Fig. 5. The effects of expansion rate on collision-avoidance and landing responses. Each column represents the wing-beat amplitude (WBA), and the landing response probabilities plotted against stimulus position as described in Fig. 4 for a different rate of expansion. The functions shown in Fig. 4 were determined for each fly, with each data point representing the mean ± S.E.M. taken over all the flies. The numbers of flies tested were 8, 11, 11, 8, 12, 11, 8, 10, 7, 7 and 5 for expansion rate in ascending order (starting at 100° s^-1). The total numbers of stimulus presentations, again in ascending order, were 1945, 2905, 2584, 1746, 3237, 2529, 216, 2223, 1771, 1391 and 1132. The sinusoidal shape of the wing-stroke amplitude responses holds for all expansion rates, with the amplitude of the response being largest for an expansion rate of 1000° s^-1. The probability of landing is high over the greatest range of positions at an expansion rate of 1430° s^-1. L, left; R, right; WBF, wing-beat frequency.

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