Rachel Searston

Model forensic science

This article provides an explanation of the duties and responsibilities owed by forensic practitioners (and other expert witnesses) when preparing for and presenting evidence in criminal proceedings. It is written in the shadow of reports by the National Academy of Sciences (US), the National Institute of Standards and Technology (US), the Scottish Fingerprint Inquiry and a recent publication entitled ‘How to cross-examine forensic scientists: A guide for Lawyers’. The article examines potential responses to questions focused on the need for scientific research, validation, uncertainties, limitations and error, contextual bias and the way expert opinions are expressed in reports and oral testimony. Responses and the discussion is developed around thematics such as disclosure, transparency, epistemic modesty and impartiality derived from modern admissibility and procedure rules, codes of conduct, ethical and professional responsibilities and employment contracts. The article explains why forensic practitioners must respond to the rules and expectations of adversarial legal institutions. Simultaneously, in line with accusatorial principles, it suggests that forensic practitioners employed by the state ought to conduct themselves as model forensic scientists.

Thinking forensics: cognitive science for forensic practitioners

Human factors and their implications for forensic science have attracted increasing levels of interest across criminal justice communities in recent years. Initial interest centred on cognitive biases, but has since expanded such that knowledge from psychology and cognitive science is slowly infiltrating forensic practices more broadly. This article highlights a series of important findings and insights of relevance to forensic practitioners. These include research on human perception, memory, context information, expertise, decision-making, communication, experience, verification, confidence, and feedback. The aim of this article is to sensitise forensic practitioners (and lawyers and judges) to a range of potentially significant issues, and encourage them to engage with research in these domains so that they may adapt procedures to improve performance, mitigate risks and reduce errors. Doing so will reduce the divide between forensic practitioners and research scientists as well as improve the value and utility of forensic science evidence.

The style of a stranger: identification expertise generalizes to coarser level categories

Experience identifying visual objects and categories improves generalization within the same class (e.g., discriminating bird species improves transfer to new bird species), but does such perceptual expertise transfer to coarser category judgments? We tested whether fingerprint experts, who spend their days comparing pairs of prints and judging whether they were left by the same finger or two different fingers, can generalize their finger discrimination expertise to people more broadly. That is, can these experts identify prints from Jones’s right thumb and prints from Jones’s right index finger as instances of the same “Jones” category? Novices and experts were both sensitive to the style of a stranger’s prints; despite lower levels of confidence, experts were significantly more sensitive to this style than novices. This expert advantage persisted even when we reduced the number of exemplars provided. Our results demonstrate that perceptual expertise can be flexible to upwards shifts in the level of specificity, suggesting a dynamic memory retrieval process.

Expertise with unfamiliar objects is flexible to changes in task but not changes in class

Perceptual expertise is notoriously specific and bound by familiarity; generalizing to novel or unfamiliar images, objects, identities, and categories often comes at some cost to performance. In forensic and security settings, however, examiners are faced with the task of discriminating unfamiliar images of unfamiliar objects within their general domain of expertise (e.g., fingerprints, faces, or firearms). The job of a fingerprint expert, for instance, is to decide whether two unfamiliar fingerprint images were left by the same unfamiliar finger (e.g., Smith’s left thumb), or two different unfamiliar fingers (e.g., Smith and Jones’s left thumb). Little is known about the limits of this kind of perceptual expertise. Here, we examine fingerprint experts’ and novices’ ability to distinguish fingerprints compared to inverted faces in two different tasks. Inverted face images serve as an ideal comparison because they vary naturally between and within identities, as do fingerprints, and people tend to be less accurate or more novice-like at distinguishing faces when they are presented in an inverted or unfamiliar orientation. In Experiment 1, fingerprint experts outperformed novices in locating categorical fingerprint outliers (i.e., a loop pattern in an array of whorls), but not inverted face outliers (i.e., an inverted male face in an array of inverted female faces). In Experiment 2, fingerprint experts were more accurate than novices at discriminating matching and mismatching fingerprints that were presented very briefly, but not so for inverted faces. Our data show that perceptual expertise with fingerprints can be flexible to changing task demands, but there can also be abrupt limits: fingerprint expertise did not generalize to an unfamiliar class of stimuli. We interpret these findings as evidence that perceptual expertise with unfamiliar objects is highly constrained by one’s experience.

