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Applied Ergonomics 44 (2013) 703e709

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Applied Ergonomics

journal homepage: www.elsevier .com/locate/apergo

Hostile intent in public crowded spaces: A field study

Peter Eachus a,*, Alex Stedmon b, Les Baillie c

a School of Social Work, Psychology and Public Health, Allerton Building, Frederick Road Campus, University of Salford, Salford,Greater Manchester M6 6PU, UKbHuman Factors Research Group, University of Nottingham, UKcWelsh School of Pharmacy, University of Cardiff, UK

a r t i c l e i n f o

Article history:Received 9 March 2011Accepted 18 May 2012

Keywords:Hostile reconnaissanceTerrorismDetectionDeceptionPheromones

* Corresponding author. Tel.: þ44 1612952428.E-mail address: p.eachus@salford.ac.uk (P. Eachus)

0003-6870/$ e see front matter � 2012 Elsevier Ltdhttp://dx.doi.org/10.1016/j.apergo.2012.05.009

a b s t r a c t

Hostile reconnaissance is vital to successful terrorist activity. Individuals carrying out this activity arelikely to experience raised levels of stress and this will manifest itself at biological, physiological,psychological and behavioural levels, providing an opportunity for detection. A field trial was undertakenin an ecologically valid environment measuring variables considered likely to be salient during hostileintent. The parameters examined in the field trial varied in a predictable manner and suggest thatstressed individuals secrete a volatile steroid based marker that could form the basis for remotedetection. Thus, overall the findings of this research provide a validated model of hostile intent that canbe used by other researchers to test interventions aimed at detecting or deterring hostile intent.

� 2012 Elsevier Ltd and The Ergonomics Society. All rights reserved.

1. Introduction

1.1. Terrorism and hostile reconnaissance

Modern terrorist operations are sophisticated, and to besuccessful they must be based upon sound intelligence. Thisintelligence can take many forms and may be obtained usinga variety of techniques and technologies (Linett, 2005). Open-source intelligence is readily available via the Internet and withthe advent of web-based interactive maps and web-sharing media(e.g., photos of public crowded spaces) terrorists can actually viewtargets at street level. While this level of intelligence may be usefulin the initial planning stages, for a successful campaign moredetailed intelligence will be required and this can only be obtainedby physical reconnaissance of an intended target (Cannon, 2004).

Most, if not all, successful terrorist operations have involvedactive hostile reconnaissance before the attack was launched.Subsequent investigations revealed that both the attack on theWorld TradeCentre in 1993 and the bombingsof theUS embassies inKenya and Tanzania a few years later, which resulted in mass casu-alties, were preceded by years of information gathering and covertsurveillance (Cain, 2009). Pre-operational reconnaissance alsoseems to have been a feature of the bombings in London on July 7th2005 and the ricin attack on the Tokyo subway ten years earlier.

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and The Ergonomics Society. All ri

A number of research programmes have been designed toinvestigate the possibility of detecting hostile intent including thatsponsored by the Department of Homeland Security ‘Hostile IntentDetection: Automated Prototype Project’. This project aims todemonstrate real-time, non-invasive, and culturally independent,video extraction algorithms to identify unknown or potential secu-rity threats. Commercial examples include ‘Cogito’, an expert systemaimed at detecting individuals who may have terrorist intentions.The system is a sophisticated lie detection system, and while thedeveloper, Suspect Detection Systems claims an 85% detection rate,there is very little published validation data that would substantiatethis. A further problemwith this system is that it requires the peoplebeing investigated to sit in a dedicated booth for the collection ofdata. While this might be acceptable at airports or border controlpoints it would have little value in crowded, free-flowing environ-ments such as shoppingmalls andmass transit hubs. Consequently, ifsuch a system could deliver a high detection rate it still leavesa substantial gap in the detection of hostile intent in public spaces. IntheUSAtheDepartmentofHomelandSecurityhasadopteda systemsapproach, which aims to integrate human factors and behaviouralscience research into thedevelopmentof human systems integrationstandard. Although initially being used in the development ofambulances it will also have utility in the design of security systemsfor transportation hubs such as airports and railway stations.

