TY - JOUR
T1 - Distributional properties and variance-stabilizing transformations for measures of uncontrolled manifold effects
AU - Verrel, Julius
PY - 2010/8
Y1 - 2010/8
N2 - In the uncontrolled manifold (UCM) approach, variability in elemental variables (such as joint angles or muscle modes) is decomposed into goal-equivalent and non-goal-equivalent variability components (GEV, NGEV) with regard to a specified task variable. A UCM effect is present, when GEV exceeds NGEV, and different indices have been proposed to quantify the strength of UCM effects. We propose variance-stabilizing transformations for each of these measures. Our results indicate that the variability components should be log-transformed prior to statistical analysis, to reduce non-normality and inhomogeneity of variances. Moreover, it is formally shown that the UCM indices are identical after appropriate variance-stabilizing transformations. The theoretical analysis is illustrated by empirical and simulated data from a study on manual pointing.
AB - In the uncontrolled manifold (UCM) approach, variability in elemental variables (such as joint angles or muscle modes) is decomposed into goal-equivalent and non-goal-equivalent variability components (GEV, NGEV) with regard to a specified task variable. A UCM effect is present, when GEV exceeds NGEV, and different indices have been proposed to quantify the strength of UCM effects. We propose variance-stabilizing transformations for each of these measures. Our results indicate that the variability components should be log-transformed prior to statistical analysis, to reduce non-normality and inhomogeneity of variances. Moreover, it is formally shown that the UCM indices are identical after appropriate variance-stabilizing transformations. The theoretical analysis is illustrated by empirical and simulated data from a study on manual pointing.
UR - http://www.scopus.com/inward/record.url?scp=77955773298&partnerID=8YFLogxK
U2 - 10.1016/j.jneumeth.2010.06.016
DO - 10.1016/j.jneumeth.2010.06.016
M3 - Journal articles
C2 - 20599556
AN - SCOPUS:77955773298
SN - 0165-0270
VL - 191
SP - 166
EP - 170
JO - Journal of Neuroscience Methods
JF - Journal of Neuroscience Methods
IS - 2
ER -