Adopting a multidisciplinary approach to maximising performance during military visual search tasks.

During the conflicts in Afghanistan and Iraq, many UK military personnel were killed or injured by improvised explosive devices (IEDs). Insurgents sought to develop new ways of concealing and detonating IEDs, and UK forces invested significantly in finding increasingly effective methods of detecting and avoiding them. Between 2010 and 2014 the UK's Defence Science and Technology Laboratory's Human and Social Sciences Group (HSSG) was asked to investigate the factors that might affect the performance of specialist search teams in the identification of IEDs. They sought to ascertain ways to improve effectiveness and maximise safety through training, human factors advice on equipment design, and recommendations on changes to tactics techniques and procedures. This paper provides a short summary of some of the research conducted that underpinned the advice and recommendations that were provided. The research conducted by HSSG, in collaboration with industry and academia, helped ensure that search teams had the best possible training, advice and equipment.

The importance of search strategy for finding targets in open terrain.

A number of real-world search tasks (i.e. police search, detection of improvised explosive devices (IEDs)) require searchers to search exhaustively across open ground. In the present study, we simulated this problem by asking individuals (Experiments 1a and 1b) and dyads (Experiment 2) to search for coin targets pseudo-randomly located in a bounded area of open grassland terrain. In Experiment 1a, accuracy, search time, and the route used to search an area were measured. Participants tended to use an 'S'-shaped pattern with a common width of search lane. Increased accuracy was associated with slower, but also variable, search speed, though only when participants moved along the length (as opposed to across the width) of the search area. Experiment 1b varied the number of targets available within the bounded search area and in doing so varied target prevalence and density. The results confirmed that the route taken in Experiment 1a generalizes across variations in target prevalence/density. In Experiment 2, accuracy, search time, and the search strategy used by dyads was measured. While dyads were more accurate than individuals, dyads that opted to conduct two independent searches were more accurate than those who opted to split the search space. The implications of these results for individuals and dyads when searching for targets in open space are discussed.

An examination of the processing capacity of features in the Thatcher illusion.

Detection of the Thatcher illusion (Thompson, Perception, 9:483-484, 1980) is widely upheld as being dependent on configural processing (e.g., Bartlett & Searcy, Cognitive Psychology, 25:281-316, 1993; Boutsen, Humphreys, Praamstra, & Warbrick, NeuroImage, 32:352-367, 2006; Donnelly & Hadwin, Visual Cognition, 10:1001-1017, 2003; Leder & Bruce, Quarterly Journal of Experimental Psychology, 53A:513-536, 2000; Lewis, Perception, 30:769-774, 2001; Maurer, Grand, & Mondloch, Trends in Cognitive Sciences, 6:255-260, 2002; Stürzel & Spillmann, Perception, 29:937-942, 2000). Given that supercapacity processing accompanies configural processing (see Wenger & Townsend, 2001), supercapacity processing should occur in the processing of Thatcherised upright faces. The purpose of this study was to test for evidence that the grotesqueness of upright Thatcherised faces results from supercapacity processing. Two tasks were employed: categorisation of a single face as odd or normal, and a same/different task for sequentially presented faces. The stimuli were typical faces, partially Thatcherised faces (either eyes or mouth inverted) and fully Thatcherised faces. All of the faces were presented upright. The data from both experiments were analysed using mean response times and a number of capacity measures (capacity coefficient, the Miller and Grice inequalities, and the proportional-hazards ratio). The results of both experiments demonstrated some evidence of a redundancy gain for the redundant-target condition over the single-target condition, especially in the response times in Experiment 1. However, there was very limited evidence, in either experiment, that the redundancy gains resulted from supercapacity processing. We concluded that the oddity signalled by inversion of eyes and mouths does not arise from positive interdependencies between these features.

Discriminating grotesque from typical faces: evidence from the Thatcher illusion.

The discrimination of thatcherized faces from typical faces was explored in two simultaneous alternative forced choice tasks. Reaction times (RTs) and errors were measured in a behavioural task. Brain activation was measured in an equivalent fMRI task. In both tasks, participants were tested with upright and inverted faces. Participants were also tested on churches in the behavioural task. The behavioural task confirmed the face specificity of the illusion (by comparing inversion effects for faces against churches) but also demonstrated that the discrimination was primarily, although not exclusively, driven by attending to eyes. The fMRI task showed that, relative to inverted faces, upright grotesque faces are discriminated via activation of a network of emotion/social evaluation processing areas. On the other hand, discrimination of inverted thatcherized faces was associated with increased activation of brain areas that are typically involved in perceptual processing of faces.

Perceptual and decisional factors influencing the discrimination of inversion in the Thatcher illusion.

The Thatcher illusion (Thompson, 1980) is considered to be a prototypical illustration of the notion that face perception is dependent on configural processes and representations. We explored this idea by examining the relative contributions of perceptual and decisional processes to the ability of observers to identify the orientation of two classes of forms-faces and churches-and a set of their component features. Observers were presented with upright and inverted images of faces and churches in which the components (eyes, mouth, windows, doors) were presented either upright or inverted. Observers first rated the subjective grotesqueness of all of the images and then performed a complete identification task in which they had to identify the orientation of the overall form and the orientation of each of the interior features. Grotesqueness ratings for both classes of image showed the standard modulation of rated grotesqueness as a function of orientation. The complete identification results revealed violations of both perceptual and decisional separability but failed to reveal any violations of within-stimulus (perceptual) independence. In addition, exploration of a simple bivariate Gaussian signal detection model of the relationship between identification performance and judged grotesqueness suggests that within-stimulus violations of perceptual independence on their own are insufficient for producing the illusion. This lack of evidence for within-stimulus configurality suggests the need for a critical reevaluation of the role of configural processing in the Thatcher illusion. (PsycINFO Database Record (c) 2011 APA, all rights reserved).