1.2. Hostile reconnaissance and stress

One of the basic assumptions of this current study is that due tothe risk of being intercepted in some way, individuals who are

ghts reserved.

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undertaking hostile reconnaissance activities will find the experi-ence stressful to some degree. This stress will manifest itselfbehaviourally, psychologically, and physiologically (Selye, 1976). Itmay also present biological indicators, via stress pheromones andin order to address these factors, this current research took anintegrated approach to understanding and modelling hostile intent(Fig. 1).

The underlying premise is that an individual involved ina criminal or terrorist act (such as hostile reconnaissance) mayprovide data across any or all four factors. The psychology andphysiology of stress is well understood (Gray, 1988) and instru-ments for the measurement of these parameters are readily avail-able; for example the State Trait Anxiety Inventory (Marteau andBekker, 1992) and the ‘BioHarness’ (Biopac Systems, Zephyr Tech-nology Ltd). However, the biology of stress in terms of theproduction of stress pheromones is rather less well developedalthough several studies claim to have identified the presence ofpheromones in participants who have been subjected to stressfulexperiences (Chen et al., 2006; Mujica-Parodi et al., 2008).

1.3. Pheromones and alarm signals in body odour

The role of pheromones in communication across the animalkingdom is well documented. For example Regnier and Law (1968)reviewed the evidence for chemical communication by insects andconcluded that there are a variety of pheromones that are used indifferent contexts (e.g., attracting/detecting mates and alarm sig-nalling).When placed under stressful conditions, insects are knownto release alarm pheromones that warn other colony members ofan impending threat (e.g., as happens with bees and ants). Therelease and detection of pheromones is by no means limited toinsects, and has been demonstrated in a number of animals (Wyatt,2003). However, whilst olfactory communicationmay be importantin other species, its value in human communication is as yetunproven.

One of the difficulties associated with the characterisation ofhuman fear pheromones, is their low concentrations in secretedmedia (Butenandt et al., 1961; Boeckh et al., 1965; Grosser et al.,2000; Millar, 2002). It is also assumed that alarm pheromones inhumans must be volatile to ensure greater penetration of theolfactory membrane (Millar, 2002) and this may lead to practicaldifficulties in the capture, storage and analysis of samples. Never-theless there has been some speculation in the literature that

Fig. 1. The integrated factors of hostile intent.

people may secrete a stress pheromone in their body odour (sweat)under stressful conditions (Chen et al., 2006).

Mujica-Parodi et al. (2008) examined differences in brainactivity in the amygdala, a structure activated in humans byemotional arousal and in animals by alarm pheromones, and foundthat exposure to ‘stress sweat’ (collected from first-time tandemskydivers) caused significantly greater stimulation than exposureto ‘exercise sweat’ (collected from people using a treadmill). Theyalso found that that exposure to stress sweat had a behaviouraleffect, with participants showing a significant increase in accuracyof detection for ambivalent threat. Based on these results theyconcluded that sweat collected during acute emotional stress, andsubsequently presented to an unrelated group of individuals,produced significant brain activation in regions responsible foremotional processing without conscious perception of distinctodour (Mujica-Parodi et al., 2008).

One explanation for reactions to stress sweat is an increase inthe level of cortisol, a hormone that correlates with stress in sali-vary samples (Haussmann et al., 2007). However, investigations ofolfactory responses to, and the chemical profiles of, sweat samplesproduced under stressful situations have not yet validated ifcortisol present in sweat is responsible for a ‘smell of fear’ (Ackerlet al., 2002) and the fundamental question of whether humansare capable of secreting a fear ‘marker’ still remains. The level ofcortisol in the body is sensitive to many factors aside from stress,including time of day, weight, state of health and age. Therefore, itis not possible to determine whether an individual is stressed bya single analysis and the degree of stress that an individual is underis ascertained by comparing cortisol levels from two or more testsand reference to personal baselines. Also, whilst cortisol is presentin both saliva and sweat, saliva is the preferred medium of analysis(Prunty et al., 2004) and there is currently no published evidence toshow the diagnostic value of cortisol levels in sweat.

