Marijuana Impairs the Accuracy of Eyewitness Memory and the Confidence–Accuracy Relationship Too

Abstract

Many factors that affect eyewitness identification accuracy do not affect the accuracy of high-confidence identifications. This is critical because legal cases are more likely to be prosecuted if they involve high-confidence eyewitnesses. Using a confidence–accuracy characteristic (CAC) analysis, we tested whether marijuana affects eyewitness memory generally and the accuracy of high-confidence judgments specifically. Marijuana users (N = 114) were randomly assigned to a marijuana or control condition and participated in a face recognition memory test with confidence ratings. Marijuana reduced identification accuracy (Cohen's d = .47), and the proportion correct for positive identifications, even at high-confidence, was significantly lower in the marijuana than control condition. Furthermore, marijuana impaired metacognitive awareness more generally; control (but not marijuana) participants provided more high-confidence ratings to faces studied for 5 s than 1.5 s. All high-confidence identifications are not equally likely to be correct, and stoned eyewitnesses do not make good eyewitnesses.