The limited effect of electroencephalography memory recognition evidence on assessments of defendant credibility

Abstract

The admissibility of neuroscientific evidence is becoming an increasingly important issue for American courts. Scholars have suggested that in the context of neuroscientific evidence generally, and brain evidence related to deception in particular, Rule 403 concerns may be particularly salient. Yet despite concerns under Rule 403 about the prejudicial effects of neuroscientific evidence, the scholarly empirical literature on the effects of such evidence is decidedly mixed. This article reports on new results from a study examining the effect of neuroscientific evidence on subjects’ evaluation of a fictional criminal fact pattern, while manipulating the strength of the non-neuroscientific evidence. By manipulating the strength of the case, we are able to estimate the marginal effect of introducing neuroscientific evidence. We do this in the context of brain-based memory recognition with electroencephalography (EEG) evidence. In two experiments, one using 868 online subjects and one using 611 in-person subjects, we asked subjects to read two short, fictional vignettes describing a protagonist accused of a crime. We manipulated (i) the expert evidence (none, incriminating brain evidence, exculpating brain evidence, incriminating polygraph evidence, and exculpating polygraph evidence), and (ii) the strength of the non-neuroscientific facts against the defendant (weak facts with an alibi, medium facts, and strong facts with a motive). We found that although there is a statistically significant relationship between exposure to neuroscientific information and subjects’ evaluations of the fictional defendant, the neuroscientific evidence was not as powerful a predictor as the overall strength of the case in determining outcomes. Our primary conclusion is that subjects are cognizant of, but not seduced by, brain-based memory recognition evidence. Subjects consider the evidence, and it has an effect in some contexts on their evaluations, but they generally weigh it as just one of many facts on the record.