How to choose a noisy time series for participants to obtain EEG signals in a natural viewing scenario, with one viewing as one EEG recording? If I am interested in the positive and negative emotions induced by natural viewing, can I use EEG with neutral emotions as a noise sequence? If possible, how to obtain the average noise covariance matrix of a subject (the sequence length recorded in each EEG is different)?
Hello Scarlet,
maybe this thread will help you decide on the time window to use for covariance estimation https://mne.discourse.group/t/meg-source-reconstruction-and-sensor-topography-dont-agree/8853/5
Best,
Carina
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Intuitively I would say no. I’d process these 3 conditions separately, and eventually look at the contrasts positive – neutral, negative – neutral, and positive – negative. But I’m no expert in this field.
If you don’t have anything that could serve as a pre-stimulus baseline period, you may consider creating an ad-hoc covariance matrix instead.
Best wishes,
Richard
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Thank you for providing the link. I understand how to choose time windows to calculate the covariance matrix! 
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Thank you for your suggestion. I have found the pre stimulus baseline period in the my data.
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