No evidence for neuroscience bias in adult or juvenile cases: A pre-registered mock juror study

Objectives: Previous studies reported an over-persuasiveness effect of neuroscientific results when compared to behavioral results in adult cases. This concern needs to be addressed carefully, given that the evidence for neuroscience bias is mixed and that juvenile cases are different from adult cases. We conducted mock jury studies to examine the neuroscience bias in juvenile cases. Hypotheses: There is no neuroscience bias in juvenile cases. Methods: We conducted two mock jury studies with a three (evidence type: behavioral evidence, neuroscience evidence without brain images, and neuroscience evidence with brain images) by two (offenders’ age: juvenile vs. adult) between-subject design. In a pilot study (n = 94) and a pre-registered study (n = 324), participants read a vignette describing an appeal case where the defendant’s lawyer introduced scientific evidence, then made a series of judgments, including the death penalty and criminal responsibility of the defendant. Results: In the pre-registered study, a one-way ANOVA on the effect of evidence type in juvenile conditions did not find evidence for a main effect of evidence type, F(2, 150) = 0.31, p = .73, ηG2 = .004, BF10 = 0.09. In adult conditions, there was no main effect of evidence type either, F(2, 168) = 0.31, p = .33, ηG2 = .013, BF10 = 0.16. The critical analysis revealed the same pattern in the criminal responsibility of the defendant. We found evidence for the non-existence of the effect of evidence type in juvenile condition, F(2, 150) = 0.71, p = .49, ηG2 = .009, BF10 = 0.12, in adult conditions, F(2, 168) = 0.49, p = .61, ηG2 = .006, BF10 = 0.09. Conclusions: Our registered study suggests that neuroscientific evidence is not more persuasive than behavioral evidence, in either adult or juvenile cases. These results call for an end to the debate on neuroscience bias.