Fig. 6. Saccadic flight style of Drosophila flying freely in a non-rotating random-dot arena. (A–C) Three flight paths of single fruit flies voluntarily starting from rest (top view). Flight is characterized by sequences of straight flight interspaced by 130 ms short, approximately 90–180° saccadic turns. Horizontal forward velocity is plotted in pseudo-colour. Red cross, arena centre. (D) Angular velocity during flight saccades elicited at various forward velocities in response to optomotor stimulation. Each data point of a curve represents the averaged value derived from the mean saccadic velocity of each of the 131 tested fruit flies. The mean standard deviations over all data points of each curve amount to 546 (black), 425 (red), 347 (green), 263 (blue), 287 (cyan) and 513° s^–1 (purple). (E) Modulation in horizontal velocity during flight saccades. The standard deviations averaged over all data points of a curve amount to 0.12 (black), 0.12 (red), 0.15 (green), 0.10 (blue), 0.13 (cyan) and 0.17 m s^–1 (purple). (F) Frequency of saccades slightly increases with increasing horizontal velocity estimated from flight sequences between saccades (intersaccade velocity). The black line represents the linear regression fit on the data set (y=1.31x+2.55, R²=0.04, N=131 saccades, P=0.024). Colour coding in D–F: 0° s^–1, 0.26±0.08 m s^–1, 22 (black); 100° s^–1, 0.27±0.08 m s^–1, 23 (red); 300° s^–1, 0.33±0.07 m s^–1, 20 (green); 500° s^–1, 0.45±0.06 m s^–1, 20 (blue); 700° s^–1, 0.49±0.09 m s^–1, 21 (cyan); and 900° s^–1, 0.45±0.09 m s^–1, 26 (purple); for arena velocity, mean forward flight velocity and number of flies, respectively.