Hi all,
I have a MEG data set which is about 5 minutes long for each subject. I want to detect and correct existing artifacts using the ICA approach using the Brainstorm toolbox. When I performed ICA, the first component (the dominant one) has a very small amplitude, (about 1000 times smaller in comparison to other components) and looks like a DC signal. Should I remove this component? It is the first component and I want to be sure about this decision as it may be a signal, not an artifact. In the following, you can see the components.Thanks!
You should not eliminate unless you can identify a source for the component. See for example https://www.ee.columbia.edu/~dpwe/papers/HyvO99-icatut.pdf, Section 7.1, page 22 in which the authors discuss an MEG experiment in which the test subject was asked to blink and make horizontal saccades, then to bite teeth for as long as 20 seconds. In one version of that experiment, a digital wristwatch was placed in the Faraday cage, and it produced an artifact.
Question: Is the signal very regular, even more that the ECG signal of this paper? If so that is strong evidence that it is an artifact due to an electronic device in the area. Also, it is advisable to conduct such experiments in Faraday cages, since these will filter out nearby artifacts.
The first answer is correct about amplitudes: You cannot determine the amplitude of any component using this method because it normalizes signals.
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