Fig. 1. Experimental apparatus and flight path analysis. (A) Flight arena for measuring free-flight performance in Drosophila under optomotor stimulus conditions. A gear motor rotates the visual environment at distinct angular velocities, and three circular fluorescent light tubes (FLT) illuminate the visual pattern from behind. The flies are automatically released into the arena bottom (outlet) via a microprocessor-controlled gate. A high-speed video camera is triggered when the animal takes off, and cardboard shields the experimental setup from ambient light. (B) Estimation of flight altitude. Pictograms show typical video images of unrestrained animals flying at various altitudes. The red borderline outlines the fly body (oval blob), the inner dot indicates the centre of mass, and the line shows body orientation. Plotted data are derived from a tethered fly that is vertically moved by hand inside the middle of the arena. Red line shows linear regression fit. Means ± s.d.; N=10 flies. (C) Random dot pattern used in the experiments. (D) The fly's gaze (β) is defined as the angle between 0° direction and a line running through the arena centre and the point of path convergence projected on the outer pattern cylinder. (E) Angular velocity of the animal is calculated from the temporal change in angular orientation (d/dt) given by three successive data points within the x/y coordinate system. r, path radius; t, time.