Taken together, the current results indicate that individuals high in externalizing proneness process external performance feedback normally in terms of post-stimulus theta-FRN activity, generally associated with performance monitoring. Importantly, this suggests that participants across the range of externalizing proneness were similarly engaged in processing the feedback at this level. However, the reduction in delta-P300 response, continuing somewhat later in the post-feedback interval, indicates that there is an aspect of sustained feedback processing (i.e. continuing after the theta-FRN, and associated with P300) that is abnormal in individuals high in externalizing proneness. Further, this P300 amplitude reduction appears to be more general than specific – occurring robustly to both Gain and Loss feedback stimuli in this simulated gambling task, as well as in standard oddball tasks. This suggests that such observed P300 amplitude reductions may not be related to specific cognitive functions often associated with target P300 in oddball tasks, and that some more general process may be involved.