Some studies have employed Gas ChromatographyeMassSpectrometry (GCeMS) to elucidate the chemical components ofsweat samples (Curran et al., 2005; Penn et al., 2007). The ability ofthis technique to isolate complex combinations of chemicals,coupled with its high sensitivity provides an ideal tool for investi-gating stress components in sweat samples.

1.4. The potential for human stress components

Should a volatile alarm pheromone be discovered and charac-terised from human sweat it would pave the way for the devel-opment of detection devices to determine the presence andconcentration of such a compound in an individual’s odour. Thistechnology would be valuable in many areas including counter-terrorism and behavioural science as well as having a muchbroader appeal, as it would enable people to gauge the stress levelsof an individual at a given time.

Portable detection devices for volatile chemical compounds arealready employed by forensic scientists and most are based aroundGCeMS techniques. Other approaches to ‘field’ collection of volatilematerials include Solid PhaseMicro-Extraction (SPME), which trapsvolatile analytes in micro-fibres for later analysis.

Several approaches to threat detection are available or underdevelopment including explosives detection by insects (Rains et al.,2008) detection of volatile chemicals emitted by explosives andnarcotics using static and portable devices (Smiths Detection,http://www.smithsdetection.com) and more familiar devices suchas the alcohol breathalyser which rely on a detectable reaction tocompounds in human breath. Regardless of the policies, proce-dures, or technologies that are developed to combat hostile intent,a methodology for testing the validity and reliability of differentapplications is required. The purpose of the research described here

P. Eachus et al. / Applied Ergonomics 44 (2013) 703e709 705

was to inform the development of such a methodology for fieldresearch whilst also exploring the potential for human stresscompounds.

1.5. A user-centred integrated approach

An integrated and user-centred approach was adopted for thefield study in order to understand and model hostile intent acrossthe four key factors:

� Biological characteristics (cortisol data and stress pheromones)e in this study cortisol and sweat pad data were collected as aninnovative means of investigating biological traits of peopleconcealing their intent. Cortisol is a validated measure ofstress/arousal and this was collected to support the biologicalvalidity of the study as well as provide support for the moreinnovative stress pheromone data.

� Physiological characteristics (heart-rate, respiration and bodytemperature) e various data were collected in order to inves-tigation the physiological profiles of participants who wereconcealing their intent. This approach was also used to helpvalidate the design of increasing arousal levels through thefield study.

� Psychological responses (subjective measures of stress) e thisapproach and the measures used, was designed to assess thepsychological state of participants across the different condi-tions of the field study.

� Behavioural factors (CCTV recording data) e video recordingsof participants were used to investigate if behaviours associ-ated with hostile intent could be detected by others.

By taking an integrated approach it was possible to investigateaspects of concealed intent from a user-centred perspective byincorporating data focused on user responses to the tasks and theiroperational environment.

2. Field study Rationale

The design of this study was based on the assumption thatsomeone engaged in hostile reconnaissance runs the risk of beingdetected, questioned or arrested. This knowledge will have conse-quences in terms of the individual’s behaviour, psychological stateand physiological and biological responses. The purpose of thisstudy was to determine how these stress responses might manifestthemselves and what influences they might have on the behaviourof the individual concerned.

In this field study, hostile reconnaissance was simulated ina public crowded space (i.e., a large shopping mall). Baseline datawere collected before each participant was placed in variousstressful situations (i.e., Low Intent versus High Intent) and theirbiological, physiological, psychological responses and status weremonitored. The behaviour of the participants in the Low Intent andHigh Intent conditions was also recorded on CCTV (via securitycameras in the shopping mall) where a second group of partici-pants were recruited to explore behavioural attributes associatedwith stress.

