Severe antisocial behaviour can be observed across a wide span of disorders, including conduct disorder and antisocial personality disorder. Within the spectrum of antisocial disorders there is a group of individuals classified with psychopathy, which has traditionally been typified by disturbances in affective functioning combined with severe antisociality. In the past two decades, disturbed functioning in these two domains has been assessed with the Psychopathy Checklist-Revised (PCL-R; 
), which has been the golden standard for the assessment of clinical psychopathy. The PCL-R measures behaviour reflecting interpersonal-affective functioning and antisociality and yields a total score indicating the presence of psychopathy. Studies assessing the cognitive counterparts of these behavioural indexes have linked psychopathy to impaired processing of affective information 
, and to disturbances in other non-affective cognitive domains such as learning 
and attention 
. In contrast, non-psychopathic antisocial behaviour has been linked to a broader range of problems in executive processing relative to psychopathy 
. The latter points out that while the concepts of psychopathy and generic antisociality show overlap on the behavioural level, they seem to differ in the cognitive processes that are affected and the extent to which these are deficient.
Attention is one of the cognitive processes that have been investigated extensively in comparative studies between psychopathy and non-psychopathy. There are numerous behavioural results indicating abnormalities in attentional processes that seem to be unique to PCL-R diagnosed psychopathy compared to non-psychopathic antisociality 
. In contrast, relatively few studies have examined the electrophysiological correlates of attention in psychopathy 
. A recent study using event-related potentials (ERPs) found that the abnormal allocation of attention in psychopathy seems to be due to disturbances at an early stage of selective attention, reflected by an increased positive ERP around 140 ms after stimulus presentation (P140; 
). These ERP results were interpreted as additional support for the Response Modulation (RM) theory, which predicts that psychopathy is related to a tendency to over-allocate attention to goal-relevant information and to ignore potentially relevant secondary information. Apart from these early effects, selective attention is also involved in later stages of processing 
Previous ERP studies on attention in psychopathy have mainly focussed on this later aspect of attention by looking at components belonging to the P3-family 
. The term P3-family refers to a conglomeration of ERP components with a positive deflection occurring in a separate, much later time-window than the P140. The components belonging to the P3-family have been implicated in various functions such as attentional processing 
, inhibition 
and error-processing [e.g. 16]. Two P3 potentials have been shown to be modulated by attentional allocation and task demands 
. These components can be assessed using the oddball paradigm, in which infrequent target stimuli are presented in a string of frequent nontarget stimuli. Voluntary detection of the infrequent target stimuli elicits a P3 with a parietal distribution, also known as the P3b 
. A variant of this task, the three-stimulus oddball paradigm, also includes the occurrence of highly salient task-irrelevant novel stimuli. In this version, participants respond to infrequent target stimuli but withhold their response to both infrequent novel and frequent standard stimuli. Task-irrelevant novel stimuli are known to elicit a P3 with a frontocentral distribution termed the P3a (or the novelty P3) 
. The P3a reflects an involuntary automatic orienting of focused attention to novel stimuli and this mechanism is governed by anterior cingulate cortex (ACC) 
The results of the aforementioned studies on the P3 potentials in individuals with PCL-R diagnosed psychopathy have been inconclusive. Jutai et al. 
investigated the P3b under single-task and dual-task conditions and did not find differences in amplitudes. In contrast, Raine and Venables 
employed a continuous performance task and reported enhanced P3b amplitudes in subjects scoring high on psychopathy. Later studies by Kiehl et al. 
found the P3b to be reduced in psychopathic samples compared to non-psychopathic incarcerated offenders, as did Gao et al. 
in a community sample of unsuccessful (caught) psychopaths. In sum, the P3b has been found to be reduced, normal and enhanced in samples scoring high on psychopathy.
