Skip to content

SDR-0005: Do not infer photometry channel identity from row position

  • Status: Accepted
  • Date: 2026-07-26
  • Decision owners: project maintainers
  • Related protocol/report: prospective IBL v0.2

Context

The prospective IBL query found 407 sessions from 18 new animals, but none had labelled 415-nm isosbestic rows. They instead alternated labelled 470-nm rows with wavelength-0 rows named None. ROI values were finite on both. Official IBL extraction semantics distinguish wavelength 0 (“No additional signal”) from 415 nm (“Isosbestic”). Treating finite values or alternating position as sufficient channel identity would pass a readiness gate only by changing the schema after it failed.

Decision

Require explicit wavelength/name metadata or primary acquisition provenance before assigning signal or reference semantics. Do not infer an isosbestic channel from row alternation, finite values, column position, correlation, or analytical convenience. Unknown channels remain unknown and must fail adapters that require a reference.

Consequences

Some large public cohorts cannot enter paired-reference workflows despite having apparently regular tables. This reduces immediate sample size but prevents silent scientific relabelling. Signal-only analyses remain possible only under separately declared methods and protocols.

Alternatives considered

  • Treat wavelength-0 rows as 415 nm because they alternate with 470 nm: rejected because official metadata assigns a different meaning and no primary provenance supports the reinterpretation.
  • Infer identity from correlation with 470 nm: rejected because correlation cannot establish acquisition wavelength or biological inertness.
  • Drop the reference requirement and run the frozen multiverse: rejected because all nine universes explicitly use reference correction.

Revisit trigger

Revisit for these assets if IBL publishes corrected metadata or acquisition-level documentation that identifies the wavelength-0 values as a specific optical channel.

Evidence added later

The producing ibllib version (2.38.0) explicitly maps wavelength 0 to “No LED ON”, and the associated study methods describe 470-nm-only acquisition with no isosbestic channel. The public archive does not expose the raw channel-map files, but the two independent primary sources agree. The paired-reference route is therefore closed unless new raw or corrected metadata appear. See the channel-provenance audit.