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Abstract

Optomotor thrust responses of the fruitfly Drosophila melanogaster to moving gratings have been analysed in order to determine the arrangement of elementary movement detectors in the hexagonal array of the compound eye. These detectors enable the fly to “perceive” vertical movement. The results indicate that, under photopic stimulation of a lateral equatorial eye region, the movement specific response originates predominantly from two types of elementary movement detectors which connect neighbouring visual elements in the compound eye. One of the detectors is oriented vertically, the other detector deviates 60° towards the anterior-superior direction (Fig. 5b). The maximum of the thrust differences to antagonistic movement is obtained if the pattern is moving vertically or along a superior/anterior — inferior/posterior direction 30° displaced from the vertical (Fig. 3d,e, Fig. 6). Only one of the detectors coincides with one of the two detectors responsible for horizontal movement detection. This indicates that a third movement specific interaction in the compound eye of Drosophila has to be postulated. — The contrast dependence of the thrust response (Fig. 2) yields the acceptance angle of the receptors mediating the response. The result Δϱ coincides with the acceptance angle found by analysis of the turning response of Drosophila (Heisenberg and Buchner, 1977). This value corresponds to the acceptance angle expected, on the basis of optical considerations, for the receptor system R 1–6. — The movement-specific neuronal network responsible for thrust control is not homogeneous throughout the visual field of Drosophila. Magnitude and preferred direction of the thrust response in the upper frontal part of the visual field seem to vary considerably in different flies (Fig. 6).