Scalp to Source
Progress

Labs › w-reference-explorer

P1 mixed w-reference-explorer

Reference Explorer

Switch the reference on a real ERP and watch the waveform, the amplitude at a chosen electrode and the topography change together.

4 claims on this page are unverified. TODO(confirm) marks a specific statement the author has not yet checked against a primary source. Everything else on this page has been reviewed. Treat a marked claim as provisional and go to the cited source rather than quoting the sentence.

Modes: erp · topo · csd — the widget below runs in erp. Use Share state to put the exact view in the URL.

Reference Explorer

mode: erp
Loading Reference Explorer…

Data: ds-erpcore , subject sub-001, run task-P3, -0.19921875–0.80078125 s · license CC-BY-SA-4.0 · DOI TODO(confirm) · labels: algorithmic · a cropped, re-referenced or filtered derivative of the source recording. Share-alike. This asset is derived from a source whose licence requires that anything built from it carry the same licence. If you reuse it, distribute your version under CC-BY-SA-4.0 and keep the attribution below.
Kappenman, E., Farrens, J., Zhang, W., Stewart, A. X., & Luck, S. J. (2020). ERP CORE: An Open Resource for Human Event-related Potential Research. PsyArXiv. Paper DOI 10.31234/osf.io/4azqm. Dataset DOI 10.18112/openneuro.ds003069.v1.0.0, https://osf.io/thsqg/. Licensed CC-BY-SA-4.0; this is a derived asset and is distributed under the same licence (data/directory.yaml license_decision, section 13 item 15).

What it does

One real ERP, several references. Pick a reference — the original recording reference, average, linked mastoids, Cz, REST — and the waveform panel, the amplitude readout at the selected electrode and the scalp map all update from precomputed evoked arrays. A time cursor moves through the epoch; a condition selector switches between the two conditions and their difference. In csd mode the current source density transform is shown alongside, with its own units.

All the heavy work is done in Python: the evoked arrays under each reference, the CSD transform and the spherical-spline topomap interpolation matrix are precomputed. The browser multiplies the interpolation matrix by the channel weights and draws.

Controls

ControlWhat it sets
ReferenceOriginal, average, linked mastoids, Cz, REST
ConditionTarget, standard, or the difference wave
ChannelWhich electrode the waveform panel and amplitude readout follow
Time cursorThe latency at which the topography is drawn
CSD toggle(csd mode) show current source density beside the referential map, in µV/m²
Scale lockKeep the amplitude and colour scales fixed while the reference changes, so the change is comparable

What to look for

erp

  • The amplitude at a fixed electrode and a fixed latency changes with the reference — sometimes by a large fraction, occasionally in sign.
  • A reference site that carries the component attenuates it: Cz sits near the P3’s own maximum, the mastoids are not electrically silent for posterior and temporal generators.
  • The difference wave is far less reference-dependent than either condition alone, because the common reference term largely cancels.
  • Nothing about the shape of the waveform’s relationship to its neighbours changes; what changes is the constant subtracted from every channel at each time point.

topo

  • Re-referencing shifts the whole map up or down at each time point: the gradient is preserved, the zero-crossing moves, and a colour scale centred on zero makes that look like a different map.
  • With the scale locked, the pattern of differences between electrodes is visibly identical across references.
  • Coverage matters: an average reference over a montage that stops above the ears is an approximation, and the map shows which regions the average is not sampling.

csd

  • CSD is reference-free by construction — switching the reference leaves the CSD map unchanged.
  • It sharpens topographies and suppresses volume-conducted spread, at the cost of amplifying high spatial frequencies (including noise from a single bad channel).
  • Its units are µV/m², so its amplitudes are not comparable with any referential measurement.

Used in

  • L2.3 Re-referencing (erp)
  • L3.4 Topographies and scalp maps (topo)
  • L5.3 Surface Laplacian and CSD (csd)

Data provenance

ds-erpcore — ERP CORE (Kappenman et al., 2021), CC BY 4.0, open access, per-subject downloadable. Biosemi ActiveTwo, 30 EEG + 3 EOG electrodes in a 10-20 placement scheme, 1024 Hz, CMS reference, 60 Hz mains, no software filters, 40 participants per paradigm. The shipped arrays are grand-average evoked responses for the P3 paradigm, derived (epoched, baselined, re-referenced, resampled) and attributed; each reference is a separate asset, and the topomap interpolation matrix for the 30-channel montage lives in the shared folder so that the ERP widgets do not each ship their own.

TODO(confirm): the author mirrors the ERP CORE entry into data/registry.yaml (§10.11 item 8) and signs off the dataset page.

TODO(confirm): REST requires a forward model. If one could not be built inside the asset budget, evoked.json marks the REST entry TODO(confirm) and the widget offers the remaining references; the frame’s provenance line and the JSON are the authority on what actually shipped. Per-subject variants ship alongside the grand averages only if they fit the §4.5 budget.

Open the code

site/src/components/widgets/w-reference-explorer/ — Widget.svelte, index.ts, README.md. Repository link: TODO(confirm) (GitHub org/repo, §13 item 3).