Credible Testimony in and out of Court
Spellman, Barbara A., Tenney, Elizabeth R., Psychonomic Bulletin & Review
Assessing informants' credibility is critical to several aspects of the legal process (e.g., when police interrogate suspects or jurors evaluate witnesses). There is a large body of research-from various areas of psychology and allied fields-about how people evaluate each others' credibility. We review the literature on lie detection and interpersonal perception to demonstrate that inferences regarding credibility may be multiply determined. Specifically, characteristics of the informant, of the listener, and of the situation affect people's perceptions of informants' credibility. We conclude with a discussion of research on calibration (i.e., an informant's confidence-accuracy relation) because it offers fruitful avenues for future credibility research in the legal domain.
The quintessential courtroom scene-jurors listening intently to a lawyer questioning a witness-illustrates the importance of testimony to legal proceedings. Yet people's reliance on the testimony of others is pervasive in all sorts of everyday endeavors: We make decisions about what to do or what to buy on the basis of the advice (testimony) of others, and often, even our most basic knowledge- for example, that the earth is round-comes through the testimony of others.
What makes us choose to take the testimony of some people seriously (e.g., "there are weapons of mass destruction in Iraq") but seriously doubt the testimony of others (e.g., "this car was driven by a little old lady only to church on Sunday mornings")? Many factors affect such judgments-some consciously and some unconsciously-including characteristics of the speaker, of what the speaker said, of the listener, and of the situation.
Evaluating Credibility In and Out of Court
Many rules of evidence and courtroom procedures make it clear that it is important that the trier of fact (be it a judge or a jury) should have ample opportunity to assess the veracity of witnesses. These rules and procedures are based on things as disparate as the United States Constitution and folk psychology. Jurors almost always get to see and hear witnesses as they provide testimony. That procedure is reinforced by the defendant's Sixth Amendment right "to be confronted with the witnesses against him," but courts seem to have an independent belief in the importance of jurors being able to see and assess the demeanor of all witnesses in all cases when they are testifying, as a means of assessing their credibility. The ability to cross-examine a witness on the stand is also viewed as an important means for assessing credibility. Other evidence that can be presented to jurors to help them assess credibility includes conflicting testimony by other witnesses, prior inconsistent statements by the witness, information about the witness's past conviction of certain crimes deemed to be relevant to issues of credibility, and testimony regarding the witness's reputation for truthfulness.
Although most of the rules and procedures have been investigated to some extent, the issue of how people use their own observations of an informant's characteristics and presentation style to infer credibility has garnered a huge amount of attention in the psychology literature. We first review the literature on how characteristics of the informant, of the listener, and of the situation affect credibility. Then we turn to recent research on how people use information about an informant's calibration. Calibration requires the integration of two cues to credibility: confidence and accuracy. We believe that calibration is an important, useful, and understudied cue for assessing credibility.
Note that in many of the laboratory studies reviewed here, the informants were college students or other "regular" people who were instructed to lie (or tell the truth) about things like personal opinions or the contents of a picture that they could see but the observer could not. Typically, the informants are told to lie half the time, and the participants know that the informants will lie on half the trials. …