3. Method

3.1. Participants

Asmales tend to be better secretors of any pheromones (Mujica-Parodi and Strey, 2006) 20 male participants were recruited fromundergraduate or postgraduate students at the University of Sal-ford. Although not specifically analysed in this study, age data

ranged between 18 years and 25 years. For the second part of thestudy 15 male and female students viewed CCTV recordings ofparticipants from the first part of the study. All participantsconfirmed that theywere not taking anymedicines or receiving anymedical treatment and that they felt fit and well.

3.2. Materials and apparatus

Participants selected for the first phase were provided with anodourless soap to wash with prior to the investigation. Due to thedetailed nature of this study the specific measures are detailedbelow:

� Biological characteristics e levels of salivary cortisol were ob-tained using Sarstedt ‘Salivette’ testing kits, stored at �20 �Cprior to analysis. In order to collect pheromone data, sweatsamples were obtained from cotton pads secured in thearmpits of participants with microporous tape. Followingcollection of the sweat samples, the pads from the participantsdominant side were placed in 50 ml sample tubes containingHPLC grade acetone (10 ml) and stored at �20 �C for lateranalysis using Gas ChromatographyeMass Spectrometry(GCeMS).

� Physiological characteristics e physiological data were ob-tained using a wireless ‘BioHarness’ (Biopac Systems, ZephyrTechnology Ltd) uploaded to a computer for analysis usingAcqKnowledge software. Recordings were carried out ina constant temperature (20�c) environment.

� Psychological factors e self-reported levels of stress were ob-tained using the short form of the State Trait Anxiety Inventory(STAI) questionnaire (Marteau and Bekker, 1992). This is a six-item scale was derived from the original extended scaledeveloped by Spielberger (1983). It required participants torecord how they were feeling at that moment using a fourpoint Likert scale.

� Behavioural factors e CCTV recordings were collected ofparticipants conducting the experiment. These were thenshown to the second group of participants in the second part ofthe study to investigate any detectable behaviours associatedwith hostile intent.

3.3. Design and procedure

The hostile intent study progressed through three stagesincluding: pre-trial preparation, baseline data collection, and themain study that contained two traverses of the shopping mall.Participants were informed that the focus of the investigation wasthe relationship between stress and shopping and that the studywould take approximately 2 h to complete. The CCTV behaviourstudy was then conducted with a second group of participants.Both studies were run as separate ‘within-subjects’ designs.

In the pre-trial preparation, participants were supplied witha bottle of scent-free shower gel that they were required to use onthe morning of the experiment, instructed to avoid using perfumes,body sprays and deodorants, and to refrain from alcohol, odorousfood (such as curry), cabbage, and asparagus in the 24 h prior totaking part in the study.

Baseline data collection took place in the psychoephysiologicallaboratory at the University of Salford. Participants were seated andput on the Bioharness and cotton wool pads were attached undertheir armpits using micro-porous tape. Participants completed theSTAI questionnaire and provided a salivary cortisol sample. Partic-ipants then sat quietly for 15 min during which time baseline datawere recorded for heart rate, respiration and body temperature.

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Afterwards, another salivary cortisol sample was collected andanother STAI questionnaire completed. Following this, the underarm pads were removed. The pad from the dominant armpit wasplaced in a container of 10ml of acetone, and the secondwas placedin a ziplock bag. Dominant arm pads were collected to control forany under arm dominance effects. All samples were placed ina freezer as soon as possible after collection. Participants had beenpreviously informed that for completion of this part of the exper-iment they would be paid £10.

In the main trial, participants were transported to a nearbyshopping mall. The purpose of this phase of the study was to obtainmeasures of arousal while traversing a crowded public place. It waspredicted that there would be a significant increase in thesemeasures compared with the baseline measures obtained in thelaboratory. All data were collected between 10:00am and middaywhentheshoppingcentrewas reasonablybusybutnotovercrowded.

Participants were instructed to make traverses of the shoppingmall. They were shown a map of the mall and given instructions ofthe route they were to take. They were told that in order for theresearchers to be able to confirm that the correct route had beenmade, they were to take photographs at six specific locations. Thefirst traverse was designated as a ‘Low Intent’ condition andparticipants were informed that if they completed the tasksuccessfully they were to be paid £20.

