Object detection in the fly during simulated translatory flight

Abstract

Translatory movement of an animal in its environment induces optic¯ow that contains information about the three-dimensional layout of the surroundings: as a rule, images of objects that are closer to the animal move faster across the retina than those of more distant objects. Such relative motion cues are used by¯ies to detect objects in front of a structured background. We confronted¯ying¯ies, tethered to a torque meter, with front-to-back motion of patterns displayed on two CRT screens, thereby simulating translatory motion of the background as experienced by an animal during straight¯ight. The torque meter measured the instantaneous turning responses of the¯y around its vertical body axis. During short time intervals, object motion was superimposed on background pattern motion. The average turning response towards such an object depends on both object and background velocity in a characteristic way: (1) in order to elicit signi®cant responses object motion has to be faster than background motion; (2) background motion within a certain range of velocities improves object detection. These properties can be interpreted as adaptations to situations as they occur in natural free¯ight. We con®rmed that the measured responses were mediated mainly by a control system specialized for the detection of objects rather than by the compensatory optomotor system responsible for course stabilization.

Detection of object motion by a fly neuron during simulated flight

“…The same stimuli were used as in previous behavioural experiments (Kimmerle et al 1997). The stimuli were presented on two CRT screens (Tektronix 608; see Fig.…”

“…The stimuli were presented on two CRT screens (Tektronix 608; see Fig. 1A in Kimmerle et al 1997). The CRT screens were placed symmetrically in front of the¯y subtending an angle of 90°.…”

“…In a behavioural study with ā ight simulator it has been shown that tethered¯ying ¯ies, under certain conditions, try to turn towards an object which was presented during simulated translatorȳ ight (Kimmerle et al 1997). Translatory motion was mimicked in these experiments by front-to-back motion of gratings displayed in front of the¯ies' eyes.…”

“…The present study analyses to what degree FD-cells can account for the object-directed turning behaviour elicited during translatory¯ight (Kimmerle et al 1997). The analysis is done on a representative of the FD-cells.…”

“…The FD1b-cell is ®rst characterised shortly. Its responses to relative motion are then compared to the behavioural responses which were previously elicited by the same stimuli (Kimmerle et al 1997). On the basis of this comparison further processing steps in the sensory-motor pathway of the object detection system of the¯y are discussed.…”