Presentation on theme: "Eyewitness testimony and its limitations. Why is eyewitness testimony so error-prone? 1. Poor view of events and their perpetrators. 2. May not appreciate."— Presentation transcript:
Eyewitness testimony and its limitations
Why is eyewitness testimony so error-prone? 1. Poor view of events and their perpetrators. 2. May not appreciate events’ significance at the time (e.g., con-man). 3. Changes in the suspect's appearance (e.g. disguises). 3. Effects of witnesses’ stress/arousal: “weapon focus” (e.g. Christianson and Loftus 1991). 4. Elapsed time since event was witnessed. 5. Effects of post-event information (e.g., witnesses’ own ruminations; listening to other people's accounts of it; misinformation). 6. Effects of expectations and schemas (both on initial encoding and subsequent memory). 7. Weak relationship between witnesses' accuracy and confidence.
Wells and Olson (2003): Review factors affecting eyewitness performance. System variables - under control of legal system (e.g. interview procedures, lineup presentation modes, etc.) Estimator variables - not under control of legal system (e.g. sex and age of witnesses, lighting conditions at time of crime, etc.) Little evidence of effects of witness' sex and intelligence. Effects of age, event duration, stress/arousal, cross- race identifications.
Exposure time and delay: MacLin, MacLin and Malpass (2001): Review. Increased exposure time usually improves recognition accuracy, reduces false identifications. Increased delay usually decreases recognition performance, increases false identifications. Delay has little effect on familiar face recognition (e.g. schoolmates, Bahrick, Bahrick and Wittlinger 1975). Loftus, Schooler, Boone and Kline (1987): People overestimate duration of events, especially when stressed. Read (1995): Increased exposure time can decrease performance by increasing witnesses' readiness to make false identifications (confuse increased familiarity due to contextual information, with increased familiarity from perceptual knowledge).
Effects of expectations and schemas: Allport and Postman (1947): Picture of a black man, and a white man holding knife. Participants tended to recall that it was the black man holding the knife. Bartlett (1932): "War of the Ghosts" - memory distortions stem from attempts to make sense of events, relate them to known facts, beliefs, etc. Neisser (1981): James Dean and Watergate testimony: memory for gist, but inaccurate about temporal order of events, who said what to whom, precisely what was said, etc.
Effects of stress and arousal: Yerkes-Dodson "Law" (1908): inverted U-shaped relationship between stress/arousal and performance. Easterbrook (1959): cue utilisation hypothesis: stress narrows attention to central items at expense of peripheral ones. Steblay (1992): "Weapon focus" effect: decreased recognition due to presence of a weapon. Christianson (1992): effects of stress are an interaction between stress level and many other factors.
Peters (1988): Effects of stress on face recognition. Memory for face of nurse and aide during immunisation. Pulse rate higher for nurse than aide. Aide identified better than nurse, from target-present lineup. Yuille and Cutshall (1986): Naturalistic study of recall by 13 witnesses of a violent crime. Their reports analysed for accuracy and also compared with earlier police reports. Accurate memories for events 4-5 months later. Reported stress level at time of crime not significantly related to subsequent recall. But higher-stress witnesses also closer and more involved in the crime.
Loftus, Loftus and Messo (1987): Subjects saw one of two filmed versions of an event in a restaurant. Version A: a man pointed a gun at a cashier and she handed him money. Version B: the man gave her a cheque and she gave him money. Recorded eye-movements: version A subjects fixated on the weapon more than version B subjects; also showed poorer recall of other details and were less able to identify the robber from a photo array. Loftus and Burns (1982): Violent and non-violent films of a "crime". Subjects in violent version were less able to recall details of the event. Memory impaired for details immediately preceding the violent scene, and for details occurring up to 2 mins earlier. Valentine and Mesout (2009): Effects of stress on memory for an actor in the London Dungeon. High stress: 17% recognised him. Low stress: 75% recognised him.
Steblay (1992): Meta-analysis of studies on "weapon focus". Fairly reliable effect. Pickel (1999): Novelty can produce similar effects.
