The relationship between deficits on neuropsychological measures of EF and real- world EF tasks is complicated. Neuropsychological measures are necessarily designed to
tap into simple tasks that look at a particular aspect of EF, whereas real-world tasks that involve EF are complex and involve numerous processes (Ogilvie et al., 2011). Therefore, it is plausible that someone who does not display deficits in neuropsychological measures may still encounter difficulty in day-to-day tasks that require complex executive control. The lack of ecological validity of traditional neuropsychological measures has been largely criticized (Goldstein, 1996; Sbordone, 1996). In response, complex batteries of tests are being developed in order to assess all components of EF, like the DKEFS (Delis et al., 2001; Ogilvie et al., 2011).
Further complicating things is the lack of ubiquitous definition of EF, which may lead to atheoretical approaches in research. Most measures of EF were developed and based on theoretical models of EF (Chan, Shum, Toulopoulou, & Chen, 2008). Using a theoretical framework to approaching EF research can facilitate an accurate, specific, and sensitive assessment of EF. Research using the DKEFS often cites different component scores (e.g., Hancock et al., 2010). Since each subtest of the DKEFS provides between 6 and 34 interpretable scores (Delis et al., 2001), researchers need to carefully consider which components make up the construct of EF.
Additionally, EF research typically is concentrated in the experimental realm, which has been heavily criticized (Chan et al., 2008). Although clinical populations commonly display EF difficulties on neuropsychological measures, the manifestation of these difficulties in real-world scenarios has not been acknowledged. This functionality needs to be addressed, particularly when discussing rehabilitation and reintegration of offender populations. Burgeoning research shows that EF remediation programs are effective at improving EF (e.g., in mental disorders; Deckersbach et al., 2010; Solé et al., 2015; Wykes et al., 2011). However, the outcomes of rehabilitation programs should not
be only measured by test score improvement, but by reduction in everyday difficulties related to EF.
The lack of a common definition of violence and aggression highlighted in this thesis may account for differences in the relationship between EF deficits and violence and aggression across the literature. Given the heterogeneity of offenders in both criminal populations, the etiology and psychosocial predictors of crime is difficult to determine in these populations. Furthermore, violence and aggression are typically considered in reference to intent. While intent may be easier to distinguish in a correctional population, the presence of a mental disorder in a forensic psychiatric population makes intent almost impossible to distinguish. Therefore, the definition of violence and aggression in the current studies were behavioral, which — while appropriate (Eichelman & Hartwig, 1990) — are different than the definitions used in some previous research. In order to account for the varying definitions of violence and aggression, the current study looked at violence and aggression in numerous contexts (i.e., historical violence, index offence, and in-custody aggression).
4.6 Limitations and Future Directions
Despite the potential of EF in determining violence and aggression in criminal populations, a few limitations need to be addressed.
Factors Influencing EF. Numerous factors may affect EF and the relationship between EF and violence and aggression in both criminal populations, including
psychotropic medication (e.g., Blyler & Gold, 2000), age of first offence (Nieuwbeerta, 2001), personality disorders (Fullam & Dolan), and intelligence (Heilbrun & Heilbrun, 1985; Henry & Moffitt, 1997). Personality factors may be an important contributor to violence and aggression above mental disorder or neuropsychological function (Fullam &
Dolan, 2008). Furthermore, those higher in psychopathy have more profound EF dysfunction than non-psychopathic offenders (Hildebrand, De Ruiter & Nijman, 2004; Bagshaw, Gray, & Snowden, 2014). In the current study, we carefully determined two important covariates — years since NCRMD verdict and intelligence. Previous research suggests that EF is an overlapping (e.g., Luciano et al., 2001; Carpenter, Just, & Shell, 1990; Miyake et al., 2001), but separate construct (e.g., Ardila, Pineda, & Rosselli, 2000; Damasio, 1994) from intelligence. Yearly review board decisions to determine whether forensic psychiatric patients receive discharge reflects patients’ behavior (e.g., violent or aggressive acts and in-custody rule infractions), severity of index offence, and criminal histories (Crocker, Nicholls, Charette, & Seto, 2014). Therefore, the number of years patients spent in custody (years since NCRMD status) was considered in the current study; however, the results of the current study showed that neither intelligence or number of years since NCRMD significantly added to the prediction of our outcome variables. Future research looking at EF and criminality should carefully consider the above listed factors.
