Figure 1. Open loop experiments for measuring a Drosophila's orienting behavior (torque responses) to competing stimuli.

(A) Schematic drawing of the flight simulator system. Two identical paper strips, having the same black and white stripe pattern, curve along the surface of a transparent cylinder on the left (red) and right (blue) of a tethered flying fly, thus forming the left and right scenes, respectively. The scenes are moved by an electrical motor. The yaw torque of the fly, i.e. its responses toward the moving scenes, is measured by an opto-mechanical torque meter. A small mirror linearly reflects changes in the yaw torque; the light-return of a laser beam over distance greatly amplifies this signal for an optical sensor. (B) Because the fly's head is clamped in a fixed position and orientation, preventing its movements, the fly should see two identical scenes, on its left and right, which simultaneously move to the opposite directions without any overlapping visual fields. Thus, this stimulation generates two isolated monocular flow fields, one for each eye. The fly's torque response indicates which of the two stimuli (moving scenes) it has chosen to pursue at any one time.