All six collaborating sites used identical experimental procedures and EEG acquisition hardware and software. Subjects were seated comfortably 1 m from a monitor in a dimly lit sound-attenuated RF-shielded booth (Industrial Acoustics Company, Bronx, NY, USA), and wore an electrode cap (Electro-Cap International, Inc., Eaton, OH, USA) as specified by the International 10-20 System for Electrode Placement (Fig. S2). The nose served as reference and the forehead served as ground. Electrode impedences were maintained below 5kW. Electrical activity was amplified 10,000 times using Neuroscan amplifiers and was recorded continuously over a bandwidth of 0.02-100.0 Hz on a Neuroscan system (Versions 4.1-4.5; Neurosoft, Inc., El Paso, TX, USA) at sampling rates of 256, 500 and 512 Hz, depending on the Neuroscan version, and stored for further analysis. During analysis all signals were re-sampled to 256 Hz and bandpass filtered between 0.05 and 55.0 Hz. Artifact rejection threshold was set at 100 μV. A minimum of 20 trials of 100 ms. pre-stimulus to 750 ms. post-stimulus artifact-free data for each stimulus was required for analysis.
