Abstract
Aim of the StudyThe study examines how neurobiological and genetic explanations of psychopathy influence decision-making of German law students about legal and moral responsibility and sentencing of a defendant in a case of manslaughter. Previous studies from the United States and Germany have been criticized because they partly contradict legal analyses of real-world criminal cases. With a modified design, which integrates the main criticism, we re-examined the impact of biological explanations for psychopathy on decision-making in the courtroom.MethodsWe developed an improved quasi-experimental design to probe three case vignettes presenting different explanations of psychopathy in a criminal case of manslaughter. All three vignettes present the same information about a forensic expert’s testimony that is said to report compelling evidence for the diagnosis of “psychopathy.” The independent variable being manipulated is the type of information supporting the expert diagnosis: either no biological explanation of “psychopathy” versus a neurological explanation (brain injury) versus a genetic explanation (MAOA gene). The outcome measure is a questionnaire on legal and moral responsibility, free will, the type of custody, and the duration of the sentence. The study is adequately powered. We openly publish the data and all statistical analyses as reproducible R scripts.ResultsThe answers of German law students (n = 317) indicate that the omission of a neurobiological explanation is significantly associated with higher ratings of legal responsibility while compared to no biological explanation. However, there was no significant difference on the prison sentencing and type of custody assigned. Furthermore, there was no difference in the self-reported impact of the explanation of psychopathy on the participants’ decision-making.ConclusionOur findings from German law students corroborates previous research on German judges but is markedly distinct from studies on United States judges. Whereas in the United States, biological information seems to have a mitigating effect, it seems to increase the rate of involuntary commitment to forensic psychiatric hospitals in Germany.
Highlights
Both United States courts and commentators have discussed the use of neuroscientific and genetic evidence in criminal cases as a “double-edged sword” for the defendant (Denno, 2012)
We suggest that the question whether neuroscientific and genetic evidence in criminal cases is a double-edged sword cannot be answered in general
The main purpose of this research was to understand the judgments of German law students depending on two different types of neuroscientific evidence being presented in the courtroom
Summary
Both United States courts and commentators have discussed the use of neuroscientific and genetic evidence in criminal cases as a “double-edged sword” for the defendant (Denno, 2012). Neuroscience and genetic evidence is increasingly being introduced in criminal cases in the United States (Denno, 2012, 2015; Denno and McGivney, 2013; Farahany, 2015), in Canada (Chandler, 2015), Western Europe (Catley and Claydon, 2015; De Kogel and Westgeest, 2015), and Australia (Alimardani and Chin, 2018). In most of these cases, clinically established techniques such as EEG, structural brain imaging, and positron emission tomography have been used to demonstrate brain damage, whereas fMRI and neurogenetics have been used only in few cases (Fuss, 2016)
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