A remarkable property of many visual systems is the capacity to abstract the direction, velocity and position of a moving target. Detection occurs over a wide range of velocities, stimulus configurations and lighting conditions. Although the neuronal apparatus of visual motion detection has been studied intensively for over 30 years, the mechanism is still unknown. A major impediment to our current understanding is an absence of both measurements and realistic theoretical constructs regarding the synaptic processes by which a network of visual interneurons can compute the direction and velocity of a moving target. In this respect, arthropods, particularly large crustaceans like crayfish, provide a favorable model for a combined experimental and theoretical approach to the problem. Our studies indicate that a mechanism can be resolved into interactions among four classes of identified neurons.
