Distributions of intersaccadic azimuthal feature positions reveal that maneuvering birds stabilize arena features in their frontal visual field.

<p>(A) Schematic top view into the arena. Azimuthal positions of wall corners, the gray square and the perch (colored lines) were obtained relative to the bird’s head yaw orientation (red line). (B) Relative azimuthal angles of arena features for the example flight shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129287#pone.0129287.g002" target="_blank">Fig 2</a>. The thick green line depicts the angle of the perch center. The gray shaded area represents feasible horizontal eye motions of ±10° relative to the horizontal head orientation. Positive azimuthal angles represent the left visual hemisphere, negative values the right visual hemisphere (see bird illustration above legend). Note that the diverging azimuthal angles of the perch edges (dark green and blue lines) are caused by the bird getting closer to the perch. Approaching the perch causes the retinal size of the perch to expand in the bird’s frontal visual field. (C-F) Averaged relative azimuthal distributions of arena features that were stabilized in the frontal visual field in the intersaccadic phases during a turning on a dime maneuver; before the turn (C: fine dashed line), during the turn (D & E: solid line) and after turning (F: coarse dashed line). Averaged distributions illustrate left turn flights (<i>n</i> = 92, <i>N</i> = 5). Standard deviations across birds are illustrated by the colored areas. (G-K) Intersaccadic azimuthal distributions for arena features that were not stabilized in the frontal visual field. By stabilizing the perch center frontally after the turn (F), the right and left edge distributions are positioned more laterally, are broader and have lower peaks than the center (E & K). The vertical bar extending ±10° illustrates feasible horizontal eye motions relative to the head orientation in unrestricted birds (review: [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129287#pone.0129287.ref014" target="_blank">14</a>]). Perch position for 92 flights is approximated by using the position of a static perch (thick lines in panel E-F, <i>n</i> = 92 flights, <i>N</i> = 5). For 15 left-turn-flights tracked at 2000 Hz, the position of the swinging perch relative to the birds was tracked as well (gray dashed line in panel E, F & K <i>n</i> = 15 flights, <i>N</i> = 5). For normalization, we divided each distribution by the cumulative sum of all other feature distributions. Binning = -90:10:90.