Motion computation and visual orientation in flies.

1. Visual orientation greatly relies on the evaluation of the motion patterns received by the eyes when the animal moves around. 2. In a combination of behavioral, neurophysiological and pharmacological analysis and modelling, the mechanisms are established by which the visual system of the fly extracts three types of-basic retinal motion patterns. 3. Coherent retinal large-filed motion as is induced during deviations of the animal from its course, image expansion occurring when the animal approaches an obstacle, and relative motion which is induced when a nearby object is passed in front of its background. 4. Separate neuronal networks are specifically tuned to each of these motion patterns and make use of them in three different orientation tasks: in compensatory course stabilization, the control of landing behaviour and the fixation of objects.