Color-singleton presence and color were determined per trial, such that each trial had a 75% chance of including a color singleton, and, in singleton present trials, there was a 50% likelihood that the color singleton would be red and a 50% likelihood it would be green. The visual search array was configured such that two of the six possible stimulus positions were located on the vertical meridian of the display. In each trial the target and salient distractor positions were randomly selected with the sole confine Transmembrane Transproters inhibitor that these stimuli be presented to different positions.

The search displays were presented on a CRT monitor located 60 cm. away from the participant’s eyes. Each trial began with presentation of fixation point for a random duration of 400 to 1400 ms. This was followed by presentation of the search array, which remained on the screen until 100 ms Selleck Selumetinib after response was made (when the next trial began). Participants completed 60 blocks of 30 trials, for a total of 1800 trials. They were instructed to respond as quickly as possible while maintaining an average accuracy of 90% or better, and feedback regarding accuracy and reaction time was provided at the end of each block. They were also instructed to maintain eye fixation throughout the experiment and told that eye movements were being monitored. Prior to beginning the

experiment, each participant completed at least one practice block. EEG and electrooculogram (EOG) were recorded from 134 sintered-AG/AgCl electrodes using the Biosemi ActiveTwo system (Biosemi, Amsterdam, the Netherlands). Horizontal EOG was recorded from electrodes located 1 cm. lateral to the external canthi and vertical EOG was recorded from two electrodes located 2 cm. above and below the right MTMR9 eye socket. Electrophysiological signals were digitized at 1024 Hz and resampled offline to 250 Hz. The data were high-pass filtered by convolving each channel with a Hamming-windowed finite

impulse response (FIR) function with half-amplitude attenuation at ~ 0.49 Hz and a 6 dB transition bandwidth of ~ 0.1 Hz, and low-pass filtered with a similar function that resulted in half-amplitude attenuation at 40 Hz and a 6 dB transition bandwidth of 8 Hz. ERP analysis was conducted using a combination of custom scripts for Matlab (Mathworks, Natick, MA) and the EEGLAB toolbox (Delorme and Makeig, 2004). Analysis began with the computation of independent components using the logistic infomax independent component analysis (ICA) algorithm (Bell and Sejnowski, 1995). The primary component associated with eye movements was identified and used to reject epochs in which participants moved their eyes, which resulted in the average rejection of 8.5% of total trials per subject (±3.6% SD). Following this all components associated with blinks, line noise, and other sources of artifact were removed from the data.