The current study also replicated previously-reported findings of reduced P300 in relation to externalizing problems of various types. Replication of this finding here is noteworthy considering how the P300 response was elicited in the current study and how we quantified externalizing proneness. First, whereas prior studies documenting this relationship have measured P300 in relation to target stimuli in an oddball task (e.g. Gilmore et al., 2009; Patrick et al., 2006), P300 in the current study was recorded in relation to non-oddball, feedback stimuli. Second, in contrast with prior studies, in which externalizing has been operationalized in terms of specific impulse control disorders (e.g., Iacono et al., 2002) or as a composite of DSM symptom variables (i.e., conduct disorder, adult antisocial behavior, and alcohol, drug, and nicotine dependence; Patrick et al., 2006), we quantified externalizing proneness using a specially-designed questionnaire inventory (Krueger et al., 2007). Thus, the current work provides evidence that the finding of reduced P300 amplitude in high-externalizing individuals generalizes to multiple task conditions and methods of measuring this domain of psychopathology. By further exploring the P300-externalizing association across
