Handling EXG1 and EXG 2 channels for montage in EEG Biosemi 64

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Hi! I’m new to MNE and EEG processing.

I’ve run some experiments with a Biosemi ActiveTwo with 64 channels and used some external channels (EXG1 and EXG2) in mastoids in order to re-reference the signal prior to the data cleaning and analysis process.

However, when setting the montaje with raw.set_montage(“biosemi64”), I got:

ValueError: DigMontage is only a subset of info. There are 2 channel positions not present in the DigMontage. The channels missing from the montage are: [‘EXG1’, ‘EXG2’].

I could solve it by setting the channel type to eog or misc. But maybe there is a more straighforward way or maybe I’m missing something with the montage.

Thanks

Fede

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Setting the channel types to eog or misc is usually what I do too. Alternatively you could try

  • raw.set_montage("biosemi64", on_missing="ignore") (although this could cause you some trouble down the line .i.e when plotting topomaps).

  • dropping the channels before setting the montage (if you won’t need them).

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Thanks Scott! I think all three approaches migth be ok but setting the references as misc may be more elegant

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