Continuous data were segmented into 1-s epochs every .5-s (50% overlap). After rejection of epochs contaminated by blink or eye-movement ( ±100 μV threshold, followed by interactive rejection), a reference-free approach identified isolated EEG channels containing amplifier drift, residual eye activity, muscle or movement-related artifacts (44), which were then replaced by spherical spline interpolations (45) from artifact-free channels whenever possible (i.e., fewer than 25% affected channels). Artifact detection and electrode interpolation was verified interactively, and accepted epochs screened for electrolyte bridges (46).
