For the ERP data, blinks and other ocular artifacts were corrected using the method of Gratton, Coles, and Donchin (1983). Trials with activity >100 µV were excluded from further processing. ERP epochs, consisting of 2 s of data, including a 500 ms prestimulus baseline, were averaged over the easy and hard target conditions at each of the three electrode sites. P3 amplitude was defined as the point between 280 and 600 ms at which amplitude of the average waveform was maximal.
