Optimizing Complexity Measures for fMRI Data: Algorithm, Artifact, and Sensitivity
Figure 2
Number of spikes (as a percentage of points in a time series, x-axis) and their magnitude (in units of standard deviation of original time series, y-axis) affect Hurst estimates differently.
The z-axis represents normalized to [0, 1] range one-sample t-test differences from the H-estimates of time series without spikes (each point on the surface is the t-value difference in H resulting from the introduction of spikes to the time series; the set of all t-scores for all measures was linearly transformed to [0, 1] range to show relative change due to presence of spikes). Volume is calculated as the difference between the surface and the plane defined by H-values of unaltered time series (spike magnitude of zero).