The Fixation and Saccade P3 Figure 4. Comparison of fixation and saccade P3s. When P3s in saccade and fixation conditions are compared, saccade related EOG and EEG activity cancels in the saccade target minus saccade distracter subtraction, and there are no significant differences observed between saccade and fixation conditions. A, Grand average across subjects of P3 signal (target minus distracter) at midline electrodes Fz, Cz, Pz and Oz. Time is measured relative to image presentation (fixation condition) or relative to saccade landing (saccade condition). Shaded area represents standard error. B, Topographies of target minus distracter difference in saccade and fixation trials. doi:10.1371/journal.pone.0048761.g004 P3 in Fixation and Saccade Trials In Figure 2, it can be seen that in all but one subject, both the central fixation trials and the saccade trials yielded significant clusters of positivity of target trials relative to distracter trials at the p = 0.05 level or less (one-tail cluster statistic). The one exception was subject 7, for whom the fixation task yielded a P3 with p = 0.23 and a saccade P3 with a false alarm probability of p = 0.074. Since no significant fixation or saccade P3s were observed in S7, this subject’s data were not included in cross subject analyses in which the fixation and saccadic P3 were compared. (It was noted during data collection that there was an abnormally large amount of low frequency drift artifact in S7’s EEG data, therefore resulting in large trial-to-trial variability. This low frequency drift was likely the reason that the fixation and saccade P3s did not reach significance in S7.). The spatial topography of the P3 in both the saccade and the fixation case was widespread on the scalp. 6261 electrodes belonged to significant clusters of P3 activity in the fixation condition and 5962 electrodes belonged to significant clusters of P3 activity in the saccade condition on average across subjects. PLOS ONE | www.plosone.org 8 November 2012 | Volume 7 | Issue 11 | e48761