Understanding and Improving the Effectiveness of Sketch Facial Composites

Abstract

Constructing a facial composite sketch by a forensic artist is one of the oldest, yet least researched methods of facilitating an eyewitness’s memory for an offender’s face and depicting it based on their recall and instructions. While a lot is known about how faces are processed in relation to computerised composites systems such as E-FIT and newer holistic systems, little is known of the mechanisms of sketch composites and their effectiveness. There are two main ways of constructing a sketch composite; by using reference materials (e.g., pictures of facial features or hairstyles) as recognition aids to support recall or not using them and for the witness to rely on the developing sketch as a comparison point for their mental image of the face. How long an offender is seen is one of the key factors in the storage and retrieval of the memory of them and it is important to explore the role of reference materials (or not) when encoding duration has been short or longer. Experiments 1, 2 and 3 examined these two factors in a 2 x 2 study design. Overall, it was found that longer encoding (30 sec – 60 sec) led to more effective composites (resembled the target better/were more identifiable) than short encoding (5 sec). No overall benefit for the use of reference materials was found, however, it is indicated that they improve the composites after short encoding. Recall is a vital part in sketch composite construction, which can be enhanced in a composite interview with specific mnemonics and instructions. One of the most effective ones is mentally reinstating the context of the situation where encoding of the offender occurred by thinking about any cues from the environment, sounds, smells and one’s emotions and moods. A more detailed version of this is to also verbally describe it to the interviewer, which has been found to be effective with computerised systems. It was hypothesised that sketches would also be improved. Two experiments manipulating context were conducted, which found some conflicting results. In one experiment, the detailed context reinstatement impaired the composite quality while another experiment found a benefit for sketch composites not using any reference materials. These results indicate that sketch composites can be improved by providing witnesses with visual cues during construction and using memory enhancement techniques.