Sample Size. The small sample size of both forensic psychiatric patients and criminal offenders limited the ability to detect effects smaller than d = .3; however, small sample sizes are common in forensics research due to difficulty accessing these populations and the small sample size. Future research should replicate this study with larger sample sizes.
Methodological Issues. The generalizability of this study is limited by sample characteristics. This research pertains to two specific criminal populations and suggests EF characteristics differ between criminal populations. Therefore, these results may not generalize across criminal offenders. It is also possible that individuals who volunteered to participate in this study were unique in some way (e.g., less disordered, more
motivated) compared to those who did not volunteer, which may bias the sample and underestimate the true effect in both populations. Patients who did not volunteer or who were not eligible may have had lower EF and higher aggression and violence; therefore, the results of the current study may be weaker than what would be seen in forensic psychiatric patients as a whole.
Furthermore, since our sample consisted of only men, these results may not generalize to female criminal offenders. The little research that looked at EF in aggressive females found conflicting results. While some research found a relationship between EF and aggression (Daoust, Loper, Magaletta, & Diamond, 2006; Giancola, Mezzich, & Tarter, 1998), others found no relationship (Komarovskaya, Loper, & Wamen, 2007). Therefore, future research should examine sex differences in EF and aggression.
4.7 Implications
Currently, EF measures are not used or validated for risk assessment and release decisions. Risk assessments and release decisions are far from perfect and have room to improve (Crocker, Nicholls, Charette, & Seto, 2014). Given the EF deficits displayed in criminal populations and the potential for EF to predict violence and aggression, further exploration about the utility of EF in predicting violence and aggression is warranted. EF measures are easy to use and objective, which makes them potentially useful in risk and release decisions. EF improvement through rehabilitation programs can be used to inform risk and release decisions.
This research provides some evidence that EF is an important component of violence, aggression, and functional disability in criminal populations. An important next step would be to determine the utility of targeting EF in rehabilitation programs. There is evidence that rehabilitation programs effectively improve EF (e.g., Wykes et al., 2011;
Rath, Simon, Langenbahn, Sherr, & Diller, 2003; Worthington, 2005). These programs have the potential to be adapted and implemented in a criminal setting. It is possible that interventions targeting EF in forensic psychiatric populations could result in decreased recidivism and better integration into the community following discharge.
4.8 Conclusion
This research is novel and contributes to the existing literature in several ways. Firstly, Chapter 2 further explicated the relationship between the different aspects of EF and criminality in an understudied and often ignored population of criminal offenders. Secondly, both manuscripts (Chapters 2 and 3) demonstrated that forensic psychiatric patients and correctional offenders display severe EF deficits compared to normative groups, consistent with research that suggests EF deficits are ubiquitous across offender populations. Finally, this study uniquely had access to the EF scores of two different criminal populations, which allowed for a direct comparison between forensic psychiatric patients and correctional offenders. This comparison is useful to determine unique
differences of EF functioning in two criminal populations. The results of this research suggest that there are important EF differences in criminal populations that need to be considered in future research.
Further, the results suggest that EF may be important in understanding the
complex and multifaceted underlying factors that contribute to violence and aggression in criminal populations. Therefore, special attention needs to be paid to rehabilitating EF in order to reduce future offences and effectively transition individuals back into the community. Given the immense social and economic impact of violence and crime, understanding the factors that contribute to violence and crime is of the upmost importance.
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Appendices