Adaptive strategies in fly vision: On their image-processing qualities

Two adaptive strategies in the fly visual system are discussed. The first strategy consists of considerable intensity processing at the retinal level: intensities over a range of five log units are compressed to a gain variation of the retina cells of about three. The time constants of the retinal system, however, remain constant when intensities vary. This also turned out to be the case when temporal properties of the time courses of the stimuli varied. The authors conclude that at the level of the retina a strong adaptation occurs with respect to the intensity aspects of visual stimuli, whereas the temporal dynamics of this system can be considered almost completely fixed. The second strategy consists of flexibility in the processing of the temporal aspects of stimuli at least at the level of the lobula plate, the highest-order visual ganglion in the fly visual system. The time constants here are tuned by the stimulus and range over more than a factor 10. It is shown that this property is located in the column of one or more ganglia and suggested that it might have a blur-minimizing effect in the processing of moving patterns. This hypothesis was confirmed by a simulation in an artificial receptor array. The flexibility property may, in a general sense, improve the processing of moving images.