Fly Turning Behavior Measurement

The fly’s turning behavior was measured with the fly-on-a-ball rig, as described in previous studies (Clark et al., 2011 (link); Creamer et al., 2018 (link)). The fly was tethered above a ball floating on a cushion of air. The ball served as a treadmill such that the fly could walk and turn while its position and orientation were fixed. The rotational response of the fly was the averaged rotation magnitude of the ball in 1/60s bins with an angular resolution of ~0.5°. Panoramic screens surrounded the fly, covering 270° horizontally and 106° vertically (Creamer et al., 2019 (link)). A Lightcrafter DLP (Texas Instruments, USA) projected visual stimulus to the screens with chrome green light (peak 520 nm and mean intensity of 100 cd/m²). The spatial resolution of the projector was around 0.3° and the projector image was updated at 180 Hz. The rig’s temperature was 34-36°.