The Bioharness and pheromone pads were re-attached, a sali-vary cortisol sample obtained, and the STAI questionnairecompleted. The Bioharness was activated when the participantbegan their traverse through the shopping centre. Although theparticipant had been told that the traverse was untimed, theresearcher used a stopwatch to record the time taken. The traversewas a circular route and on their return the Bioharness data wasdownloaded and the sweat samples collected. A further salivarycortisol sample was also obtained and an STAI questionnaire wascompleted.

The final part of the main study was designed as the ‘HighIntent’ condition to increase stress levels in an attempt to mimica hostile reconnaissance activity. Participants were informed thatfor this part of the study, their traverse would be timed and thatthey had to complete it 10% faster than their previous traverse time.Participants were also informed that CCTV and plain-clothessecurity staff would be looking for any unusual or suspiciousbehaviour. Although the security guards would not know thespecific identity of the participants, each participant was told thattwo previous participants had been detected (this was not actuallythe case). Participants were also informed that if they agreed to takepart in the final activity of the experiment, and were successful,they would be paid a further £70. However, if they were observed,or did not beat the timed deadline then they would not only losethe £70, but theywould also lose the £20 they had been paid for thefirst traverse. To be sure they understood these instructions theywere given a written version that required their informed consentbefore continuing.

The second traverse was essentially the same route as the firstwith the same data collected. At the end of the second traverse, allparticipants were informed that they had been successful andwould receive the full payment of £100 (£10 baseline payment, £20first traverse payment and £70 second traverse payment). Theywere also informed that following completion of the study theywould receive a debriefing letter with summary findings.

Participants who had traversed the shopping mall in the LowIntent and High Intent conditions had been recorded on CCTVinstalled in the shopping mall. In the second part of the study(behavioural analysis) a second group of participant were pre-sented with recordings of the two participants who had the lowestand highest STAI questionnaire scores for the High Intent condition

(i.e., the person who responded the least and the person whoresponded the most to the stress induction). The CCTV recordingswere presented in pairs (e.g., Low Intent followed by High Intent)but these were randomised. For each of the four CCTV clips,participants rated the perceived stress levels of the shopping mallparticipants using a 10-point Likert scale (varying from 1 ¼ LowStress to 10 ¼ High Stress).

3.4. Ethics

Before any data were collected the research proposal wasconsidered by the University of Salford Ethics Committee. Theywere satisfied that the proposed research met the ethical standardsrequired. Agreement with the management of the shopping mallwas obtained and they were also informed when the specificresearch was taking place.

4. Results

This field trial produced data across all four factors (e.g., bio-logical, physiological, psychological and behavioural). In order todemonstrate the validity of this model of hostile intent it wasimportant to illustrate that it is possible to induce levels of stressduring the High Intent condition of the study that were signifi-cantly higher than either the Baseline and/or Low Intent conditions.

In the results presented below, the Baseline measures werethose obtained under laboratory conditions with participants ina relaxed state with minimal stress. The Low Intent condition refersto the first traverse of the shopping centrewith no attemptmade toinduce stress. In the High Intent condition, participants werecompleting the traverse under the condition that simulated hostileintent with high levels of induced stress. Nineteen of the twentymale participants completed all three parts of the experiment.

4.1. Biological characteristics

4.1.1. Cortisol AnalysisSalivary cortisol samples were stored at�20 �C prior to analysis.

The frozen salivettes were thoroughly thawed and centrifuged at1000 � G for 2 min using an ELISA competitive kit (Salimetrics Ltd)with no modifications to the manufacturers guidelines.

Measures of salivary cortisol were obtained at the start and endof each of the three conditions, as described in the procedure. Theinterval of time between obtaining the first and second samples ofcortisol varied slightly within individual participants but wasapproximately 15 min and it was hypothesised that changes incortisol levels during this period would be an indication of changesin arousal levels. Therefore the analysis conducted looked forsignificant changes in levels of cortisol across the three conditions(Table 1).

