Spanos, N. P., Myers, B., DuBreuil, S. C., & Pawlak, A. E. (1992-1993). The effects of polygraph evidence and eyewitness testimony on the beliefs and decisions of mock jurors. Imagination, Cognition and Personality, 12, 103-113.
257 undergraduates serving as mock jurors heard 1 of 4 versions of a murder trial and then deliberated in small groups to a verdict. Half the juries heard a trial in which an eyewitness identified the defendant as the murderer and half heard a trial in which a polygraph expert testified that the defendant responded deceptively when denying the crime. These 2 factors were completely crossed in a 2 × 2 (eyewitness/no eyewitness × polygraph/no polygraph) design. Ss exposed to the eyewitness testimony believed more strongly in the defendant’s guilt and voted guilty more frequently than did those not exposed to eyewitness testimony. Eyewitness testimony also enhanced the degree to which Ss believed that other pieces of evidence indicated that the defendant was guilty. Strong impact of eyewitness testimony on jury verdicts; no impact of polygraph data. Conviction rate substantially higher for juries that heard eyewitness testimony compared with those that did not.