2 fields

add to dataset_description.json the field SimultaneousRecording to indicates the different imaging modalities acquired at the time e.g. SimultaneousRecording: 'func','EEG','eye tracker', 'physio', 'behav'.

add SimultaneousRecordingWith field within the sidecar files to indicates the different imaging modalities acquired at the time and on different hardware.

e.g. ds000117 SimultaneousRecording: {'MEG','EEG'} but no SimultaneousRecordingWith because meg and eeg data are in the same file and recorded together on the same hardware.

SimultaneousRecordingWith

Tibor solution is to point to all files related to each others: for instance in the run-02_bold.json we would have SimultaneousRecordingWith = { 'eeg/sub-01_ses-01_task-something_run-02_eeg.vhdr', 'eyetracker/sub-01_ses-01_task-something_run-02_eyetracker.asc'}.

Chris G proposed to add the relative root path (e.g. {'/sub-01/func/sub-01_task-something_run-02_bold.nii.gz']) to accommodate hyperscanning (simultaneous recordings across participants).

Robert pointed out that 'It might also be relevant to know whether behaviour (behav) was recorded during the functional brain recordings (e.g. func+behav), or prior to (or after) the functional scan. It is often assumed (e.g. in the main bids spec) that these are recorded simultaneously, but e.g. section 8.7 and 8.8 already have to deal with the simultaneous versus sequential (or separate) measurement of the two. When considering SimultaneousRecording as a general field, it might have the side effect of “behav" becoming a mature data type on its own, rather than an addition to functional brain data. This would make it more symmetric'.

Mainak has an open issue: should we split concurrent recordings: eg split the meg and eeg data of ds000117 ; most felt it is not necessary nor recommended since it comes from the same hardware - one issue to solve is then ensure metadata cover all modalities properly e.g. both MEG and EEG without conflict (seems largely possible to me)

synchronization issue

Since we have multiple modalities, each one should have their own timing information recorded using events.tsv files. This is important since different frequency sampling exists for each modality and often clock on different hardware run a different speed. If there is no event (rest) we need at least one marker to ensure this is synchronized (a typical case in point is starting the eeg recording before the MRI starts).

Chris G pointed out that to compare events.tsv they should probably have the same number of rows since there is no unique identifier for events.

future format to be adopted like xdf contains multimodal data (say video screen cap, eye tracker, physio and eeg) with a master clock, and specific clocks -- again splitting files seems redudent and not necessary - but under which folder such file will appear ; my idea would be that's it the experimenter to know / decide and put it under the primary measure of the study.