Visual and other demonstrative evidence has become increasingly prevalent in American and other courtrooms in recent years. However, there have been relatively few experimental studies of the effects of this kind of evidence in legal settings. As a consequence, little is known about when and how it affects legal decision making. In this article, I survey the extant research, including studies of photographs, videos, computer animations, and PowerPoint displays. The research shows that visual evidence affects legal decisions in some circumstances but not in others. It also indicates that visual evidence sometimes enhances legal judgment by improving recall and understanding but sometimes impairs judgment by prompting undue emotional responses, cognitive and perceptual biases, and/or peripheral processing. The limitations of the research are discussed, and directions for future research are suggested.
Visual and other demonstrative evidence, including photographs, drawings, maps, and models, has long been used in court to illustrate the oral testimony of eyewitnesses and experts (Mnookin, 1998).1 It has become increasingly prevalent in recent years, in large part because digital technology has made it easier to record or, in the case of computer animations, to recreate legally relevant reality visually (Feigenson & Spiesel, 2009). A dashboard camera video, for instance, provided the dispositive evidence in a recent Supreme Court decision on the police's authority to use deadly force to terminate a car chase (Scott v. Harris, 2007),2 and a cell phone video will be critical should a lawsuit brought against a New York City police officer for assaulting a bicyclist proceed to trial (Weichselbaum, 2009).3
Although there have been efforts to document courtroom technology generally (e.g., Center for Legal and Court Technology, 2007) and to instruct judges and lawyers in its use (e.g., Federal Judicial Center/National Institute for Trial Advocacy, 2001), there have been relatively few experimental studies of the effects of visual and multimedia evidence in legal settings. As a consequence, little is known about when and how this kind of evidence affects legal decision making. A better understanding should be not only of intrinsic interest to cognitive psychologists but also extremely useful to the legal system, helping policy makers and judges to regulate the use of such evidence more wisely and informing advocates as they decide when and how to present it.
VARIETIES OF VISUAL EVIDENCE
There are good reasons to suspect that visual evidence may influence ultimate judgments of guilt or liability and damages. The police officers who beat Rodney King might never have been brought to trial were it not for George Holliday's videotape of the incident, and the jurors' verdict arguably turned on their interpretations of the tape. As surveillance videos made by both governments and private citizens proliferate, such evidence is likely to make a difference in more and more cases (see Feigenson & Spiesel, 2009). Even where it is not necessarily the focal point of the case, visual evidence would likely influence decision makers' thoughts and feelings and, hence, their verdicts. Because still or moving pictures can be more vivid than oral testimony or text, for instance, visual evidence could well be more memorable and/or lead to stronger emotional responses (see Bell & Loftus, 1985), either of which could affect the outcome. Personal injury lawyers often present day-in-the-life movies of an accident or malpractice victim (e.g., Joseph, 1997), presumably because they believe that the movies give jurors a better understanding of the extent of the victim's injuries and/ or encourage them to sympathize with the victim, leading to larger damage awards. In short, general cognitive psychological research, the practices of experienced trial lawyers, and perhaps common sense all suggest that visual evidence may often affect legal outcomes. …