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MIT 9 670 - Face Recall Systems

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“Face Recall Systems”OverviewMotivationFace Recall SystemsLaboratory StudiesThe IdentikitIdentikitPhotofitSlide 9Slide 10Slide 11Relevance to Field ExperiencePsycholgical FactorsPsychological Factors“Face Recall Systems”Jennifer Shieh [email protected] Act010118/9696Aggravated Robbery001123/8515Aggravated Robbery000717/0730Overview•Motivation•Face Recall Systems- Identikit- Photofit- Minolta Montage Synthesizer- Strip systems- Sketch artists•Laboratory Studies•Psychological FactorsMotivation•Alphonse Bertillon and his portrait parlé–Designed to help detective retain info about known criminal–Also used as witness aid•Considerations–Difficulty generating good verbal descriptions, witness drawings–Economical and convenient–But, does it work well?Face Recall Systems•Break face down into component features•Operator assists witness in selecting components•Features integrated by a variety of techniques•Effectiveness? –Identikit: aid in clearing 5-10% cases (Venner, 1969)–Photofit: 25% “greatly assisted” cleared cases (Darnbrough, 1977)Identikit: line drawings printed on transparencies layer to get composite facePhotofit: photos of individual features fit in special frameMinolta Montage Synthesizer: library of mugshots optically blended compositeStrip systems: dissect face into series of horizontal strips that can be exchangedSketch artists: alternative to face-recall kit, traditional, complementary to kitsLaboratory Studies•Issues–Establish system accuracy limits (under controlled laboratory conditions)–Sensitivity to factors that normally influence accuracy(e.g. performance fluctuations due to effects of sex and race)–Correlations of successful performanceThe Identikit•Studies done by Laughery et al (1977)•Method–Pairs of subjects (witnesses) talked to target person for 7-8 min, informed of required recall–Witnesses constructed likenesses of target from memory, one with sketch artist and one with Identikit technician–Artist and technician constructed likeness with target present (optimum performance)–Panels of judges rated similarity of sketches & Identikits to photos of target; computerized search algorithm to detect target in a “mug file”–3 studies, 3 different types of targets: white males, white females, black malesIdentikit•Results–Significant overall advantage for sketches compared to Identikit•Neither method effective for computerized search–Sketches made w/ target present significantly better than those from memory, but no corresponding difference for Identikits in study with white targets–For study with black targets, both sketch and Identikits made from view had higher likeness ratings than those from memoryPhotofit•Studies –Encoding accuracy (Ellis et al, 1975)•In Photofit, construct white male face that was itself a Photofit composite, with composite in view or after 10-s observation.•Construct from photos of white males from memory–Effect of delay between observation and construction (Davies et al 1978)•Construct from photos of white males seen for 10 s from memory immediately after observation, one week later•Construct three weeks later; also, recognize Photofit face among 36 mugshots to provide measure of trace strength for face–Ability of Photofit to reflect fluctuations in trace strength and availability (Ellis)•Observe video of white male reading a passage; ½ attend to passage, ½ to face•Answer questions on passage and make Photofit impressionPhotofit–Sketches vs. Photofit (Ellis)•Witnesses sketched from photos; ½ w/ target in view, ½ from memory–Influence of sex and race of witness (Ellis)•Male and female witnesses constructed likenesses of male and female target from memory, 10-s observation of each target•White Scottish and black African students made Photofits from memory of one black and one white face, 15-s observationPhotofit•Results–Encoding accuracy•Low- no subject completed a face entirely correctly but accuracy higher when task was done from view than from memory–Effect of delay•Overall accuracy was low, but no effect was found for delay•While there was no effect for delay in construction of a Photofit, significant decline in recognition accuracy with a 3-week delay. Trace strength had great decline but this was not reflected in Photofit accuracy.–Fluctuations in trace strength and availability•Subjects attending to passage had higher test scores but Photofits made by face-oriented subjects were rated no better than those made by passage-oriented subjectsPhotofit–Sketches vs. Photofit•Photofits were no better when composed from view than from memory•With target face present, Photofits much lower than subjects’ own sketches•From memory, Photofits were marginally superior–Influence of Sex•No differences in accuracy due to either the sex of the target or the sex of the witness, despite sex effects normally found in face recognition studies–Influence of Race•Avg accuracy of composites of white targets almost 2x as high as for black•Differences in accuracy due to race of the witness were confined to composites of white targets•Despite usually reported effects of race, no effect found with composites of black targetsRelevance to Field Experience•Both Identikit and Photofit have low sensitivity, demonstrated by failure to show superiority when construction made in presence of target; also, do not show expected fluctuations in performance•However, both were capable of generating identifiable images, and, on occasion, showed expected sensitivity •But, how relevant are the experiments to field operation?–Effect of emotive context when trying to encode face during a crime–Adverse character traits attributed by witnesses to criminal, distort composite–Training of technicians–Nature of the accuracy criteria in laboratory studies- too high?Psycholgical Factors•Interference effects in face recall–Don’t appear to be any interference effects, maybe facilitation–Systems produce varying effects upon subsequent recognition, depending on style of operator (~verbal interrogation)•Mode of representation–Line-drawn systems: not very life-like appearance–Photo: interpret composite as specific individual, not approx. likeness; study showed higher ID rates for photos–More like a real face composite becomes, greater the probability of identification


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