Community Review: BEP020 - Eye Tracking

[effigies]

We are pleased to announce the community review period for BIDS Extension Proposal (BEP) 020!

BEP020 extends the BIDS standard to formally specify eye-tracking recordings, which has previously been permitted but undefined in *_physio.tsv.gz files.

The draft specification may be found at: https://bids-specification--1128.org.readthedocs.build/en/1128/, and the eye-tracking specification may be found in the Physiological recordings section.

The proposed changes may be found at #1128. To view the source difference, click the Files changed tab.

Example datasets may be found at:

• eyetracking_binocular
• eyetracking_fmri

Procedure

Review period

Community review is open from September 29 - October 10, 2025.

Voting

This discussion is a poll, which you can vote in once and cannot change your response. Therefore, please vote once you are satisfied that your answer will not change.

If you vote "No", you may create a thread to explain your reasoning or send a private email to bids.maintenance [at] gmail.com so that your position can be fully understood.

How to review

Use threads in this discussion to request clarification or changes to the BEP. Each independent topic or proposed change should have its own thread. Please review existing threads and consider adding comments to those, if your topics are already being discussed. If your concerns are adequately represented by an existing comment or comments, consider using the 👍🏻 reaction button to indicate agreement in place of extending the discussion.

Where possible, propose the specific text you would like to see added or removed.

For minor issues, such as typos, feel free to make code suggestions only, using the suggest feature on the BEP020 pull request. These suggestions may be accepted or rejected without discussion, so do not make substantial proposals in this way.

Finalization

Once the review period is finished, the BEP leads and maintainers will consider the entire discussion, identify outstanding points to be resolved, and work toward finalizing the BEP. Community members may be asked to participate in this process to provide the necessary expertise.

Before being merged, the BEP will be integrated into the BIDS validator, and the examples must pass the validator.

This is the first of three review periods scheduled for this fall. A BIDS 1.11.0 release is anticipated in December 2025/January 2026 if any BEPs are merged during these periods, regardless of the conclusion of this specific BEP.

If, for any reason, a critical issue is found after the BEP is merged, the BEP will be reverted while the issues are addressed. At the discretion of the BIDS steering group and maintainers group, depending on the scope of changes, a new community review period may be opened.

[VisLab]

I wanted to raise a concern that wasn't addressed in the issues, so I voted no. However, I am strongly in favor of including eye tracking into BIDS. and appreciate all the work that the proposers have done to bring this important proposal forward.

My concern is that eye tracking has been demoted ---I feel that consideration should be given to making it the "eye" modality for these reasons:

1. Eye tracking is important in its own right as a way of measuring participant responses (eyes are after all the windows to the soul), and eye-tracking will be increasingly available in a variety of commercial as well as laboratory devices, lowering the barrier to including it in experiments.
2. Eye tracking measurements and the required metadata are spread over a number of files and they have their own event files and JSON sidecars.
3. There is no standard place to put them in the proposal. This is problematic in multi-modal experiments -- which one of the modalities gets the eye-tracking?
4. The separate modalities makes it easier to ascertain what kind of data a dataset contains. I feel that the current proposal somewhat violates the basic organizational principles of BIDS.

[m-miedema]

@VisLab I agree with point 3, though we hope this will be resolved in BEP 045 (Physio), which would allow an umbrella physio modality to also hold eyetracking.

[effigies]

@VisLab Apologies for the long delay. We have discussed your comment among the BEP leads, maintainers and steering.

We do not agree that eye-tracking has been demoted, but that an opportunity to promote it was not taken in this BEP. Eye-tracking data was specified in BIDS 1.0 as belonging in _physio.tsv.gz files that accompany primary data files. BEP20 is a parsimonious expansion that specifies how to record eye-tracking data, but makes no attempt to address the general problem of simultaneous modalities.

We also agree that BEP045 is likely a better location to make broader changes that address all physiological recording types, and hope you will engage there.

[bgagl]

Thanks for all the work. It looks great! Only two minor issues caught my eye ;)

• Some systems provide only pupil diameter, preventing accurate pupil area calculation. One could add this option.
• Gaze-contingent experimentation is not documented. One key advantage of eye-tracking is the implementation of gaze-contingent experiments (i.e., the simplest version would be an explicit fixation control before the start of an experiment). I'm not sure how this would be done optimally, but at least at the metadata description level, it should be able to be integrated.

[effigies]

Thank you all for your thoughtful reviews. We will be rereading carefully over the next few weeks to be sure that all concerns are addressed. If necessary, we will reach out to individual reviewers for further discussion.