VISUAL-ACUITY FOR MOVING-OBJECTS IN FIRST-ORDER AND 2ND-ORDER NEURONSOF THE FLY COMPOUND EYE

The early stages of visual systems contain a Variety of components tha t limit both the spatial resolution and the temporal resolution of vis ion. When an animal sees a moving object, or moves relative to its env ironment, both spatial and temporal factors contribute to its ability to resolve the movement. In the present work we have combined currentl y available knowledge about the early stages of fly vision (optical sy stem, photoreceptors, and large monopolar cells) to predict the resolu tion of the first two cell layers to moving point objects. These calcu lations included recent measurements of nonlinear light responses. Bec ause background light level has a strong effect on the temporal behavi or of these early visual layers, we examined the effects of light leve l on motion resolution. We also studied the effect of position within the eye, which is known to affect the static resolution of vision. Our results indicate that responses in large monopolar cells to moving po int objects are maximal at angular velocities of 100-200 degrees/s. Th e resolution of point objects by both these early stages of the visual system is similar from stationary to an angular velocity of similar t o 200 degrees/s. Above this, resolution deteriorates approximately lin early with velocity.