How projectors are handled in channel file when importing data from raw

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#1

Hi,

I have a raw file for review. I'm using projectors to correct artifacts (e.g. blinks). When I'm satisfied at first (say for condition 1), I choose a bunch of SSPs to remove and import my data time locked to events of condition 1. The channel file (containing SSP projectors) gets copied to a new folder. (correct?).

After a while, I go back to my raw data to process condition 2 and choose a different SSP (or even a different method, say ICA or even no projector at all) to correct my artifacts. Import these new trials again. What happens to the channel file? does it include previous and/or new projectors?

My understanding is that only the first set of projectors is stored in the channel.mat. Is that not a problem?

I admit this is a borderline use case, and I suppose the correct thing to do would be to rename the formerly imported folder before importing again, so as to create a new channel file in a different folder (I just tested that, and I get the expected result). But is this not a potential source of error (a difficult one to catch)?
Or perhaps I don't understand something in the way projectors are stored and/or applied at import...
Otherwise, I suppose it would be important for provenance tracking and consistency in the channel.mat file to at least issue a warning or error message, and at best import under a different study folder.

This is obviously not just a thought experiment (though I simplified the situation here for clarity), but an actual use case I've been facing recently.

Thanks a lot for any comment.

#2

This is in fact, not common scenario, as usually the Projectors are applied for the entire raw file, and conditions are imported at the same time (thus using the same projectors). But nevertheless it is interesting. Here some so comments:

Yes, if it is done as described: importing different Conditions with different Projectors to the same folder.

At importing Condition_1 events, the Projectors_1 are applied on the data, this is imported and the
the raw channel file is copied to the folder as ChannelFile_1. After, when Condition_2 events are imported (using different Projectors), the Projectors_2 are applied on the data, this is imported to the same folder, but ChannelFile_1 stays unchanged.

To avoid this situation (with one raw file), at importing Condition_1 and Condition_2, if they have different Projectors, the option Create a separate folder for each event type should be selected: two folders, two channel files, two different sets of projectors. Note that the case of importing more than one raw file using the separate folders may cause the same issue see the last comment below.

When importing a raw file the projectors are applied on the data, then the "cleaned" data is imported to the database. This is why the option Select active projectors is not available in the imported.

The imported channel file is a copy of the raw channel file plus an entry in the History field that indicates the imported channel is indeed imported from raw.

Indeed, as mentioned above, the information on the Projectors_2 will not be saved, although they will be applied at importing the data.

A message suggesting to create a separate folder (or rename the already imported folder) would be a good idea if folder-to-import-to exists and its channel file differs from the raw channel file. This will also help in the strange scenario of importing the same condition from two or more raw files to the same Condition folder.

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