Comparison of the 2D projections of the first component of the PCA of perceptual data and the first component of the PCA of the three arm dynamics parameters.
Each subplot shows a projection onto a slightly different plane, as the plane is determined by the mean vector of the perceptual data and the mean vector of the arm dynamics parameter of interest. Each line shows the orientation of the first component of the PCA of the data of one participant. All vectors are unit vectors. The light gray shapes show the projection of shoulders, upper and lower arm of a participant in the experimental posture. (a) Perception (black) and stiffness (pink) vectors. (b) Perception (black) and damping (green) vectors. (c) Perception (black) and inertia (blue) vectors. (d) Projected angle of each of the data sets shown in panel a–c, with respect to the light blue axis (which is defined by the mean of the perceptual data set, which is obviously 0 in this definition). Note that none of the arm dynamics parameters are oriented perpendicular or parallel (i.e. 90 or 0°) to the perceptual data.