Fig. 1. Experimental apparatus to examine sensorimotor interactions in Drosophila. (A) A fly is tethered beneath an infrared diode that casts a shadow of the beating wings onto an optoelectronic wingbeat analyzer (red). The output of the analyzer is coupled with the rotational velocity of the pattern displayed on the wraparound LED screen (green) such that the fly has closed-loop control of the visual panorama. (B) System to deliver a continuous stream of saturated vapor onto the antennae. A computer-controlled solenoid valve shunts a mass-flow-regulated air supply to either a vial of distilled water (experimental control) or a vial of dilute vinegar solution. (C) A pattern of vertical stripes appears to expand from the right and contract to the left of the fly. The velocity of expansion/contraction is in closed-loop such that if the expansion appeared from the right, a turn to the left would reduce the velocity of expansion and vice versa. To examine the strength of visual reflexes, with and without odor, we perturbed the fly's closed-loop control of the expansion/contraction stimulus by adding a 1.25-s bias to the feedback loop (see Materials and methods).