Subjects were seated in a comfortable chair located in a dimly lit sound-attenuated RF-shielded room (IAC, Industrial Acoustics, Bronx, NY) in front of the computer monitor placed one meter away. EEG activity was recorded on a Neuroscan system (Version 4.1) (Neurosoft, Inc., El Paso, TX) using a multichannel electrode cap (Electro-cap International, Inc., Eaton, OH), which included 19 electrodes of the 10–20 International System and 42 additional electrode sites (Electrode Position Nomenclature, American Electroencephalographic Association, 1991), as shown previously (Jones et al., 2004). The electrodes were referenced to the tip of the nose, and the ground electrode was at the forehead (frontal midline). Artifact-free data obtained from the 7 posterior channels were included for genetic analyses of visual P3 amplitude.
