Do Multiple Doses of Feedback Have Cumulative Effects on Eyewitness Confidence?

We tested whether multiple doses of feedback have cumulative effects on eyewitness-identification confidence. In Experiment 1, participants made mistaken identifications and received or did not receive three forms of confirming feedback: (1) co-witness feedback; (2) vague feedback from the experimenter (“You've been a good witness”); and (3) inference-based feedback, in which eyewitnesses were led to infer that their identification was accurate. Co-witness feedback and inference-based feedback independently inflated eyewitness confidence, providing some evidence of cumulation. In Experiment 2, participants received or did not receive co-witness feedback and/or inference-based feedback following their mistaken lineup identifications. Two doses of feedback produced significantly higher confidence than did one dose of feedback, demonstrating significant cumulation. These findings suggest that multiple doses of subtle post-identification feedback can cumulate to have large distorting effects on later testimony.