5 Optic Flow Processing in the Cockpit of the Fly

Abstract

Flies are known for their acrobatic maneuverability which enables them, for example, to chase mates at turning velocities of more than 3000 deg/sec with delay times of less than 30 msec (Land and Collett 1974; Wagner 1986a,b,c). It is this fantastic behavior that has initiated much research both on its sensory control and on the biophysical and aerodynamic principles of the flight output (Dickinson et al. 1999Dickinson et al. 2000). In particular, the fly served as one of the model organisms leading to the development of the Reichardt model for elementary motion detection, one of the most influential and successful models in computational neuroscience up until today. Here, we review the current state of knowledge about the neural processing of optic flow that represents one sensory component intimately involved in flight control. Unless stated otherwise, all data presented in the following were obtained on the blowfly Calliphora vicina, which we will often casually refer to as “the fly.”

THE FLY VISUAL SYSTEM
The processing of visual motion starts in the eye. In flies, as in most invertebrates, this structure is built from many single elements called facets or ommatidia. Each ommatidium possesses its own little lens and its own set of photoreceptors. The latter send axons into a part of the brain exclusively devoted to image processing called the “visual ganglia.” In flies, the visual ganglia consist of three successive layers of neuropile where the columnar composition reflects the relative position of facets within the eye. Thus, visual images perceived by the...