Understanding expertise and non-analytic cognition in fingerprint discriminations made by humans

As a novice in a particular domain, thecognitive feats that experts are capable ofperformingseemimpressive,evenextraor-dinary. According to the well-establishedexemplar theory of categorization (e.g.,Brooks, 1987; Medin and Ross, 1989), anew category member in everyday clas-sification (e.g., a bird, a table, or a car)or expert classification (e.g., an abnor-mal chest x-ray, a patient with myocardialischaemia, or a poor chess move) is cat-egorized on the basis of its similarity toindividual prior cases. Often this sensitiv-ity develops effortlessly and without anyintention to learn similarities or differ-ences among the exemplars.Experts can do a lot with a little. Acrossvariousdomainsofexpertise,itseemsthatexperts can perform quickly and accu-rately when given only a small amountof information, as in chess (Gobet andCharness, 2006); fireground command(Klein, 1998); radiology (Myles-Worsleyet al., 1988; Evans et al., 2013), and der-matology(Normanetal.,1989).Theexpe-riential knowledge based on the hundredsof thousands of prior instances serves as arich source of analogies to permit efficientproblem solving.A fruitful approach to understand-ing these cognitive feats has been tounderstand where expertise lies in var-ious domains. Expertise in ball sports,for example, seems to lie in anticipatingwhere the ball will be (Abernethy, 1991);expertise in wine seems to lie in apply-ing verbal labels (Hughson and Boakes,2001); expertise in radiology seems to liein rapid discrimination of normal andabnormalradiographs(Evansetal.,2013);and expertise in chess seems lie in rapidretrieval of board configurations frommemory (Chase and Simon, 1973).Over the last several years, we havebeen working with a fascinating groupof experts who spend several hours aday examining a highly structured set ofimpressions. When a fingerprint is foundat a crime scene it is a human exam-iner, not a machine, who is faced withthe task of identifying the person wholeft it. Professional fingerprint examin-ers are usually sworn police officers whouse image enhancement tools, such asPhotoshop or a physical magnifying glass,and database tools to provide a list ofpossible matching candidates. They placea crime scene print and a suspect printside-by-side—physically or on a computerscreen—andvisuallycomparetheprintstojudge whether the prints came from thesame person or two different people.These fingerprint examiners have tes-tified in court for over one hundredyears, but there have been few experi-ments directly investigating the extent towhich experts can correctly match fin-gerprints to one another, how competentandproficientfingerprintexpertsare,howexaminersmaketheirdecisions,orthefac-tors that affect performance (Loftus andCole, 2004; Saks and Koehler, 2005; Vokeyet al., 2009; Spinney, 2010b; Thompsonet al., 2013a). Indeed, many examinershave even claimed that fingerprint iden-tification is infallible (Federal Bureau ofInvestigation, 1984). Academics, judges,scientists, and US Senators have reportedon the absence of solid scientific prac-tices in the forensic sciences. They high-lighttheabsenceofexperimentsonhumanexpertise in forensic pattern matching,suggesting that faulty analyses may becontributing to wrongful convictions ofinnocent people (Edwards, 2009; NationalResearch Council, 2009; Campbell, 2011;Carle, 2011; Expert Working Group onHuman Factors in Latent Print Analysis,2012; Maxmen, 2012), and they lamentthe lack of a research culture in the foren-sic sciences (Mnookin et al., 2011). Thefield of forensics is, however, beginning toacknowledge the central role that falliblehumans play in the identification process(Tangen, 2013).Our first point of inquiry was to seewhether qualified, court practicing finger-print examiners are any more accuratethan the person on the street, and to get afeelforthekindsoferrorsexaminersmake.In our first experiment (Tangen et al.,2011), we tested the matching accuracyof fingerprint examiners from Australianstateandfederallawenforcementagencies.In a signal detection paradigm, we cre-ated ground-truth matching prints for useas targets, and highly-similar, nonmatch-ing prints from a national database searchfor use as distractors. We found that qual-ified, court-practicing fingerprint expertswere exceedingly accurate compared withnovices. Experts tended to err on the sideof caution by making more errors of thesort that could allow a guilty person toescape detection than errors of the sortthat could falsely incriminate an inno-cent person. A similar experiment, withparticipants from the US Federal Bureauof Investigation, produced similar results(Uleryetal.,2011),andafollow-upexper-iment found variability in the consistencywithin and between examiners’ decisions(Ulery et al., 2012). An examiner’s exper-tise seems to lie, not in matching prints

