Katrina Sifferd and William Hirstein, in their paper ‘On the criminal culpability of successful and unsuccessful psychopaths’, argue that neuropsychological data show that unsuccessful psychopaths have diminished mental capacities that warrant a partial or diminished responsibility defence. We respond that the currently available neuropsychological evidence does not warrant their conclusion that unsuccessful psychopaths should not be deemed completely legally responsible. Instead, we maintain that the current state of this type of research suggests that psychopaths might be suffering very specific cognitive impairments. However, the impact that these impairments might have on the specific criminal behaviours that courts have to assess is far from clear.
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In fact, as we show below, Sifferd and Hirstein are mistaken in grounding the correlation between unsuccessful psychopaths and below normal EF on Ishikawa et al.’s  study.
An explanation why people who are born without the corpus callosum do not exhibit behavioural deficits is the fact that during development their brains manage to learn how to transmit information form one hemisphere to the other by utilizing some alternative pathways [13, p. 185]. Similarly, there is evidence that core psychopathic traits are highly heritable [2, ch. 1], it could be that through development psychopaths’ brains learn to solve different EF tasks even though they show abnormal functioning in the brain areas that normally subserve EF.
A reviewer of this journal has interestingly noted that in the Ishikawa et al. study, there is some reported raw data according to which there is a positive correlation between lower performance on the WCST and unsuccessful psychopathy. However, in their study, as indicated by the quote above, Ishikawa et al. do not take these raw data as relevant since these differences vanish after the IQ scores of the participants have been taken into account. In any case, Sifferd and Hirstein do not appear to rely on these raw data. Instead, it seems that they couple their incorrect reading of the main conclusion of Ishikawa et al. study with the claim that this result is robust even when participants’ IQ’s have been matched.
Thus, we do not find the inconsistency in results significant because we think that there is something methodologically wrong with the studies on which Sifferd and Hirstein rely. We argue that once a plausible explanation for the mixed results is on the table, then we should see that they do not provide sufficient data for thinking that unsuccessful psychopaths, unlike successful ones, should be held less legally accountable. We thank an anonymous reviewer for nudging us to be more explicit about this point.
In fact, Roald Maes and Inti Brazil  in their review study argue that, despite the appearances, there is no plausible evidence that there is a group of psychopaths who have superior EF.
We thank an anonymous reviewer for pressing us to bring the claim in this paragraph to the foreground.
In fact, the issue whether the PCL-R should be divided into two or more factors is still debated among the psychopathy researchers . For an overview, see, . We do not take sides on this issue. However, it has to be noted that not all researchers agree that factorization of psychopathy measures implies disunity in the construct of psychopathy. For instance, Robert Hare [22, p. 50] contends that PCL-R, despite its factorization, measures a unitary construct. On the other hand, Jalava, Griffiths, and Maraun argue that the factorization of PCL-R indicates that “there is no single, real, entity called psychopathy” [39, p. 194, see also, pp. 194–207].
According to Hare [22, p. 79], Factor 1 includes: Glibness and superficial charm; Grandiose sense of self-worth; Pathological lying; Conning/manipulative; Lack of remorse or guilt; Shallow affect; Callous/lack of empathy; Failure to accept responsibility for own actions. Factor 2 includes: Need for stimulation/proneness to boredom; Parasitic life style; Poor behavioural controls; Early behavioural problems; Lack of realistic, long-term goals; Impulsivity; Irresponsibility; Juvenile delinquency; Revocation of conditional release.
According to the original factor analysis, PPI’s 187 items were divided into 8 factors. These included Machiavellian Egocentricity, Social Potency, Coldheartedness, Impulsive Nonconformity, Blame Externalization, Carefree Nonplanfulness, and Stress Immunity [23, p. 44]. Later statistical analyses indicated that PPI could be divided into two factors. Social Potency, Fearlessness, and Stress Immunity form a factor that is nowadays called Fearlessness-Dominance. This includes traits such as absence of anxiety, willingness to take risks and skill at influencing others. Machiavellian Egocentricity, Impulsive Nonconformity, Blame Externalization, and Carefree Nonplanfulness form Factor 2 or Antisocial-Impulsivity traits. These include lack of concern for the social norms, attitude of indifference toward the future, and “a ruthless willingness to manipulate and take advantage of others” [23, p. 44]. These analyses also indicated that FD contains items that correlate with PCL-R’s Factor 1, while AI correlates with Factor 2 of PCL-R [21, 23].
Instrumental learning tasks involve learning to connect the valenced (positive or negative) value of stimuli to an action that is appropriate for solving the task. For an overview of these tasks as they apply to psychopaths in the present context, see .
We thank Neil Levy for pressing us to address this worry.
Of course, in this occasion, we have to leave open the issue whether they have abnormal affective or other mechanisms that might undermine their responsibility, especially by affecting specific moral competencies.
In this respect, the "Socratic" interviews done by philosopher Jonathan Glover and psychiatrist Gwen Adshead with the inmates of the Broadmoor Hospital are very suggestive. See, for instance, Glover’s recent book .
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Many thanks to Zdenka Brzović and Lovro Savić for reading and giving us valuable comments on different drafts of the paper. We would like to thank the two anonymous reviewers and Neil Levy, the editor of Neuroethics; their comments helped us to improve greatly this paper. In addition, we thank the organisers and participants of the following events, where parts of the paper were presented and discussed: Mente e medicina, Uniser, Pistoia, Italy 8/9/2016; Invited talk, Faculty of Media and Communications, Belgrade (Serbia), 9/6/2016; Conference: Ethical Issues: Theoretical and Applied, Bled (Slovenia) 6-10/6/2016; Invited talk, Donders Institute for Brain, Cognition and Behaviour, Nijmegen (Netherlands) 12/04/2016.
The Croatian Science Foundation (HRZZ) funds our research (project CEASCRO: grants n. 8017 and n. 9522).
Marko Jurjako and Luca Malatesti contributed equally to this work.
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Jurjako, M., Malatesti, L. Psychopathy, Executive Functions, and Neuropsychological Data: a Response to Sifferd and Hirstein. Neuroethics 11, 55–65 (2018). https://doi.org/10.1007/s12152-016-9291-6
- Executive function
- Legal responsibility
- Neuropsychological evidence