MEG Artifact Detector — specifics¶
Menu Process → Signal → MEG Artifact Detector 1.0.0. See the shared methodology for the five criteria and the common parameters — this page only covers what's specific to MEG.
Neighbors: 3D nearest sensors¶
Criteria 2 and 3 need a notion of "neighbor". For MEG this is a plain 3D nearest-neighbor search
using each sensor's position (neighbor_count sensors, default 5). MEG sensor arrays are a single
rigid, densely and evenly sampled surface, so Euclidean-nearest is a simple and meaningful choice.
If channel positions are unset (e.g. a raw file opened without its sensor layout), criteria 2 and 3 are skipped entirely with a warning — "nearest neighbor" has no meaning without positions.
PSD frequency bands — fixed, validated¶
Unlike its EEG/sEEG siblings, the broadband range (criterion 3) and the peak-search range (criterion 4) are not exposed as parameters for MEG:
| Criterion | Range | Notes |
|---|---|---|
| 3 — broadband power vs. neighbors | 100 – 500 Hz | |
| 4 — own-baseline peak | 20 – 800 Hz | 8 Hz baseline-smoothing window |
These were fixed once validated against a real recording (see below); there is currently no parameter to change them.
Validation¶
MEG Artifact Detector was validated end-to-end against a real 4D/BTi (248-magnetometer) recording with a known set of bad channels:
- every channel in that file's own bad-channel list was correctly flagged;
- the detector correctly avoided flagging channels the ground truth considered healthy;
- one additional flagged channel was confirmed, on visual review of the raw trace, to be a genuine — if previously unlisted — artifact.
The default thresholds described on the shared methodology page and the fixed bands above reflect that validation.
Command line¶
--run "MEG Artifact Detector" — see using these plugins from the command line.