During the course of the study, three EEG acquisition systems were used, a 32-channel system (n = 7), a 40-channel system (n = 84) and a 64-channel system (n = 8). Midline electrodes were common across all systems, evidenced the maximal signal to noise ratio in the latency range of 75–200 ms, and are the subject of this report. The reference was the right ear for all recordings, and ground was 4 cm above the nasion for the 32-channel and 40-channel caps and 8 cm above the nasion for 64-channel caps. EEG data were acquired using the NuAmps (Compumedics Neuroscan, Inc., El Paso, TX) single-ended, 32/40-channel amplifier and Scan 4.2 Acquisition Software (Compumedics Neuroscan, Inc., El Paso, TX) for the 32-channel and 40-channel recordings. The NuAmps amplifier had a fixed range of +/−130 μV sampled with a 22-bit A/D converter where the least significant bit was 0.062 μV. For the 64-channel recordings, EEG data were acquired using the SynAmps2 (Compumedics Neuroscan, Inc., El Paso, TX) amplifier and Scan 4.3 Acquisition Software (Compumedics Neuroscan, Inc., El Paso, TX). The SynAmps2 amplifier
