For the analysis of the responses on the SAM scale, there was a significant difference in undergraduate sample for the affective condition compared to the neutral and semantic conditions in valence ratings but not in arousal ratings. There were no significant differences in the reported levels of arousal and valence between psychopaths and non- psychopaths. Both groups rated the stimuli in the affective condition as more positive in valence although this did not reach statistical significance. Thus these results validate the earlier hypothesis and paralleled those of other research (Patrick et al., 1993, 1994, Kiehl et al., 1999, Williamson et al., 1991), which have found that no differences in the ratings of emotional stimuli between psychopathic and non-psychopathic controls. It appeared that psychopaths were indeed capable of identifying and providing normal ratings of stimulus intensity and pleasantness or unpleasantness though they probably might not be able to process such information in an empathetic fashion.
For the undergraduate sample, the rate of accuracy was significantly lower to the semantic condition as compared to the neutral and affective conditions whereas for the reaction time data, undergraduates here showed no differences across all three conditions.
In the incarcerated sample, psychopaths were not significantly different from non- psychopaths in terms accuracy or reaction times. All three samples, the undergraduates, the psychopaths and the non-psychopaths, had longer reaction times and decreased accuracy rates to the neutral/non-living (cognitive mismatch) condition, with the most marked effect observed in psychopaths. The reaction times to the affective /living (affective mismatch) condition showed behavioural response slowing also although it did not comprise accuracy levels. This would support the idea that emotional stimuli in this paradigm served an ‘interrupt’function.
4.3 Affective processing in psychopaths vs non-psychopaths
The N2 amplitude was the most negative at the parietal lead in the undergraduate sample. Psychopaths did not show enhancement of the N2 amplitude while non- psychopaths showed greater N2 negativity to the affective condition. In line with the idea of an anterior dysfunction, psychopaths exhibited a less negative N2 prefrontally than non-psychopathic individua ls. Moreover, psychopaths showed less nSW enhancement than non-psychopaths and undergraduates at the affective condition. The greatest nSW negativity observed was at the parietal region and it gradually diminished as it moved forward to the anterior regions. This trend is similar for psychopathic inmates, non- psychopathic inmates and undergraduates.
The N4a component has been found to be an ERP marker for mismatch stimuli in a previous context (Kutas and Hillyard, 1980, 1984, Kutas and Van Petten, 1988, and Ganis, Kutas, and Sereno, 1996). In this study, the greatest negativity in the early and late
N4 was attributed to the affective mismatch condition in the undergraduate sample. In the prison sample, the early and late N4 exhibited no group difference and the N4s were also enhanced to the affective mismatch condition, similar to those in the undergraduate sample. This supports the idea that the affective mismatch modulates the N4 component, both early and late N4, more than the semantic mismatch. As the affective mismatch was latent, the N4 enhancement does not require conscious processing in order to occur. This is consistent with the idea that ERPs are subconscious signatures that reflect activity in specific brain circuits. The lack of N4 group differences between psychopaths and non- psychopaths is suggested to be reflective of the level of arousal in the stimuli (Lim, 2001).
Since the intensity of arousal was not experimentally manipulated, this could well explain why there were no group differences seen at the early and late N4.
4.4 Cognitive processing in psychopaths vs non-psychopaths
In the current study, the semantic mismatch condition generated the greatest P3 amplitude for the psychopathic inmates, non-psychopathic inmates and undergraduates.
However, at the prefrontal and frontal sites, psychopaths had a higher P3 amplitude than non-psychopaths. These results provide further evidence that psychopaths and non- psychopaths do differ in terms of frontal lobe processing and ties in with other research that report that psychopaths exhibit a smaller N2 (Kiehl et al., 1999) and a larger P3 in response to affective stimuli (Raine and Venables, 1988) and provides partial support for Raine’s (1998) suggestion of a novelty seeking hypothesis in psychopaths.
