Fig. 3: Walking imitation.

a, Overview of RL set-up. A single policy network is trained to imitate a dataset of 13,000 snippets (around 64 min in total) of freely walking real Drosophila. Full body movements are imitated, including tracking CoM position, body orientation and detailed leg movements. b, Percentiles of errors between the model and the corresponding real fly’s body CoM, and orientation for 3,200 test walking trajectories. c, Filmstrip of the model walking straight at 2 cm s⁻¹ during one full leg cycle, with 8-ms steps between frames. d, Gait diagrams of the fly model tracking synthetic fixed-speed straight-walking trajectories at four speeds. Black stripes indicate the swing phase of leg motion. For each speed, the average number of legs simultaneously in stance position (on the ground) is indicated. e, Number of legs simultaneously in stance position averaged over walking snippet versus average walking speed in snippet. Top, model tracking test set trajectories. Bottom, entire walking dataset. Inset, the distribution of average walking speeds per snippet in the dataset. f, Distributions of swing onset phases of all legs relative to the front left leg L1 in walking trajectories with a mean speed in the range [1.2, 1.7] cm s⁻¹. Blue, fly model tracking test set trajectories; red, entire walking dataset. Dashed lines indicate circular medians. g, Learnt turning strategy. Top, xy projection of leg-tip trajectories in egocentric reference frame for model walking straight (black), turning left (green) and turning right (red), at a constant speed (2 cm s⁻¹). Leg-tip trajectories are shifted horizontally for clarity. Bottom, difference between (egocentric) left and right leg-tip swing length, averaged over all legs, at various walking speeds.