[Dataset][Bug] Zhou2020 S-subjects (1–12) loaded as generic EEG1–EEG41 with no montage

Summary

For Zhou2020, the S-subjects (1–12, 41 EEG channels) are loaded with placeholder channel names EEG1…EEG41 and no montage, whereas the A-subjects (13–20, 26 EEG channels) get real 10–20 names and standard_1005. Any channel-name- or position-based analysis (selecting C3/Cz/C4, sensorimotor ROIs, montage/topographies, Laplacian, etc.) therefore silently fails for 12 of the 20 subjects.

Where

moabb/datasets/zhou2020.py, _get_single_subject_data:

if subject <= 12:
    n_eeg = _S_N_EEG               # 41
    ch_names = [f"EEG{i + 1}" for i in range(n_eeg)]   # <-- generic placeholders
else:
    n_eeg = _A_N_EEG               # 26
    ch_names = list(_26CH_NAMES)   # real 10-20 names

and in _npz_to_raw the montage is only set when names are non-generic:

if ch_names[0] != "EEG1":
    raw.set_montage(make_standard_montage("standard_1005"), on_missing="warn")

So the S-cohort has neither names nor positions.

Impact

12/20 subjects are unusable for any spatial/sensorimotor analysis. Downstream tooling that locates C3/Cz/C4 (or a sensorimotor strip) skips these subjects entirely.

What I checked (the names are genuinely not in the distributed data)

• Raw NPZ (Zenodo record 18988317): the signal array is positional (46 cols = 41 EEG + 4 EOG + 1 trigger); there is no channel-name array.
• NEMAR BIDS mirror (nm000237): sub-01/..._channels.tsv lists EEG1…EEG41 generically and there is no electrodes.tsv. (sub-13, an A-subject, correctly has 26 named channels.)
• Paper (Zhou et al., 2021, Front. Hum. Neurosci. 15:701091): documents only the 26 prior-selected electrodes (== the A-cohort _26CH_NAMES), grouped into SMA/PMC/M1/S1 in Fig 1B. The full 41-channel layout for S-subjects is not given.
• IEEE DataPort / Zenodo description: only "41 EEG + 4 EOG".

Empirical note

I tested the natural guess that the 41 = the 26 selected + 15 extra (i.e. EEG1–26 == _26CH_NAMES, so C3=EEG14, Cz=EEG16, C4=EEG18). A μ-band (8–12 Hz) ERD lateralisation analysis (left- vs right-hand MI) refutes it: EEG14/16/18 are middle-ranked, not the motor channels, whereas an A-subject positive control (real names) shows the expected contralateral C3/C4 pattern. The lateralising channels in the S-cohort sit later in the sequence (≈EEG26–30), consistent with a standard front-to-back acquisition order (e.g. the 64-ch Neuroscan Quik-Cap default), but this cannot be confirmed from the distributed data alone.

Ask

Could the maintainers / data authors provide the ordered 41-channel montage used for the S-subjects (or confirm they follow the Neuroscan 64-ch Quik-Cap default order)? With that, zhou2020.py can set real names + standard_1005 for S-subjects and the whole dataset becomes spatially usable. I'm happy to open the PR once the layout is confirmed.

Start in moabb/datasets/zhou2020.py, especially _get_single_subject_data and _npz_to_raw, and review how S- and A-subject channel metadata is currently handled. The issue is ready to proceed only after the ordered 41-channel S-subject montage is confirmed by the maintainers or data authors; done means that layout is documented well enough to support real channel names and positions.