Latent print examinations involve a complex set of psychological and cognitive processes. This article summarizes existing work that has addressed how training and experience creates changes in latent print examiners. Experience appears to improve overall accuracy, increase visual working memory, and lead to configural processing of upright fingerprints. Experts also demonstrate a narrower visual filter and, as a group, tend to show greater consistency when viewing ink prints. These findings address recent criticisms of latent print evidence, but many open questions still exist. Cognitive scientists are well positioned to conduct studies that will improve the training and practices of latent print examiners, and suggestions for becoming involved in fingerprint research are provided.
Latent print examiners face a daunting task. Fingerprints are often the only physical evidence left at a crime scene, but these are typically invisible until developed and lifted. Even after they are dusted with lifting powder and stabilized using clear lifting tape or fixed using cyanoacrylate fumes, friction ridge impressions may be corrupted by visual noise or may have missing regions. In some cases, it may even be difficult to orient the print correctly. This impression of the print must then be compared against a known standard, which can be either an ink print of a suspect developed by the investigating detective or one provided by a donor who has previously entered into the criminal justice system, whose prints now reside in a computerized database.
Although computers are used to store databases of fingerprints and to suggest possible matches, the amount of distortion and noise in latent prints prevents computer algorithms from performing near the level of human examiners. Thus, virtually all evidence admitted in courts comes from the testimony of experts. It is up to the examiners to decide whether they believe that there exists sufficient evidence to conclude that the two impressions (the latent and the ink print) come from the same source or that it can be excluded that they come from the same source.
The decision itself is fraught with complications. To conclude that the two impressions come from the same source implies that one has compared the latent print with all possible donors, which could be interpreted as all people who were in a position to leave the impression at the particular location. This set is potentially quite large, making any conclusion about individuality quite problematic. The flip side of this argument is that fingerprints are unique (as are all patterns in nature) and even identical twins have differentiable friction ridge impressions (Jain, Prabhakar, & Pankanti, 2002).
Latent print examiners are caught between these two philosophical extremes, and given that skin may change through scars or wear, many practitioners now favor the term persistence over uniqueness. The field has had to contend with a steady stream of criticism, most recently from a National Research Council of the National Academy of Sciences (2009) report that highlighted what the panel saw as serious deficiencies in the practices of forensic scientists. However, even the most ardent critics of fingerprint identification would likely agree that there is some value in latent prints, and the aim of criticism is to address some of the shortcomings of current approaches.
Cognitive scientists have a role to play in this process, and the goal of this article is to discuss some of the major issues confronting the applied science of latent print examinations. We will review some of the nascent research on expertise among latent print examiners, as well as related research from cognitive psychology. This article focuses on the perceptual expertise side of latent print examinations; a companion article in this special issue by Dror and Cole (2010) addresses the cognitive biases that can affect the decision process, among other issues. …