The finding that P3-related sequence effects are normal in those with an EXT disorder suggests that such individuals are able to effectively utilize context during the oddball task to form subjective expectancies about the probability of a target occurring. This ability to utilize context occurs despite previous findings of diminished attention and working memory abilities in EXT spectrum disorders (e.g. Barnett, et al., 2009; Bogg & Finn, 2010; Finn, 2002). It may be the case, however, that the oddball task is relatively easy, such that those with an externalizing disorder can compensate for the relatively low working memory and attention requirements. Previous studies showing compromised working memory and attention abilities in EXT disorders have used comparably more difficult measures, e.g. the Digit Span, Operation-Word Span, Spatial Span, and Auditory Consonant Trigram tests (Barnett, et al., 2009; Bogg & Finn, 2010; Finn, 2002). Thus, while the underlying neurophysiology responsible for P3-AR in EXT may be compromised, the concomitant executive functioning abnormalities may not be manifested unless the related cognitive systems are sufficiently taxed. This interpretation is consistent with other studies showing abnormal brain activity alongside normal task performance in EXT spectrum disorders (e.g. Caldwell et al., 2005; Tapert et al., 2004).