A visual familiarity account of evidence for orthographic processing in pigeons (Columbia livia) : a reply to Scarf, Corballis, Güntürkün, and Colombo (2017)

AbstractScarf et al. (Proc Natl Acad Sci 113(40):11272–11276, 2016) demonstrated that pigeons, as with baboons (Grainger et al. in Science 336(6078):245–248, 2012; Ziegler in Psychol Sci. https://doi.org/10.1177/0956797612474322, 2013), can be trained to display several behavioural hallmarks of human orthographic processing. But, Vokey and Jamieson (Psychol Sci 25(4):991–996, 2014) demonstrated that a standard, autoassociative neural network model of memory applied to pixel maps of the words and nonwords reproduces all of those results. In a subsequent report, Scarf et al. (Anim Cognit 20(5):999–1002, 2017) demonstrated that pigeons can reproduce one more marker of human orthographic processing: the ability to discriminate visually presented four-letter words from their mirror-reversed counterparts (e.g. “LEFT” vs. “ ”). The current report shows that the model of Vokey and Jamieson (2014) reproduces the results of Scarf et al. (2017) and reinforces the original argument: the recent results thought to support a conclusion of orthographic processing in pigeons and baboons are consistent with but do not force that conclusion.

Training perceptual experts: Feedback, labels, and contrasts.

Are strategies for learning in education effective for learning in applied visual domains, such as fingerprint identification? We compare the effect of practice with immediate corrective feedback (feedback training), generating labels for features of matching and mismatching fingerprints (labels training), and contrasting matching and mismatching fingerprints (contrast training). We benchmark these strategies against a baseline of regular practice discriminating fingerprints. We found that all 3 training protocols—feedback, labels, and contrasts—resulted in a significantly greater ability to discriminate new pairs of prints (independent of response bias) than the baseline training protocol. We also found that feedback and labels training produced significantly lower rates of bias (i.e., learners in these groups were less likely to overcall matches) compared with baseline training. Our results demonstrate 3 different ways to boost expertise with matching prints, and have direct application to training perceptual expertise. Les stratégies d’apprentissage utilisées en éducation sont-elles aussi efficaces pour l’apprentissage de domaines visuels appliqués, comme l’identification d’empreintes digitales? Nous évaluons l’effet de la pratique par rapport à la rétroaction corrective immédiate (formation sur la rétroaction), à la génération d’étiquettes relatives à des caractéristiques d’empreintes digitales appariées et non appariées (formation sur l’étiquetage) et à la comparaison entre des empreintes digitales appariées et non appariées (formation sur la comparaison). Nous comparons ces stratégies à des pratiques régulières de discrimination d’empreintes digitales. Nous avons constaté que les trois protocoles de formation – rétroaction, étiquettes et comparaison – ont entraîné une plus grande habileté à discriminer les nouvelles paires d’empreintes (indépendamment du biais méthodologique) par rapport au protocole de formation de base. Nous avons également constaté que les formations basées sur la rétroaction et sur les étiquetage produisaient des taux de biais considérablement inférieurs (par ex., les apprenants de ces groupes étaient moins susceptibles de manquer les paires appariées) par rapport aux formations de base. Nos résultats présentent trois différentes façons de renforcer l’expertise en matière d’appariement d’empreintes digitales et ont une application directe sur la formation de l’expertise perceptuelle.