The mean levels of cortisol were compared using a 1�3 within-subjects ANOVA. Data sphericity could not be assumed (p < 0.05)and so a GreenhouseeGeisser correction was taken for the signif-icant difference that was observed [F(1.46, 26.22) ¼ 11.949,p < 0.001]. Post-hoc comparisons between the different conditionsrevealed that there was no significant change between the Baselineand Low Intent condition (p> 0.05) however, an increase in cortisollevels during the High Intent conditionwas found to be statisticallysignificant to the other conditions (p< 0.05). This finding illustratesthat changes in stress occurred during the High Intent conditionthus giving support to the model of hostile intent.

4.1.2. Stress pheromonesTo obtain GCeMS profiles of the sweat samples, a Waters GCT

Premier HP6890N GC machine was used. The analytes were

Table 1Changes in levels of cortisol.

Condition N Mean (SD)

Baseline 19 0.02 (0.60)Low Intent 19 �0.08 (0.26)High Intent 19 0.31 (0.41)

P. Eachus et al. / Applied Ergonomics 44 (2013) 703e709 707

desorbed in the injector port at a temperature of 200 �C. The massspectrometer used was a Waters ESI with the detector in full scanmode (50e800 Da), relative to the lock mass (mass spectrometrygrade heptacosa). The Mass spectrometer was equipped with a NistMS Search 2.0 library searching facility.

Sweat samples collected in pads from the axilla of the dominantarmpit of participants during the Baseline, Low Intent and HighIntent conditions were analysed using GCeMS. There was nooverall change in the peaks from the baseline to the more stressedsamples, apart from the peak at approximately 35.5 min (peak A inFig. 2 below). Mass spectrum analysis of this peak identified thecompound as Sitosterol. However the presence of several frag-ments of higher mass in the spectrum suggest that Sitosterol islikely to be a breakdown product of a larger sterol which is frag-mented, post collection by the analysis process.

The relative increase in sterol concentration above baseline foreach individual compared to their baseline level is shown in Fig. 3.With the exception of participant 1, the concentration of theunidentified sterol is dramatically increased in response to the testconditions.

Since no trend was observed in terms of an increase/decrease inthe concentration of the sterol following the first and secondtraverses these results suggest that the sterol is a marker for, ratherthan a gauge of, the level of stress. When the changes in sterollevels were compared with changes in cortisol levels it was foundthat the concentration of the sterol increased as a function of stressregardless of the cortisol levels in the saliva samples.Whilst cortisollevels may change differentially when certain individuals are pre-sented with stressful situations, they have no control over thesecretion of a stress pheromone in sweat. The sterol is releasedregardless of cortisol levels. Therefore, the determination ofwhether a person is stressed or not may be more reliable by ana-lysing their sweat rather than their saliva. This finding supports the

34 34.5 35 35.5 36 36.5 37 37.5-1

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1

2

3

4

5

6

7x 10

4

A

B

C D

Fig. 2. Peaks identified from GCeMS traces as varying between baseline and stressedsamples.

argument for a compound that is secreted during times of stress.Further work will be required to confirm that this compound isrelated to a stress pheromone.

4.2. Physiological characteristics

Heart rate: mean heart-rate data (beats/minute) werecompared using a 1 � 3 within-subjects ANOVA. A significant maineffect was observed [F(2,36) ¼ 71.526, p < 0.001]. Post-hoccomparisons between the three conditions indicated a significantdifference in heart rate between the Baseline and Low Intentconditions (p < 0.001) and the Low Intent and High Intent condi-tions (p < 0.001) as illustrated in Table 2.

It should be noted that the differences between the Baseline andLow Intent can be explained by the difference in activity (seated vswalking). However, in relation to the Low Intent and High Intentconditions, the task and movement involved were essentially thesame. Although the High Intent condition had a time factorattributed to it and a marginal amount of the heart rate differencescan attributed to increased energy expenditure, it is suggested thatthe major contributor to the difference observed was the level ofinduced stress afforded by the nature of the task.

