Motion artifact

Signal disturbance caused by physical movement of the subject, electrodes or leads rather than by physiology. Mechanisms include mechanical disruption of the electrode-electrolyte double layer (a shifting half-cell potential produces large DC steps and low-frequency drift), triboelectric charge on flexing cables, and — for optical and magnetic sensors — displacement of the sensor relative to the head. Motion artifact dominates ambulatory, wearable and pediatric recordings and fNIRS, where head motion decouples the optode from the scalp.

Its signature is broadband and non-stationary but concentrated at low frequency and correlated with movement, so mitigation leans on hardware (active electrodes, low-impedance contact, strain relief, dry-contact designs) plus reference sensors: accelerometers, short-separation fNIRS channels, or the recording's own DC level used to regress or wavelet-clean the motion. ASR is widely used to suppress the large transient motion bursts in mobile EEG.