Fig. 4. (A) Probability density function at the intersaccadic intervals of head yaw (blue), body yaw (red) and tuned body yaw (green) velocity. (B–D) Power spectra of sideward (solid) and yaw (broken) angular velocity for body yaw velocity (B), head yaw velocity (C) and tuned body yaw velocity (D); power spectral densities were calculated for the intersaccadic intervals using an algorithm by (Scargle, 1989; see also Kern et al., 2005b). Sideward is perpendicular to the head's plane of symmetry. Since the optic flow resulting from translational movements depends on the distance to environmental objects, sideward velocities of the fly were converted to angular velocities by multiplying by the nearness (equal to the inverse of the distance) (Koenderink, 1986) averaged over the trajectories and over the receptive fields of the neuron (average nearness: 7.14 m^–1, corresponding to a typical distance to the arena wall of 0.14 m). Data based on two flights originating from different flies. Note that the y-axis in B is scaled differently from those in C and D.