Fig. 2. Schematic of experimental setup. A computer generated stimulus was projected into a white cylinder, at the center of which an insect was mounted. Behavioral responses were recorded with a video camera for frame-by-frame analysis (inset). The animal's head deflection was measured as the angle between a line through the centers of both eyes [transverse axis of the head (c) and the transverse axis of the body (b)]. Longitudinal body axis (a) was used to determine the transverse axis of the body (b).