Crosschecking
This is step 1: before your data can be processed, your raw recordings need to be converted into the standard folder layout analysis expects (called "BIDS") and crosschecked. This page explains what that means and why it matters — it applies whether your data is from FOH, Crane, or both. Once you've read this, go to FOH Crosscheck or Crane Crosscheck for the tool-specific walkthrough. You may use one or the other, or both, depending on which experiment(s) your data comes from — neither tool depends on the other.
What is "crosschecking"?
When a raw recording session gets converted into BIDS, the conversion step doesn't try to be clever about picking files. If a session was restarted, a filename is ambiguous, or there are two recordings that could both plausibly be "the real one," the converter just keeps all of them rather than guessing. That's deliberate — guessing wrong and silently keeping the wrong file would be far worse than leaving the decision to a person.
Crosschecking is that person's job: going through each subject's folder and confirming — or fixing — which file is the right one, so everything downstream can trust it without re-checking. It's a filing and bookkeeping step, not a data-quality step (more on that distinction below). Critically, it is a bookkeeping step in a very literal sense: the point of these tools is never to change your raw data — it's to build up a written record of every decision made about it, a record kept entirely separate from the raw files themselves, so that record can always be checked, corrected, or replayed from scratch. The FOH and Crane Crosscheck tools are small programs built specifically to make that job fast: they show you exactly which subjects need a decision, give you the information you need to make it, and remember every decision so it never has to be redone.
The raw folder is never changed — not once, not ever
Everything either tool does — picking a recording, tagging it, correcting a date or filename, even removing a subject from BIDS — happens only in the BIDS folder and its own bookkeeping files. Your raw folder is opened for reading only: nothing either tool does ever writes to it, renames anything in it, or deletes anything from it. That's true of every correction button, however it's worded — it only corrects how a name or date gets read when building BIDS from raw, never edits anything on disk in the raw folder itself.
That one rule is what makes everything else these tools do safe. Because every decision is recorded — never irreversibly baked into a renamed or deleted raw file — the entire BIDS folder, crosscheck decisions and all, can always be rebuilt from nothing but the raw folder plus those records. If the BIDS folder is ever lost, corrupted, or deleted by accident, nothing about your actual work is lost with it — see each tool's "Backing up, and rebuilding after a lost BIDS folder" section for how.
How this is different from QC
It's easy to mix these two up, since both involve looking closely at a recording — but they answer different questions, at different points:
- Crosschecking asks: "Is this the right file, correctly labelled, and has someone recorded that this decision was made?" It happens first, before any analysis.
- Quality control (QC) asks: "Is the data inside this file actually good?" — clean signal, sensible trial timing, no equipment glitches. That's a separate, later step: see EDA & SCRs, FOH Output Checks, and Crane Output Checks for the checks that happen once your data's actually processed.
Crosschecking always happens first: there's no point quality-checking a recording that turns out to be the wrong one.
Next: FOH Crosscheck or Crane Crosscheck — whichever matches your data.