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Abstract

When approaching a landing site flies extend their legs in order to prevent crash-landing (Goodman 1960). This reflex has been analysed with respect to the underlying release mechanism. Pattern expansion in front of a tethered fly can mimic an approach towards a landing site. Under these conditions landing is a rather stereotyped motor pattern. Only the latency of the onset of the landing response varies with the stimulus strength (Borst 1986). Quantitative studies of the stimulus-latency relationship led to the formulation of a simple model which describes the way movement information at the fly’s retina is processed in order to release landing (Borst and Bahde 1986, 1988b). We propose that the output of local movement detectors sensitive for front-to-back motion in each eye are pooled and subsequently processed by a leaky integrator. Whenever the level of the leaky integrator reaches a fixed threshold landing is released.