An essential step in uncontrolled manifold analysis is creating a linear model that relates changes in elemental variables to changes in performance variables. Such linear models are usually created by means of an analytical method. However, a multiple regression analysis is also suggested. Whereas the analytical method includes only averages of joint angles, the regression method uses the distribution of all joint angles. We examined whether the latter model is more suitable to describe manual reaching movements. The relation between estimated and measured fingertip-position deviations from the mean of individual trials, the relation between fingertip variability and nongoal-equivalent variability, goal-equivalent variability, and nongoal-equivalent variability indicated that the linear model created with the regression method gives a more accurate description of the reaching data. Therefore, we suggest the usage of the regression method to create the linear model for uncontrolled manifold analysis in tasks that require the approximation of the linear model.
Inge Tuitert, Tim A. Valk, Egbert Otten, Laura Golenia and Raoul M. Bongers
Melanie Krüger, Thomas Eggert and Andreas Straube
Empirical evidence suggests that the ability to stabilize important task variables of everyday movements by synergistically coordinating redundant degrees of freedom decreases with aging. The aim of the current study was to investigate whether this decrease may be regarded as a characteristic that also applies for the control of multiple task variables. We asked younger and older subjects to repeatedly reach towards and grasp a handle, while joint angle movement of the arm was recorded. The handle constrained final hand position and final hand orientation. Movement variability was analyzed during movement execution by using the uncontrolled manifold method. Results showed that hand orientation was less stabilized in younger than in older subjects. We conclude that aging changes the stability of important task variables. These changes may lead to decreased stability in some task variables, as reported in the literature, but also to increased stability in other task variables.