stimulus stops. Another sees large uniform areas, yet another only the area surrounding a figure.
"Each representation emphasizes a different feature of the visual world an edge, a blob, movement and sends the information along different paths to the brain," Werblin said.
The two researchers shared these detailed findings with software designer David Balya in Hungary, who modeled the visual processing on a computer, a preliminary step before ac
Contact: Robert Sanders
University of California - Berkeley