Until now, only two studies specifically investigated the frontal P3 to novel oddballs in psychopathy 
. Kiehl et al. 
reported the P3a to be reduced, but only in one of the two psychopathic samples tested and no differences were found in the other sample. Gao et al. 
reported no differences in P3a amplitudes between controls, successful (uncaught) and unsuccessful psychopaths. Furthermore, a study on another frontal P3 component known as the NoGo P3 found reduced amplitudes in psychopathy 
, while a more recent investigation found the NoGo P3 to be unaffected in psychopathy 
. Thus, the results on frontal components are also contradicting. One general explanation for these mixed results might be that the different tasks used tap into slightly different cognitive processes and these discrepancies are in turn reflected by differences in ERPs (for more details see 
). In short, more research on the relationship between the P3s and PCL-R diagnosed psychopathy is needed in order to increase our understanding of these inconclusive results.
In sharp contrast to psychopathy, P3 findings in various non-
psychopathic samples related to antisocial behaviour have shown much more convergence. In general, both the P3a and the P3b tend to be reduced in these populations, which include disorders such as substance abuse disorder 
, conduct disorder 
, and populations at risk of developing these types of disorders 
. A recent meta-analysis found a negative relationship between antisocial behaviour in general and the P3 
. It was suggested that the reduced P3 in antisocials reflects faulty utilization of neural resources, resulting in hampered processing of relevant information. However, it was pointed out that this deficiency might be less prominent in psychopathy. These results highlight the need to establish how well each of these two groups can recruit neural resources in order to process information that is relevant to the task at hand.
As processing of information is continuous and dynamic, one approach is to regard the P3 components as electrophysiological manifestations of neural recruitment during this process. More specifically, the automatic orienting of focussed attention reflected by the P3a facilitates the allocation of attentional resources to successive memory storage operations in the hippocampal formation. The output is then passed on to the parietal cortex. This latter, controlled attentional process in parietal regions is reflected by the P3b 
. This interactive mechanism between frontocentral and parietal areas is indicative that monitoring events is a continuous process. Although the distributions are frontocentral for the P3a and parietal for the P3b, an electrophysiological response to targets can also be observed in frontocentral areas, albeit smaller in amplitude relative to novels. The opposite pattern can be observed in parietal areas. More specifically, the P3 to novels is larger than the electrophysiological response to targets in frontocentral areas, while the P3 to targets is larger than the response to novels in parietal areas. To our knowledge, this dynamic switch in electrophysiological pattern resulting from the interplay between frontocentral and parietal areas has not been explicitly assessed before in either healthy or patient samples. Examining whether the switch in pattern is present in the ERPs to targets and novels in frontocentral in relation to parietal regions could yield valuable information about the quality of neuronal recruitment and the extent to which the cognitive processing driving these potentials are functionally affected. Thus, the current approach offers a more sensitive electrophysiological measure for examining and comparing the quality of cognitive processing in psychopathic and non-psychopathic clinical samples.
The main goal of the present study was to assess cognitive processing of rare novel and target events in psychopathy relative to a non-psychopathic sample of institutionalized offenders and a group of matched healthy control individuals. Based on the converging findings in non-psychopathic samples, a diminished P3a to novel stimuli was expected in non-psychopathic offenders compared to both psychopathic and healthy individuals. In contrast, due to the lack of group differences in the majority of the samples in which a frontocentral P3 was assessed in clinical psychopathy 
, combined with reports on intact automatic processing in ACC 
, the P3a was expected to be intact in psychopathic subjects relative to the non-psychopathic participants (thus similar to healthy controls). Second, reductions were found in three out of five reports on the P3b in psychopathy and in a large amount of studies in non-psychopathic samples of antisocials, and we subsequently predicted reduced P3b amplitudes in both non-psychopathic and psychopathic offenders relative to healthy controls. Finally, the quality of processing and attentional allocation during the continuous monitoring of infrequent stimuli was also investigated in the offender groups by examining the switch in the pattern of the ERPs to targets and novels in frontocentral and parietal areas.