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 had a fixed range of +/−333 μV sampled with a 24-bit A/D converter where the least significant bit was 0.019 μV. Electrode impedances were maintained below 10 kOhms. The sampling rate was 250 samples/sec. Data from control participants whose data were collected using the different amplifier systems (NuAmps, SynAmps2) were examined and revealed no differences associated with the different acquisition amplifiers. Vertical eye movements were recorded by electrodes above and below the left eye for later reduction of ocular artifact.
