The walleye and the professor

Probing the walleye eye, Dwight Burkhardt pushed the boundaries of human visual science--and the fishing lure industry

Walleyes, with their huge cone cells, were the perfect animal for psychology professor Dwight Burkhardt to study vision. His work also spurred the design of better fishing lures.

Some of the most basic discoveries about how the eye works came from an unlikely alliance between a University psychology professor and that prized predator of Minnesota lakes, the walleye.

Beginning his research more than three decades ago, Dwight Burkhardt wanted to know how the cone cells of the retina responded to light. Cones, the cells that operate during the day, give us color and fine pattern vision. (The other light-responsive retinal cells, the rods, govern night vision.) When Burkhardt discovered that the cone cells of the walleye retina were huge, he set about studying them in his laboratory.

In responding to light, cone cells generate an electrical current. The more intense the light, the stronger the current. But to see how the process works, it was necessary to insert an electrode into an individual cone cell to record its electrical acitivity. Even the walleye cone is only one-fifth the thickness of a human hair, and an electrode had to be much thinner to avoid disrupting the cone's function. By fashioning glass electrodes only 1/250,000th of an inch thick, Burkhardt was able to test the responses of walleye cone cells.

After studying hundreds of cones, he found the walleye had two types: the larger, more common cone responds to orange light, and the other is sensitive to green light. That discovery spurred the design of chartreuse and orange walleye fishing lures. Burkhardt also found that walleyes can see well in dim light, not only because they have lots of rods but because of the tapetum, a reflective layer of cells behind the cones that reflect light back toward the cones and that give the fish its characteristic creamy white glow.

In other experiments, Burkhardt found that when suddenly subject to bright laser light, cones initially don¿t respond but gradually regain that ability. We, too, experience this phenomenon, called light adaptation, when we exit a dark building on a bright sunny day.

With the help of his finny friends, Burkhardt went on to make many discoveries about how cells in the eye respond to different types and patterns of light, laying the groundwork for a comprehensive understanding of vision.