Figure-ground discrimination by relative movement in the visual system of the fly Part II: Towards the neural circuitry

A moving object can be separated from its surround on the basis of motion information alone. It has been known for some time that various species and especially the housefly can discriminate relative motion of an object and its background, even when the two have an identical texture. An earlier paper (Reichardt and Poggio, 1979) has analyzed on the basis of behavioural experiments the main features of the algorithm used by the fly to separate figure from ground. This paper (a) proposes the basic structure of a neuronal circuitry possibly underlying the detection of discontinuities in the optical flow by the visual system of the houseflyMusca; (b) compares detailed predictions of the model circuitry with old and new behavioural experiments onMusca (measuring its attempts to fixate an object), and (c) studies the neuronal realization of the model circuitry in terms of electrophysiological recordings from the lobula plate horizontal cells of the blowfly Calliphora