[Eeglablist] Question about sorting epochs

[Arnaud Delorme]

> Hi Arno,
> 
> Thanks for the reply! About the second part of your answer, the problem is that these stimuli are applied in series (to induce an illusion), so the baseline of each of those epochs is contaminated by the stimulus applied before. Therefore, I want to use those 2 seconds of wait at the beginning of the trial as the baseline for each stimulus event. Each trial has 2 seconds of no stimulus, then a series of 5 stimuli. Epoched, it would be one segment of 2 s and five segments of 1 s each (the stimulus' of the event is at time zero there). Then copy the 2-s-long segment and paste it at the beginning of each stimulus segment, so we end up with five 3-s-long epochs. I wonder if anyone has a script for this.

There is sometimes drift in EEG signals so I think high pass filtering at 0.5 Hz would be better than applying a baseline. But if you want to apply a baseline, you can extract 10 second epochs containing all of your stimuli and apply the 2 second baseline, then extract smaller epochs from these large epochs for each type of stimuli (then create a study to compare them).

Cheers,

Arno

> Best,
> Renzo
> --
> 
> 
> 
> 
> 
> On Tue, 4 Apr 2023 at 07:59, Arnaud Delorme via eeglablist <eeglablist at sccn.ucsd.edu> wrote:
> > I was wondering if you could help me with something. I have EEG datasets
> > that need an unconventional treatment before analysis. In this experiment,
> > participants hear a beep (event 1), and 2 seconds later, a series of 5
> > stimuli are shown, with 1 second of separation in between (events from 2 to
> > 6). After pre-processing and epoching, epochs with event label 1 are 2000
> > ms long (from 0 to 2000 ms, no stimulus) and the other epochs are 1000 ms
> > long (from -500 to +500 ms, where time zero indicates stimulus
> > presentation).
> > 
> > How can I average across all the epochs with event label 1, 2, 3, 4, 5, and
> > 6
> 
> This is best done by creating an EEGLAB study (which can be created with 1 participant only).
> Then you can compare epochs 1, 2, 3, 4, 5 and 6.
> 
> > and then copy the epochs with event label 1 to every other epoch so the
> > resulting epochs are 2000 ms (duration of epoch 1) + 1000 ms (duration of
> > each stimulus epoch)? Thus, we’d have resulting epochs of -2000 ms to +1000
> > ms. The objective is to use the epoch with event number 1 as baseline for
> > the stimulus-related epochs (event numbers 2, 3, 4, 5, and 6).
> 
> This would require a script. 
> It is unclear what you are trying to do. If it is a standard ERP baseline, you can extract very long epochs with events 1, 2, 3, 4, 5, and 6 compute the baseline, then extract smaller epochs.
> 
> Cheers,
> 
> Arno
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