Cross-validation and sensitivity.

To combine reconstruction performance into a single error metric we normalized the RMS of the error for each decile (averaged across animals) to the RMSE of the two feature reconstruction (*** indicates P<0.001 for all paired conditions). In addition to the standard reconstruction (A) we repeated the feature extraction and model testing with Δt included in the original U matrix (B) and with the phase-triggered rather than spike-triggered torque waveforms (C). Finally, we cross-validated (D) the reconstructions performing 1000 replicates with 70% of the wingstrokes as a training set and 30% withheld for a test set. Model abbreviations: 2F—two features, S_Δt—differential synergy, S_PC—empirical (PCA) synergy, R—redundancy, I—independence, S_{< τ >} mean torque differential synergy, I_{< τ >}—mean torque independence.