DOI:10.1068/p3402 What happens next? The predictability of natural behaviour viewed through CCTV cameras À

Can potentially antisocial or criminal behaviour be predicted? Our study aimed to ascertain (a) whether observers can successfully predict the onset of such behaviour when viewing real recordings from CCTV; (b) where, in the sequence of events, it is possible to make this prediction; and (c) whether there may be a difference between na|« ve and professional observers. We used 100 sample scenes from UK urban locations. Of these, 18 led to criminal behaviour (fights or vandalism). A further 18 scenes were matched as closely as possible to the crime examples, but did not lead to any crime, and 64 were neutral scenes chosen from a wide variety of noncriminal situations. A signal-detection paradigm was used in conjunction with a 6-point rating scale. Data from fifty na|« ve and fifty professional observers suggest that (a) observers can distinguish crime sequences from neutral sequences and from matches; (b) there are key types of behaviour (particularly gestures and body position) that allow predictions to be made; (c) the performance of na|« ve observers is comparable to that of experts. However, because the experts were predominantly male, the absence of an effect of experience may have been due to gender differences, which were investigated in a subsidiary experiment. The results of experiment 2 leave open the possibility that females perform better than males at such tasks. DOI:10.1068/p3402 À Parts of this research were previously presented in a paper given at the 24th European Conference on Visual Perception, Kus° adasi, Turkey. and Johnston (2001) found that head motion, as opposed to motion of facial features, provided useful information for recognising faces, and established that facial movements were beneficial in identifying gender. This motion effect has also been obtained with video images of famous faces degraded by blurring and pixelation (Lander et al 2001). However, to-date, although a large number of motion-based psychophysical studies have been conducted, we are not aware of any other ecologically valid psychophysical study (real people and real scenarios) carried out to investigate human observers' ability to predict criminal acts on the basis of the behaviours of human figures prior to those acts. This topic has an interesting application, because there is increasing use of CCTV systems in urban areas throughout the world. One question that may be raised about their use is whether a CCTV operator is capable of knowing whether something `bad' will happen soon in a given location, so as to be able to alert the security services to a possible risk. In CCTV control rooms, the outputs from the surveillance cameras are typically observed by control-room staff who then alert the security services if they detect a crime or antisocial act being committed; they also monitor situations they believe will result in such acts. These judgments of intentionality are based on visual information only. Mostly, the cues lie in the sequence of actions that are visible, although there may be occasions when an individual or individuals are suspected of unlawful behaviour because they are known offenders. From our observations of several control rooms in the UK, it became apparent that an operator often monitors a large number of (up to 50) TV screens simultaneously. This perceptual load is higher than an individual can cope with (Tickner and Poulton 1973), and therefore there is considerable interest in exploring the feasibility of an automated alerting system for possible violent/antisocial acts. Tickner and Poulton also suggested that females may perform better than males in identifying incidents. This is a topic we address in experiment 2. We carried out psychophysical experiments on human observers to ascertain whether they were able to make accurate judgments about what would happen later in scenes recorded by urban CCTV cameras. If the evidence suggests that prediction is possible, then the feasibility of producing a computational detector of the relevant behaviour is increased. The aims of this feasibility study were threefold. First, we wanted to investigate whether observers could predict criminal or antisocial behaviour from CCTV surveillance footage, and, second, whether na|« ve and experienced observers would differ in their judgments. Finally, and most importantly, we wished to examine whether there were identifiable behaviour patterns that might be predictive of unlawful acts. 2 Experiment 1 2.1 Method 2.1. 1 Participants. Fifty professional CCTV control-room operators, currently employed in monitoring urban CCTV surveillance cameras, and unfamiliar with the locations depicted in the video clips, were recruited as our èxpert' group. This group comprised operators aged between 20 and 62 years (mean  38:7 years), with surveillance experience ranging between 0.25 and 17 years (mean  5:7 years). There were forty-one males and nine females. The mean age of the males was 39.32 years (SD  11:68 years). The mean age of the females was 36.11 years (SD  7:36 years). First-year and second-year psychology undergraduates at the University of Bristol made up the `novice' group. They were aged between 18 and 21 years (mean  19:1 years) with forty-two females and eight males. The mean age of the females was 19.63 years (SD  0:83 years). The mean age of the males was 19.63 years (SD  0:74 years). Participants were tested individually in sessions lasting approximately 1 h 45 min. Experts were paid »7.50; novices earned a course credit. 88 T Troscianko, A Holmes, J Stillman, and coauthors