What does "sample" pertain to in events.tsv?

As of version 1.6.0, the description for the sample column name in the events.tsv file is: “Onset of the event according to the sampling scheme of the recorded modality (that is, referring to the raw data file that the events.tsv file accompanies).

This is a bit unclear to us, and were wondering what this pertains to? Additionally, should the units for this field be in seconds (just like onset)?

The unit seems to be in “samples” (1 / sampling rate). For example, in BOLD, the sample is the volume, so you would indicate the first sample with 1 (or possibly 0, depending on the outcome of https://github.com/bids-standard/bids-specification/issues/499).

Edit: As to why this exists, I think it’s more common in M/EEG. Perhaps it is sometimes more useful to identify an event as occurring during a sample rather than at a time offset that needs to be multiplied by the sampling rate and rounded to an integer. We could probably do a bit of digging to find what version it was introduced in.

1 Like

Ah okay. I could see how it likely applied to non-MRI modalities, but thanks for your explanation.

@effigies is correct, sample was introduced in the EEG and iEEG BEPs, if I remember correctly.