Questions about Epochs

Hi,

I am trying to apply an apply ICA on my EEG data. In order to upload my
data (of which the format in not available in mne package) I used
EpochsArrray, by creating a 3d array with the suggested shape (n_epochs,
n_channels, n_times).

But after the creation of epochs, I noticed that the microvolts of my
original data change after creating epochs (by running EpochsArray). Here
below an example:

*Script:*
# 3d array created by me with shape: n_epochs, n_channels, n_times

print "data point from my array", 3dArray[0][0][0]
# here I want to print a data point from my 3d array

montage=mne.channels.read_montage('easycap-M1')
info = mne.create_info(channel_names,500,ch_types=channel_types,
montage=montage)
picks = mne.pick_types(info, meg=False, eeg=True, misc=False)

# I create my epochs
epochs= mne.EpochsArray(3dArray, info=info, tmin=0,baseline = (0, 0.04))

print "data point from the created epochs", epochs.get_data()[0][0][0]
# here I want to print a data point from the created epochs

*Output:*

data point from my array 55.592026
data point from the created epochs -1.37142819048

Is that normal? I strongly fear I am missing some steps.

Many thanks,
Emanuela Liaci
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Hi Emanuela,

in this line:

epochs= mne.EpochsArray(3dArray, info=info, tmin=0,baseline = (0, 0.04))

you apply a baseline (0, 0.04) to the data. This could be it. Specifying the baseline parameter does not mean that you annotate the data that this baseline has been applied, it actually applies one.

regards,
Marijn.