Fig.5.

Examples of recovered mean HRFs for four selected subjects, channels and tasks for every technique for both HbO (solid line) and HbR (dashed line). HbR HRFs have been shifted in baseline towards negative values for visualization purposes only. In a) Wavelet, and CBSI provide some minimization of the motion artifact, while PCA_80 increases it. In b) all techniques but PCA_97 are able to recover physiological HRFs, no motion correction included; PCA_97 highly underestimates the HRF. c) is an example of PCA_80 and PCA_97 adding a motion artifact in a motion-free channel and d) is an example of a channel in one subject where the Kalman filter is unstable. Gray line represents the actual task duration, 850 ms, which is the grand average of the reaction times, i.e. the time needed by participants between the appearance of the word and the color being pronounced.