Artifacts were removed using the Gratton and Coles method implemented in BVA (Gratton et al., 1983). Data were highpass filtered with a cutoff frequency of 0.5 Hz using a zero-phase lag filter with a 48 dB/octave roll-off. Stimulus-locked trials were extracted for all instances where there was a correct behavioral response, for each of the three experimental conditions (target, rare non-target and standard non-target). Each trial comprised 450ms of data pre-stimulus and 1300ms post-stimulus. For ERP analysis, data were lowpass filtered with a cutoff frequency of 30 Hz using a zero-phase lag filter with a 48 dB/octave roll-off and baseline corrected using the 100ms pre-stimulus interval. Any trials containing out of range voltages (± 75 μV) were rejected as artifacts and excluded from further processing. Current source density (CSD) derivations were computed using a 4th order spherical spline and a maximum degree of the Legendre polynomial of 10 (Perrin et al., 1989). All further analysis were applied to both nose-referenced and CSD derivations.
