Fig. 1. (A) The mechanosensory haltere is a small club shaped modified hind wing. (B) Oblique view and (C) side, top and end views of the apparatus for delivering visual and mechanosensory stimuli. A wrap-around light-emitting diode (LED) display is mounted within a 3-degree-of-freedom rotational gimbal. The fly is mounted in the center of the visual display, above a sensor that measures the left and right wingbeat amplitudes. (D) Visual patterns are used to simulate optic flow generated when the fly rotates around the roll, pitch and yaw axes.