Fig. 4. Difference in stroke amplitude (left-minus-right wing, blue) of Drosophila melanogaster while responding to the black stripe. Time traces show the fly's behaviour 10 s after switching on the stimulus bias. (A–F) Flight at the damping coefficients 52, 156, 260, 520, 1040 and 5200 pNm s, respectively. The outcome of the numerical model for compensation of the velocity bias (Eqn 9) is shown in red. The visual target (black stripe) oscillated with an amplitude of ±48° and 0.5 Hz. The shaded areas indicate fixation behaviour. Positive (negative) differences indicate clockwise (counter clockwise) rotation.