Horace Barlow was at UC Berkeley in 1965 when he and colleague William Levick noticed that some cells in the retina of rabbits fired only when a light moved through the eye's field of view. A stationary light generated minimal response from these cells except when blinking on or off.
In further experiments at UC Berkeley and, later, Cambridge University, Barlow showed that some cells fire only when a target moves from left to right, others fire only when a target moves right to left, and still others respond only to up-down or down-up movement. These cells activate the four sets of muscles that control eye movement and allow close tracking of moving objects. But the signals also make their way through the optic nerve to the brain, providing dynamic detail of the physical world.
Since these early experiments, scientists have discovered cells in the retina that respond best to moving edges or to moving edges of a particular orientation. There may be a dozen or more types of these specialized ganglion cells. The cells' axons - the outgoing wires of the neuron - bundle together to form the optic nerve that funnels visual information to the brain. Werblin and his laboratory colleagues have been probing these cells in the retina, and building computer models that help them understand how the physical world is reconstructed by the eye and the brain into a picture of our surroundings. Their findings have gone into the design of a bionic eye that employs a unique computer chip that can be programmed to do visual processing just like the retina.
Barlow's original explanation of why directionally selective cells fire only in response to movement in one direction were very general, and recent experiments have confused the picture even more. The UC Berkeley team has laid out nearly the whole cir
'"/>
Contact: Robert Sanders
rls@pa.urel.berkeley.edu
510-643-6998
University of California - Berkeley
27-Nov-2002