Our finding that the P3-AR effect was not secondary to a contextual processing deficit also rules out another possible explanation for why P3-AR is associated with EXT. We found that all participants, including those high in EXT, showed the expected association between the number of standards preceding a target and P3 amplitude. This finding, along with our results showing no significant relationship between EXT and either reaction time or task performance, indicates that all participants were effectively engaged in the task, paying attention and processing the stimuli. Hence, the P3-AR effect cannot easily be attributable to uncooperativeness, poor motivation, or superficial inattention. Thus, P3-AR appears to tap a core dysfunction, lending further support to its status as an endophenotype indexing genetic risk for EXT.
