The location effect of a black stripe on the fixation performance of WTB flies.

(A) The MED, which was a contrarian indicator of fixation performance, had a significant location dependence (p = 4.0868×10⁻⁶). The tethered flies showed the best fixation performance when the small black stripe was 20° below them. (B&C) The fixation performance at 2 locations (−20°; 30°) was selected to show more detail. (B) The distribution of the dwelling time in the whole panorama in a 6 min experiment. The distribution of dwelling time had an obvious peak in the central quadrant (−45∼+45° area around the stripe in the panorama) on the location θ = −20°; the distribution of dwelling time was quite even at the location θ = 30°. (C) The distribution of the mean of yaw torque magnitude in the whole panorama. Yaw torque magnitude decreased in the central quadrant and increased in the rest of the area at the location θ = −20°; yaw torque magnitude was more or less the same in the whole panorama at the location θ = 30°. (D) Obvious location dependence in the rDT_abs between the central quadrant and the rest area (p = 2.0731×10⁻⁴). The chart has a truncated y axis for compactness. (E) There was no obvious location dependence in the rDFS between the central quadrant and the rest area (p = 0.1699). These differences were quite small compared to those of torque magnitude. The data in (A–C) are given as the mean±SEM; the data in (D&E) are shown by box plot; the red crosses represent outliers; the p values were calculated by the Kruskal-Wallis test.