"Epoching" TF maps

Discussions
1

Hi,

I need to compute TF on long epochs (according to a certain marker) and then re-epoch (according to another marker, within the epoch). This is because for each trial I have an auditory stimulus of different duration, and I need 300 ms before that stimulus onset for baseline correction, but then the window of interest is based on the offset of that variable stimulus.

So the idea is to compute individual TF maps based on stimulus onset marker, correct for baseline (ERS/ERD), then cut the maps according to the offset marker (which is included in the original epoch), and then average the TF maps.

Is there a way to do so?

Thanks,
Simone

2

Hi Simone,

The “Import MEG/EEG” interactive menu and process are not designed to work on time-frequency files.
The only solution to cut your time-frequency maps is to define manually the time window of interest, and extract it with the processes “Extract > Extract time” or “Extract > Extract values”.

Francois

3

Hi,

Thanks for the reply. Elsewhere I got the following suggestion for solving this problem: having two epochs for each trial, one around the baseline (epoch 1) and one around the time-window of interest (epoch 2), and then compute the TF on epoch 2 taking the baseline from epoch 1 with “Process 2”. Do you agree?

Thanks,
Simone

4

Yes, you can use two different files. The baseline and epoch to normalize do not have to be in the file.

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