Visual-Mechanosensory Fusion in Flight Equilibrium The main way that flies maintain stable flight is through sensory feedback from their visual system and their mechanosensory haltere system. The halteres are modifications of the hindwings (recall that dragonflies have four wings, while "true" flies are defined by having only two) into complex sensors that detect Coriolis forces proportional to the angular velocity of the fly. Thus, if a freely flying fly were to be rotated by an external force such as wind, its visual system would be capable of detecting this rotation, but the haltere system would also be stimulated, and is capable of initiating a compensatory response even in the absence of visual feedback. The halteres and visual system act in a complementary fashion, as the rotational frequency bandpass characteristics of each ensure that no matter how slowly or quickly the fly rotates, at least one of these two systems will be sensitive to the rotation (the halteres are most sensitive to fast rotations while the visual system responds better to slower rotations). The Rock-n-Roll arena allows us to quantitatively assess the relative contributions from these two systems to equilibrium flight control. Additionally, studies are currently underway to elucidate the role these two sensory systems play in terminating the rapid turns observed in free flight, called saccades.