Extended Data Figure 4: The IT&E algorithm is largely robust to alternative choices of behaviour descriptors.
a, b, The speed of the compensatory behaviour discovered by IT&E for various choices of behaviour descriptors. Performance is plotted after 17 and 150 evaluations in a and b, respectively. Experiments were performed on a simulated, damaged hexapod. The damaged robot has each of its six legs removed in six different damage scenarios. Data are pooled across all six damage conditions. As described in experiment 5 of the Supplementary Information, the evaluated behaviour descriptors characterize the following: (1) time each leg is in contact with the ground (‘Duty factor’); (2) orientation of the robot frame (‘Orientation’); (3) instantaneous velocity of the robot (‘Displacement’); (4) energy expended by the robot in walking (‘Energy (Total)’, ‘Energy (Relative)’); (5) deviation from a straight line (‘Deviation’); (6) ground reaction force on each leg (‘GRF (Total)’, ‘GRF (Relative)’); (7) the angle of each leg when it touches the ground (‘Lower-leg angle (Pitch)’, ‘Lower-leg angle (Roll)’, ‘Lower-leg angle (Yaw)’); and (8) a random selection without replacement from subcomponents of all the available behaviour descriptors (1)–(7) (‘Random’). We created eight independently generated maps for each of 11 intentionally chosen behavioral descriptors (88 in total). We created one independently generated map for each of 20 randomly chosen behavioural descriptors (20 in total). For each of these 108 maps, we performed ten replicates of IT&E for each of the six damage conditions. In total, there were thus 8 × 11 × 10 × 6 = 5,280 experiments for the intentionally chosen behavioural descriptors and 1 × 20 × 10 × 6 = 1,200 experiments for the randomly chosen behavioural descriptors. For the hand-designed reference gait (yellow) and the compensatory gaits found by the default duty factor behaviour descriptor (green), the bold lines represent the medians and the coloured areas extend to the 25th and 75th percentiles of the data. For the other treatments, including the duty factor treatment, black circles represent the median, the edges of the boxes show the 25th and 75th percentiles, the whiskers extend to the most extreme data points that are not considered outliers, and outliers are plotted individually. See experiment 5 in the Supplementary Information for methods and analysis.
