Fig. 4. Antennal beating field and head orientation shift during curve walking. (A) A representative sequence of head and antennal movements during curve walking. Vertical grid lines mark the three experimental periods (straight, transition, curve). Orientation angles of the head (H) and outer (O) and inner (I) antenna relative to the body axis (see insert for a schematic top view) alternate rhythmically during straight walking. The mean orientation and amplitude of oscillations change after the start of visual motion (line marked with arrowheads). (B) Distribution of antennal orientation angles relative to the body axis over time. Greyscale codes the probability (darker, more probable) of the left (top range) or right (bottom range) antenna to point into a given sector (width 5°). Solid lines indicate mean angles during straight and curve walking, connected by best-fit exponential time course. During straight walking, both antennae are most likely to point at ±33°. After stimulus onset, antennal beating fields shift into turning direction. The shift is faster than for body yaw rotation. (C) As B, but for head angle relative to body axis. Head orientation shifts into turning direction, but slower than antennal beating field. (D) As B, but for antennal angle relative to head. The outer antenna moves closer to the midline but does not cross it. The beating field of the inner antenna shifts into turning direction with a shorter time constant than that of the head.