Fig. 6. In closed-loop conditions, flies show a powerful steady-state expansion avoidance reflex. By adjusting the difference between the right and left wing stroke amplitude, flies control the azimuth of (A) a random checkerboard pattern (N=27), (B) a single vertical stripe (N=27) and (C) the poles of a constantly expanding/contracting pattern of vertical stripes (N=13). For each experimental treatment, example responses are plotted in the left column (i), time series averages are plotted in the center column (ii; indicated in grayscale) and total probability distributions are plotted in the right column (iii). For the grayscale plots, the white area indicates that flies maintained the rotating pattern in that particular position. On average, flies do not show preference for any single element of the random checkerboard pattern, whereas they tend to fixate the vertical stripe in front (0°). Flies show even more robust fixation of the poles of expansion/contraction. There is less variability in the fly's tendency to stabilize the poles of the expanding pattern in the rear field of view, thus the pole of contraction is fixed frontally.