Fig. 8. Flight orientation was quantified in response to competing wind and visual stimuli. Flies were presented with 39 different combinations of wind velocity, expansion rate and orientation of the expansion pattern. (A) Exemplar responses are shown to a striped pattern expanding at a temporal frequency of 1.0·Hz, from a focus of expansion (FOE) at ±90°, in the absence and presence of a 0.6 m s^–1 wind [location of the focus of contraction (FOC) is indicated by the red bar, orientation favored by wind is indicated by the blue bar]. (B) To quantify the preference for the visual or wind stimulus, the number of instantaneous heading vectors in each trial that fell within ±45° of 0° (blue shaded area) was divided by the total number falling within ±45° of 0° and ±45° of the FOC (red shaded area). This yielded a preference index between 1 (wind preferred) and 0 (FOC preferred). In B, the arrows represent the mean orientation vectors of each fly in A over the full 5 s trial.