Figure-ground discrimination in the visual system of Drosophila melanogaster

Drosophila melanogaster is able to detect a small visual object hidden in a background of identical texture, as long as there is relative motion between their retinal images. The properties of figure-ground discrimination in the walking fly are studied under experimental conditions where the positions of figure and ground oscillate sinusoidally with similar frequency and similar amplitude but with different phase. The following points have been established. (a) The average turning reaction of the stationarily walkingDrosophila depends on phase; contrary to results obtained with the flyingMusca (Reichardt and Poggio, 1979), antiphasic oscillation of figure and ground does not suppress the attrativeness of the figure. (b) A translatory response has been found which also depends on the phase difference of the oscillatory movements of figure and ground. (c) The time course of the responses and its intra- and inter-individual variability do not seem to fit into a rigid model of figure-ground discrimination