Baselinecorrection for epoch without baseline period

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#1

Hi everyone,
I’m searching for some input in the following matter:

The study I’m working on is using a paradigm with spoken sentences wich have two signalwords (the triggers). I’m epoching and averaging each trigger seperately so I’m missing a timeperiod to use for baseline correction in front of the second trigger since it is in the middle of a spoken sentence.

I tried using baseline.rescale on the initial raw object with a timeperiod at the beginning of the measurement. It works but is kind of defeating the purpose of a baselinecorrection close to every epoch in a somewhat 30 min measurement with 180 of said sentences.

Is there a method or does someone has an idea for this?

Thank you,
Leoni

#2

I would simply create epochs with a pre-stimulus period that reaches back to the baseline you want to use, then use this baseline period (not the entire pre-stimulus period!) for baseline correction, and then crop the epochs to the time period you actually want to analyze.

1 Like
#3

Thank you very much!
I didn’t realise there is a crop method for epochs.

There is no fixed time between the first and the second trigger, but I think it’s manageable to find a way to set the baseline before the first trigger.

Best wishes,
Leoni

#4

Oh, this is a non-trivial issue then, as MNE expects the baseline period to be the same across epochs, and all epochs must have the same duration.

I may have an idea on how to hack around this, though.

Do you always have both triggers in all of your epochs / trials?

#5

Ah yes, I know. It would be a little bit of an ugly solution, but I just thought I will be able to find a baseline period that works for all trials.

Yes (at least in an ideal scenario). I tried to visualize it :sweat_smile: :

Epochen und Trigger 2
Epochen und Trigger 2810×150 14.7 KB

(The black boxes are the words.)

I’d love to hear your idea!