Fig. 3.

Modified motor equivalence analysis. In Panel A, data points (A, B, and C) are projected onto the UCM for perfect performance (the hyperbolic curve) computed in normalized units. Both axes are measured in normalized force units (see text). The projected points (Ap, Bp, and Cp) minimize the distances from the respective data points. Segments A-Ap, B-Bp, and C-Cp are the local normals to the hyperbola at Ap, Bp, and Cp, respectively. For data points A and C, the motor equivalent (ME) component is the length of the highlighted portion of the UCM between Ap and Cp. The non-motor-equivalent (nME) component is distance A-Ap minus distance C-Cp, since the points A and C are on the same side of the UCM. Conversely, the nME component for the points A and B is distance A-Ap plus distance B-Bp, since the points A and B are on the opposite sides of the UCM. In Panel B, the ME and nME movements are signed. ME distances are computed from the reference point, and nME distances are computed from the UCM. The bottom figure describes the signs assigned to the ME and nME movements. ME movement is computed from a reference point on the UCM, and nME movement is computed as the orthogonal distance from the UCM for perfect performance