a, Side view of a fly walking on an air-cushioned ball during an electrophysiology experiment. b, Image of the ball and plastic holder. Air flows up through the holder and out the semi-spherical depression that cradles the ball. c, Schematic of the experimental set-up viewed from above. The fly is secured in an aperture in the centre of a horizontal platform. The platform is surrounded by a circular panorama. The panorama is composed of square LED arrays49 (2 squares vertically × 12 squares horizontally). The ball is illuminated by an infrared (IR) LED, which is visible as a red spot in b. A camera captures an image of the ball to enable tracking using FicTrac48. Inset shows FicTrac view. Camera and infrared LED are not drawn to scale. d, The yaw velocity of the fly compared to the cue position. This is the dataset that is the basis for Fig. 1f, but here broken down into averages for each individual fly, and with right (+) and left (−) cue positions kept separate. Positive velocities are right turns, and negative velocities are left turns. No tests showed a statistically significant yaw velocity (P < 0.05, two-sided comparison to bootstrap distribution) for any individual fly at any cue position. For details of analysis, see Methods, ‘Yaw during open-loop epochs’. e, Yaw velocity in response to the visual cue presentation. This analysis is the same as that shown in Fig. 1f, but here yaw velocity is plotted against the distance of the cue jump between consecutive trials. As in Fig. 1f, we show mean (black) ± 1 s.d. (grey) across experiments (73 experiments in 68 flies). Magenta lines show the bootstrapped 95% confidence interval of the mean across flies after randomizing cue positions, Bonferroni-corrected for multiple comparisons. Because the mean lies within these bounds, it is not significantly different from random. This analysis further supports the conclusion that there is no systematic yaw response to the random flashes of the vertical bar. For details of analysis, see Methods, ‘Yaw during open-loop epochs’. f. The visual receptive field of an example cell measured multiple times over the course of a 40-min recording. Each row shows data from a separate visual mapping epoch. Data from this example cell are also shown in Fig. 1e. Note the stability of the visual receptive field over this time period. For experiments shown in this figure, we used UAS-mCD8::GFP/UAS-mCD8::GFP; R60D05-Gal4/R60D05-Gal4 flies.