Respiration: was measured in breaths/minute and would beexpected to increase in times of stress. Table 3 illustrates the meanlevels of respiration for participants across the three phases of thefield study.

The mean respiration data were compared using a 1 � 3 within-subjects ANOVA. Data sphericity could not be assumed (p < 0.05)and so a Greenhouse-Geisser correction was taken for the signifi-cant difference that was observed [F(1.46, 26.21) ¼ 73.037,p < 0.001]. Post-hoc comparisons between the Baseline and LowIntent conditions were statistically significant (p < 0.001). Likewisethe difference between Low Intent and High Intent conditions wasalso statistically significant (p < 0.01). The caveat applied to theheart rate data must also be applied when examining the respira-tion data. An increase in Low Intent over the Baseline conditionwould be expected, but the increase observed between the HighIntent and Low Intent conditions, suggested a response to addi-tional induced stress.

Body Temperature: skin temperature was measured using theinfrared sensor within the BioHarness. Mean and standard devia-tion data are presented in Table 4.

Although the data illustrated a trend in the predicted directionwith body temperature in the High Intent condition being slightlyelevated relative to the other two conditions, this difference failedto reach statistical significance (p > 0.05).

4.3. Psychological responses

The STAI questionnaire was completed by participants at thestart and end of each of the three conditions. Total scores rangedfrom 6 (minimum) to 24 (maximum). As can be seen in Table 5, self-reported levels of stress increased across the three conditions.

The mean STAI data were compared using a 1 � 3 within-subjects ANOVA. Data sphericity could not be assumed (p < 0.05)and so a Greenhouse-Geisser correction was taken for the signifi-cant difference that was observed [F(1.54, 27.73) ¼ 28.859,p < 0.001]. Post-hoc tests confirmed that the STAI scores obtainedin the High Intent condition were significantly higher than the LowIntent condition (p< 0.001) and that the scores obtained in the LowIntent condition were significantly higher than those obtained atBaseline (p < 0.01). This finding suggested that participants in theHigh Intent condition experienced greater levels of stress, lendingfurther support for the validity of the model of hostile intent.

Fig. 3. The relative concentration and increase of Sitosterol above baseline (peak A) between Low Intent (White) and High Intent (Black).

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4.4. Behaviour analysis

CCTV behaviour: the highest and lowest self-rated participantCCTV recordings from the shopping mall experiment were rated bythe second group of participants using a 10-point scale where1 ¼ low and 10 ¼ high. Comparisons within and between each pairof CCTV recordings, using related and independent t-tests respec-tively found no significant differences in the stress ratings(p> 0.05). Table 6 represents the results of the behavioural analysis.

Interestingly, the correlations between the pairs of CCTVrecordings also failed to reach significance (p > 0.05) suggestingthat stress did not have an immediately observable impact onbehaviour in this study.

Table 3Respiration (breathes/minute).

Condition N Mean (SD)

Baseline 19 16.24 (2.07)Low Intent 19 23.89 (3.50)High Intent 19 26.97 (5.08)

5. Discussion

The purpose of the field trial was to improve and test theecological validity of our Model of Hostile Intent. In order to do thisthe field trial had to establish that it was possible to simulate theconditions an individual engaged in hostile reconnaissance mightencounter. If successful this simulation would induce biological,physiological, psychological, behavioural concomitants of stressduring the High Intent phase of the experiment.

The task in the High Intent phase involved reconnaissance,concealment, and a degree of self-control, all of which contributedto the experience of stress. Therefore it constituted a very goodapproximation of hostile intent in a public crowded space (e.g.,moving around a public space, taking photos of specific attributesin the environment without being detected). Since the psycholog-ical, physiological and to some extent biological parameterschanged in the predicted manner of a person engaged in hostileintent, the simulation of hostile reconnaissance and a model ofhostile intent was, to a large extent, achieved.

Table 2Heart rate (beats/minute).