4.5 Neuroaffecive processing in psychopaths
The ERP results in this study validate the reality of the different psychopathy factors, in particular the 3-factor PCL solution proposed by Cooke and Michie (2000).It raises the possibility that the social deviance factor (factor 2 on Hare’s 2-factor PCL
solution) and impulsivity factor (factor 3 on Cooke and Michie’s 3-factor solution) may reflect insults to the frontal lobes (Neo, 1991). The affective deficiency factor on the other hand may be more inherent. The affective deficiency is thus more of a biological or neurological dysfunction (Deckel, Hesselbrock and Bauer, 1996, Gorenstein, 1982, Hare, 1984, Lapierre et al., 1995, Intrator et.al, 1997) than it is a case of ‘acquired sociopathy’
(Blair and Cipolotti, 2000) or pseudopsychopathy..
Psychopaths, however, do not show a deficit across all ERP components. At the N4 epoch, the ir ERPs are similar to those of non-psychopathic inmates and undergraduates. It is possible that the N4 reflected more arousal aspects of the affective stimulation (Lim, 2001). If this is the case, it is consistent with the idea that the amygdala is possibly the generator of the N4 (Howard, 2001) as the amygdala has been closely associated with the processing of negative affect, for example, fear and disgust (Ado lphs et al., 1999 and Whalen, 1998). If the N4 reflects reception of a signal from the amygdala to switch on cortical processing, the results in this study imply that the switch is functioning properly but that the ensuing cortical arousal (as indexed by the nSW) does not eventuate.
The stud y illustrates that ERPs are useful as indices of ne uroaffective processing.
Psychopaths demonstrate that they are insensitive to emotional mismatch as indexed by the N4a and the N4b but are unable to process the emotional information as reflected by the N2 and nSW. They also imply that psychopaths are globally deficient in affective processing as their neuroaffective processing dysfunctio n is not confined to negative or high arousal stimuli (Blair et al, 1995, 1997, Lykken, 1995 and Newman, Patterson and Kosson, 1997) but instead shows up in affective processing whether the stimuli is positive or negative and hence is more of a global affective deficit (Damasio, 1994, Herpertz et al.,
2000 and Kiehl et al., 1999) as it would seem that the N2 and nSW components, as compared to the early and late N4 components, reflect different aspects of emotional information processing.
4.6 Conclusions
The study casts some light on our understanding of the processing dsyfunction in psychopathy. Psychopaths are shown to be globally deficient in neuroaffective processing, disconfirming theories of specific affective dsyfunction such as the low fear (Lykken, 1995) or lack of responsiveness to distress cues (Blair et al., 1995, 1997) while having intact cognitive processing abilities. The study sheds light on the neural processing differences between the psychopaths and non-psychopaths , especially at the prefrontal site, provid ing support for an anterior dys function in psychopathy. This dysfunction could possibly be an orbito frontal cortex dysfunction as implied by other research in the area (Deckel, Hesselbrock and Bauer, 1996, Intrator et al., 1997, Raine et al., 1998, 2000 and Soderstrom et al., 2000, 2002).
4.7 Limitations
One of the limitations of the study is that it did not employ negative valence stimuli with which the processing of positive valence stimuli could be compared. The experiment needs to be repeated using both negative and positive valence low arousal stimuli in separate sessions so as to compare the neuroaffective processing of these stimuli. Only then would it be possible to investigate if the N4 was responding only to arousal or simply to negative stimuli.
Only a small region of the scalp was investigated and thus there was no opportunity to assess effects of laterality and thus issues of hemispheric asymmetry.
Further studies could be done using dense electrode arrays so that source analysis can be
carried out. Functional imaging tools, such as magnoencephalography and functional magnetic resonance imaging, could be emplo yed along with high density ERP tools so that the neural generators of the ERP waveforms can be more precisely identified
4.8 Directions for future research
The findings suggest psychopaths and non-psychopaths process affective and cognitive information differently and this is revealed electrophysiologically. These may stem from a processing dysfunction in psychopaths for affective stimuli and may help us design better tools to identify psychopaths. Such an electrophysiological tool would be an advantage over current tools such as interviews that are often subjective and prone to issues of social desirability.
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