Stimulus-locked epochs (1200 ms, 200 ms prestimulus) were extracted. ERP waveforms were screened for electrolyte bridges (Tenke & Kayser, 2001). Channels containing amplifier drift, residual eye activity, muscle or movement-related artifacts, or noise for any given trial were identified using a reference-free approach (Kayser & Tenke, 2006a), and replaced by spherical spline interpolations (Perrin, Pernier, Bertrand, & Echallier, 1989) using the data from artifact-free channels if possible (i.e., when less than 25% of all EEG channels contained an artifact), as verified by visual inspection. ERP averages were computed for correct targets, nontargets, and novels (at least 16 trials for all averages), as well as for novels in the first and last halves of blocks (valid data containing at least 8 trials was available for 47 controls and 44 patients). ERP averages were then low-pass filtered at 12.5 Hz (− 24 dB/octave) and finally baseline corrected using the 200 ms preceding stimulus onset. Visual inspection of the individual ERP waveforms confirmed a satisfactory signal-to-noise ratio for each participant and each condition.