Condition N Mean (SD)

Baseline 19 79.34 (15.30)Low Intent 19 109.14 (21.18)High Intent 19 134.66 (26.18)

The behavioural analysis did not reveal the predicted outcome,in that it was not possible to identify specific stress behaviours thatmight indicate hostile intent. During periods of stress, when thefight/flight response is initiated, blood flow is redirected from theextremities to the body core in order to facilitate increases in heartrate and respiration associated with increased arousal (Selye, 1974).Long et al. (1990) illustrated that increases in body temperature(e.g., hyperthermia) could be induced in rats through psychologicalstress and in humans there is evidence that appears to showa relationship between body temperature and improved perfor-mance, alertness and visual attention (Wright et al., 2002).However, this aspect of the research was important in that it hasprovided researchers with a CCTV database of behaviours that havebeen produced during a simulation of hostile intent. This facilitycan therefore be used by others to test behavioural hypothesesassociated with hostile intent in the full knowledge that thebehaviours being observed are those of people experiencing thebiological, physiological and psychological changes that are likelyto be felt by those involved in hostile reconnaissance.

All the participants in the field trial were young white malesand, arguably, future terrorist activity will see representatives fromethnic/marginalised groups and more females involved. In thisstudy the secretion and detection of stress pheromones was animportant part of the investigation. Since males appear to be betteremitters of pheromones it seemed reasonable to use this approach

Table 4Body temperature (�C).

Condition N Mean (SD)

Baseline 19 32.90 (1.06)Low Intent 19 32.95 (1.08)High Intent 19 33.07 (1.14)

Table 5STAI.

Condition N Mean (SD)

Baseline 19 8.84 (2.42)Low Intent 19 10.78 (2.78)High Intent 19 13.07 (2.63)

Table 6CCTV stress ratings (1e10).

Pair CCTV sample N Mean (SD)

1 A 15 3.80 (1.74)1 B 15 3.73 (1.33)2 C 15 3.60 (1.80)2 D 15 4.06 (2.19)

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in the first instance, however, given that gender roles in terroristactivities are likely to become more fluid, these assumptions willneed to be examined by further research.

Amethodological limitationwith this researchwas the potentialconfounding of stress and increased exertion. The participants inthe High Intent conditions knew that they had to complete thesecond traverse more quickly than their first traverse (e.g., within10% of their original time) and therefore increased exertion couldhave elevated some of the measures taken (e.g., respiration andheart rate). However given that other measures of stress that wouldnot have been expected to change through exertion (e.g., STAI dataand cortisol) also showed increases, this lends support to ourconclusion that the High Intent participants were indeed experi-encing greater levels of stress.

A fundamental conceptual issue with this type of researchconcerns the ecological validity of the study (i.e., to what extentdoes the proposed model mimic the reality that an individualexperiences during hostile reconnaissance). Is it possible thatterrorists, with sufficient training, might be able to suppress somefeelings of stress and thus appear calm during hostile reconnais-sance? This would seem highly unlikely given that even highlytrained combat troops still experience feelings of stress prior toactive engagement (Shepherd, 2003). It would therefore seemreasonable to conclude that individuals undertaking hostilereconnaissance would respond at biological, physiological andpsychological levels in the way that our model proposes. Behav-iourally, individuals may well be able to exert far more control andtherefore outwardly appear calm. This would concur with theresults of the CCTV observations that failed to find any significantdifferences between the Low and High Intent conditions.

6. Conclusion

The research presented here has demonstrated that it is possibleto simulate behaviour during hostile reconnaissance. Furthermorewehave demonstrated a biological response to stress and concealedintent through pheromone production, to distinguish betweenthose engaged in hostile intent compared to those who are not.Indeed these results suggest that individuals placed under stresssecrete a volatile steroid basedmarker, which has the potential to beexploited as the basis of a remote detector. In thisfield trial of hostileintent the predicted changes across psychological, physiological andbiological parameters have all been confirmed. It is suggested thatthis validation of the model will prove fruitful in further researchthat seeks to explore hostile intent.

Acknowledgement

This research was funded by Home Office contract: CDE12123.

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