Direct Correction of Errors in Position and Speed.

<p>(A) Exemplary plots of how errors in relative position </p><p></p><p></p><p></p><p><mo>(</mo></p><p></p><p><mi>P</mi><mi>n</mi><mo>′</mo></p><mo>=</mo><p><mi>P</mi><mi>n</mi></p><mo>−</mo><p><mi>P</mi><mo>¯</mo></p><p></p><mo>)</mo><p></p><p></p><p></p><p></p> were corrected on each subsequent stride (Δ<i>P</i>_<i>n+1</i> = <i>P</i>_<i>n+1</i> − <i>P</i>_<i>n</i>). Data are shown from 1 trial each for each of the two sub-optimal control model configurations (P_OVC and S_OVC) and for 1 typical human subject. Diagonal lines indicate least-squares fits to each data set. “Perfect” error correction would yield a relationship with a slope of −1 and a strong correlation. (B) Summary results for the slopes of these relationships for all trials for both humans (HU) and for each of the four model configurations (P_MIP, P_OVC, S_MIP, and S_OVC). For the HU data, error bars indicate between-subject ± standard deviations. For the model data, error bars indicate between-trial ± standard deviations. (C) Summary results for the strength of correlation (r²) of these relationships [error bars are defined in the same manner as in part (B)]. While both position control models (P_MIP and P_OVC) exhibited steep slopes (B) with strong correlations (C), both humans and both speed control models (S_MIP and S_OVC) exhibited nearly zero slopes with extremely weak correlations, consistent with <i>not</i> correcting deviations in position. (D) Exemplary plots of how errors in relative speed <p></p><p></p><p></p><p><mo>(</mo></p><p></p><p><mi>S</mi><mi>n</mi><mo>′</mo></p><mo>=</mo><p><mi>S</mi><mi>n</mi></p><mo>−</mo><p><mi>S</mi><mo>¯</mo></p><p></p><mo>)</mo><p></p><p></p><p></p><p></p> were corrected on each subsequent stride (Δ<i>S</i>_<i>n+1</i> = <i>S</i>_<i>n+1</i> − <i>S</i>_<i>n</i>). Data are shown in the same manner as in (A). As in (A), “perfect” error correction would yield a relationship with a slope of −1 and a strong correlation. (E) Summary results for the slopes of these relationships for all trials for both humans (HU) and for each of the four model configurations (P_MIP, P_OVC, S_MIP, and S_OVC) [error bars are defined in the same manner as in part (B)]. (F) Summary results for the strength of correlation (r²) of these relationships [error bars are defined in the same manner as in part (B)]. Human subjects exhibited nearly perfect corrections (i.e., slope ≈ −1: (E)) for errors in speed with strong correlations (F), as did both of the speed control models (S_MIP and S_OVC).<p>