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|eTheses from Faculty of Natural Sciences legacy departments
|Improving composite images of faces produced by eyewitnesses
Hancock, Peter J B
|University of Stirling
|When a witness views a crime, they are often asked to construct a facial likeness, or composite of the suspect. These composites are then used to stimulate recognition from someone who is familiar with the suspect. Facial composites are commonly used in large scale cases e. g. Jill Dando, Yorkshire Ripper, however a great deal of research has indicated that facial composites perform poorly and often do not portray an accurate likeness of the suspect. This thesis therefore examined methods of improving facial composites. In particular, it examined methods of increasing the likeness portrayed in composites, both during construction and at test. Experiments 1 to 3 examined the effectiveness of a new three-quarter-view database in PROfit. Experiment 1 examined whether the presentation of composites in a three-quarter- view composite will aid construction. Participant-witnesses were exposed to all views of a target and the results indicated that three-quarter-view composites performed as well as full-face composites but not better. Experiments 2 and 3 then examined whether the presentation of two composites (one in a full-face view and the other in a three-quarter-view) from the same participant-witness would increase performance above the level observed for a single composite. The results revealed that two views were better than one. In addition, experiment 3 examined the issue of encoding specificity and viewpoint dependency in composite construction. All participant-witnesses were exposed to either one view of a target (full-face or three-quarter) or all views and they were asked to construct both a full-face and a three-quarter- view composite. The results indicated that performance was better when all views of a face had been presented. When a target had been seen in a three-quarter-view, it was better to construct a three-quarter-view composite. However, when a target had been seen in a full-face view, performance for both full-face and three-quarter composites was poor. Experiments 4 to 8 examined whether the presentation of composites from multiple witnesses would increase performance. The results revealed that morphing composites from four different witnesses (4-Morphs) resulted in an image that performed as well as or better than the best single image. Further experimentation attempted to examine why multiple composites performed well. In particular, it was asked whether multiple composites performed well because they contained varied information or whether they performed well because they just contained more information. Multiple composites from both single and multiple witnesses using the same (PROfit) and different (PROfit, E-FIT, Sketch, EvoFIT) composite techniques were compared and the results revealed that multiple composites performed well because they contained different memorial representations. This combination of different memorial representations appeared to result in an image that was closer to the ideal, or prototypical image. Experiments 9 to 12 examined the relationship between verbal descriptions and composite quality. The results revealed that there was no clear relationship between the amount of description provided, the accuracy of the description and performance of the resulting composite. Further experimentation examined whether the presentation of a composite and a description would increase performance above the level observed for a single composite. The results revealed that the combination of a description and a composite from the same participant-witness did increase performance. This indicated that descriptions and composites might contain differing amounts and types of featural and configurational information. Both the theoretical and practical implications of these results are discussed. Experiments 1, 2 and 3 of this thesis have been submitted for publication. Ness, H., Hancock, P. J. B., Bowie, L. and Bruce, V. Are two views better than one? A study investigating recognition of full-face and three-quarter-view composites. Applied Cognitive Psychology. Experiment 4 of this thesis appears in Bruce, V., Ness, H., Hancock, P. J. B., Newman, C. and Rarity, J. (2002). Four heads are better than one: combining face composites results yields improvements in face likeness. Journal of Applied Psychology. 87 (5), 894-902. Other Publications Frowd, C. D., Carson, D., Ness, H., Richardson, J., Morrison, L., McLanaghan, S., Hancock, P. J. B. Evaluating Facial Composite Systems. Manuscript accepted for publication in Psychology, Crime and Law. Frowd, C. D., Carson, D., Ness, H., McQuiston, D., Richardson, J., Baldwin, H., Hancock, P. J. B. Contemporary Composite Techniques: The impact of a forensically relevant target delay. Manuscript accepted for publication in Legal and Criminological Psychology.
|Thesis or Dissertation
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