Effects of post-event misinformation: Loftus, Miller ands Burns (1978): Confusion between originally-witnessed event and information from post-event questions.
Influences of witnesses on each other: Memon and Wright (1999): 1995 Oklahoma bombing and hunt for "John Doe". Wright, Self and Justice (2000): Pairs were unaware they had seen different versions of a storybook (present or absent "accomplice" to a crime). Discussion produced conformity in pairs' responses. Gabbert, Memon and Bull (2003): Pairs saw different videos of a "theft". 60% of those who had not seen the crime came to believe it had occurred; 30% who had seen it came to believe it had not occurred.
Cross-race identification (own-race bias): Meissner and Brigham (2001): Meta-analysis of 39 studies, over 30 years. Affects recognition, lineups, RT studies, Photofits, etc. Over twice as likely to identify own-race than other-race. Less hits, more false alarms with other-race faces than with own- race faces. False alarms worse with short exposure times, and long delays between study and test. ORB accounts for 15% of variance in discrimination accuracy. Robust finding, but reasons for it are unclear.
Sporer (2001b): Two aspects to ORB: (a) impaired recognition (b) shift in response bias (increased false positives, due to increased readiness to say "seen before"). ORB generally strongest for Whites recognising other races - occurs with many different races. Sporer (2001a): Review of non-laboratory studies of ORB. Archival studies in Britain and Germany suggest non-Whites and non-German suspects are more likely to be identified in lineups. Field studies (photospread of experimenters posing as shop "customers") show ORB.
Explanations for Own-Race Bias (ORB): Prejudice: Only indirectly, by reducing contact with other races. Physiognomic variability: Little evidence for this (Goldstein and Chance 1979). Inter-racial contact: Most studies find increased contact reduces ORB (e.g. black South Africans: Wright, Boyd and Tredoux 2003). May do this by perceptual learning (differentiation by focusing on task-relevant facial aspects).
Sporer (2001b): In-group/out-group model of face processing. 1. In-group face - automatic configural processing. 2. Out-group - face categorisation occurs, and step 1 is bypassed.
Face-space models and perceptual expertise: Valentine (1991): Other-race faces are encoded in Multi-Dimensional Face Space with respect to inappropriate own-race norms. Exemplar-based modelVector-based model
Sporer (2001b): 5 factors influence identifying an other-race face: 1. Attentional processes at encoding: may be influenced by social disregard cues or categorization processes (which may lead to inadequate processing). 2. Perceptual expertise (related to contact). 3. Distinctiveness of target relative to other people in that ethinic group: may not be apparent to out-group witness. 4. Difficulty of task, affected by inter-item similarity and fairness of a lineup (constructed by out-group member). 5. Social factors, e.g. witness' motivation to make a positive identification, biased lineup instructions, police officers' expectations.
MacLin and Malpass (2001): "Ambiguous race face effect". Hispanic participants who saw composites with "hispanic" hair recognised them better than hispanic participants who saw same composites but with "black" hair. Bernstein, Young and Hugenberg (2007): Image background colour affected face recognition if participants thought it signified in-group/out-group membership.
Motivational factors in other-race effect? " Own gender" bias (Wright and Sladden 2003). "Own-age" bias (Wright and Stroud 2002; Anastasi and Rhodes 2006; Perfect and Moon 2005). Harrison and Hole (2009): Trainee teachers better than other students at recognising children's faces. Difficult to explain by perceptual expertise OR Sporer's model. Motivation? Expertise promoted by need to differentiate exemplars? Also explains Wright, Boyd and Tredoux's (2003) ORB results.
Conclusions: Numerous factors affect eyewitness performance at encoding, storage and retrieval phases. Encoding affected by stress, although difficult to investigate experimentally. Retrieval affected by operation of standard memory effects (schemas, trace decay, interference, etc.) plus social factors (demand characteristics, influence of questioner and other witnesses). Exacerbated by ORB in cases involving cross-race identification.