Cannot concat epochs if baseline period was cropped off

[hoechenberger]

Description of the problem

concatenate_epochs() refuses to operate on Epochs if their baseline period has been cropped away.

Steps to reproduce

# %%
import mne

sample_dir = mne.datasets.sample.data_path()
sample_fname = sample_dir / "MEG" / "sample" / "sample_audvis_raw.fif"

raw = mne.io.read_raw_fif(sample_fname)
raw.crop(tmax=60)

events = mne.find_events(raw, stim_channel="STI 014")
event_id = {
    "auditory/left": 1,
    "auditory/right": 2,
    "visual/left": 3,
    "visual/right": 4,
    "face": 5,
    "buttonpress": 32,
}

epochs = mne.Epochs(
    raw,
    events=events,
    event_id=event_id,
    tmin=-0.2,
    tmax=0.5,
    baseline=(None, 0),
    preload=True,
)

epochs.crop(0, None)  # crop away baseline period
mne.concatenate_epochs([epochs, epochs])

Link to data

No response

Expected results

Concatenation should work

Actual results

ValueError: Baseline interval [-0.19979521315838786, 0.0] s is outside of epochs data [0.0, 0.49948803289596966] s. Epochs were probably cropped.

Additional information

–

[agramfort]

why cropping the baseline in the first place?

…

Message ID: ***@***.***>

[hoechenberger]

why cropping the baseline in the first place?

It's something we do in MNE-BIDS-Pipeline during decoding, which we usually start at time point zero (as to omit the baseline). We crop the epochs and then concatenate epochs of different conditions before feeding them to the classifier.

I have now simply changed the order of doing things: first concat, then crop.

It's a viable workaround, but I believe not being able to concat if the baseline has been cropped is unintended behavior, hence a bug

Nothing urgent, but I think we should fix it if / when we have time

The problem started showing up while working on mne-tools/mne-bids-pipeline#796