Marijuana impairs the accuracy of eyewitness memory and the confidence–accuracy relationship too.
Kathy Pezdek, Erica Abed, Daniel Reisberg
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.