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Abstract

To investigate the optomotor leg responses ofDrosophila melanogaster the free walking fly is kept in stationary orientation and position on top of a ball. The stimulus consists of continuous pattern movement in the equatorial zone of the visual field. The rotatory and translatory responses are derived from the signals of a servo-system which maintains the stationary state of the walking fly by appropriate rotations of the ball.
Course control, or the tendency to follow rotatory displacements of the visual surroundings, is established in the wild type and in a behavioural mutant with the eye colour markerw a.The movement detecting systems in the complex eyes on either side respond to the horizontal component of the stimulus and control, predominantly, the thrust of the ipsilateral legs in the wild type, and the thrust of the contralateral legs in the mutant. As a result, front-to-back movement is decreasing the walking speed of the wild type and increasing the walking speed of the mutant, andvice versa.
The course control responses of flying and walking fruitflies depend on the signals of movement detecting systems which are equivalent with respect to the horizontal orientation, the dynamic range, and the resolving power. Leg responses show that the orientation of the movement detecting systems is independent of their position in the eye, and is invariant to the direction and velocity of the stimulus.
The lift control response to the vertical component of the movement stimulus is a quality of the flight system. The response has no counterpart in the optomotor behaviour of the stationarily walking fruitfly.
Functional specialization of the different pairs of legs is not detectable in the present experiments. The rotatory response as well as the translatory propulsion are almost equally accomplished by the fore legs, the middle legs and the hind legs of partially amputated fruitflies.
The optomotor reactions of the fruitfly are accompanied by at least two side-effects of the visual stimulus: The flicker effect acts on the walking speed. The effect is elicited by the temporal sequence of bright and dark stripes in the receptive fields of the visual elements. It is independent of the direction of the pattern movement, and can be produced by a stationarely flickering light source. An after-effect of the pattern movement appears at the end of the visual stimulation. The effect depends on experimental parameters. An initial magnitude of -1/16 of the preceding course control response and a decay time of about 7 min were observed in the present experiments.