Conceptual and Perceptual Priming and Dissociation in ChronicPosttraumatic Stress Disorder

Nigel LyttleThe Belfast Health and Social Care Trust,

Belfast, Northern Ireland

Martin J. DorahyUniversity of Canterbury, Christchurch, New Zealand, and TheCannan Institute, Belmont Private Hospital, Brisbane, Australia

Donncha HannaThe Queen’s University of Belfast

Rafaele J. C. HuntjensUniversity of Groningen

Cognitive models of posttraumatic stress disorder (PTSD) assert that memory processes play a significantrole in PTSD (see e.g., Ehlers & Clark, 2000). Intrusive reexperiencing in PTSD has been linked toperceptual processing of trauma-related material with a corresponding hypothesized lack of conceptualprocessing. In an experimental study that included clinical participants with and without PTSD (N � 50),perceptual priming and conceptual priming for trauma-related, general threat, and neutral words wereinvestigated in a population with chronic trauma-induced complaints as a result of the Troubles inNorthern Ireland. The study used a new version of the word-stem completion task (Michael, Ehlers, &Halligan, 2005) and a word-cue association task. It also assessed the role of dissociation in threatprocessing. Further evidence of enhanced perceptual priming in PTSD for trauma stimuli was found,along with evidence of lack of conceptual priming for such stimuli. Furthermore, this pattern of primingfor trauma-related words was associated with PTSD severity, and state dissociation and PTSD groupmade significant contributions to predicting perceptual priming for trauma words. The findings shed lighton the importance of state dissociation in trauma-related information processing and posttraumaticsymptoms.

Keywords: posttraumatic stress disorder, perceptual priming, conceptual priming, dissociation

Ehlers and Clark (2000) pointed out that intentional recall of atraumatic event in posttraumatic stress disorder (PTSD) is gener-ally disjointed, disorganized, and deficient in detail, often withdistorted temporal ordering (see Kleim, Wallott, & Ehlers, 2008).Furthermore, individuals with PTSD experience a high frequency

of involuntarily triggered intrusive memories of the trauma. Thecontent of these intrusions (mainly sensory impressions and emo-tions) tend to occur in an unusually vivid way (Ehlers & Steil,1995; van der Kolk & Fisler, 1995). Although these intrusions areoften experienced as “coming out of the blue,” clinical observa-tions suggest that in fact a surprisingly wide range of triggers mayevoke them (Ehlers & Clark, 2000; Ehlers, Hackmann, & Michael,2004). For example, a woman experienced vivid intrusive imagesrelated to witnessing her partner’s murder in a drive-by shootingwhen she saw a certain shade of blue (e.g., on an advertisingbillboard poster), the same color as the assailants’ car. A furtherstriking feature of reexperiencing symptoms is that they oftenpossess a here-and-now quality. Thus, the sensory impressions areexperienced as if they were happening presently rather than beingmemories from the past. They lack the awareness of rememberingthat usually characterizes autobiographical memories (Brewin,Dalgleish, & Joseph, 1996; Foa & Rothbaum, 1998; Tulving,2002).

Several cognitive models of PTSD (see e.g., Brewin et al., 1996;Ehlers & Clark, 2000) posit that the distinctive characteristics oftrauma memory are due to the way information is processed duringtraumatic events. Models of autobiographical memory have distin-guished between memory for conceptual information and memory forperceptual information (Brown & Kulik, 1977; Conway & Pleydell-Pearce, 2000). Information processed conceptually refers to organizedtop-down processing of the situation/stimulus and integrating it intothe context through elaboration and organization, with inclusion of

Nigel Lyttle, Department of Psychology, The Belfast Health and SocialCare Trust, Belfast, Northern Ireland; Martin J. Dorahy, Department ofPsychology, University of Canterbury, Christchurch, New Zealand, andThe Cannan Institute, Belmont Private Hospital, Brisbane, Queensland,Australia; Donncha Hanna, School of Psychology, The Queen’s Universityof Belfast, Belfast, Northern Ireland; Rafaele J. C. Huntjens, Department ofClinical and Developmental Psychology, University of Groningen, Gro-ningen, the Netherlands.

This research was supported by Innovative Research Incentive VeniGrant 451-05-018 from the Netherlands Organization for Scientific Re-search (NWO) awarded to Rafaele J. C. Huntjens. The authors would liketo thank Rhonda Elder, Maria Shannon, Geraldine Hamilton, Mary Corry,Anne MacSherry, Geordie McRobert, Helen Elder, and Jim Gray, whoreferred participants to the study, and Martin Sawey and Gary McKeownfor their methodological assistance.

Correspondence concerning this article should be addressed to either MartinJ. Dorahy, Department of Psychology, University of Canterbury, Private Bag4800, Christchurch, 8140, New Zealand, or Nigel Lyttle, Neuropsychology,Department of Clinical Psychology, 4th Floor Bostock House, The RoyalHospitals, Grosvenor Road, Belfast, United Kingdom. E-mail:martin.dorahy@canterbury.ac.nz or nigel.lyttle@belfasttrust.hscni.net

Journal of Abnormal Psychology © 2010 American Psychological Association2010, Vol. 119, No. 4, 777–790 0021-843X/10/$12.00 DOI: 10.1037/a0020894

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higher order factors, such as meaning. Data-driven, or perceptual,processing refers to bottom-up processing of sensory impressions andperceptual characteristics, such as stimuli form and structure. Ehlersand Clark (2000) proposed that for individuals with chronic PTSD,processing during the signal traumatic event is largely limited toperceptual information, resulting in memory traces with a strongperceptual quality (see also Brewin & Holmes, 2003; Foa, Steketee, &Rothbaum, 1989). As a result, Ehlers and Clark (2000) suggested thatstimuli with associations to those encountered during the trauma (e.g.,seeing a color similar to that of the assailants’ car) gain a processingadvantage and result in cue-driven, unintentional retrieval of relatedtrauma memories (which are highly perceptual by nature; Brewin etal., 1996; Ehlers & Clark, 2000). This is referred to as perceptualpriming and is an operationalization of perceptual processing. Ehlersand Clark (2000) also proposed that in chronic PTSD strong associa-tive links exist between the cued and original stimuli (S-S associa-tions; e.g., the blue billboard poster and blue car) and between thestimuli and strong affective responses (S-R associations; e.g., the blueposter and terror), which also facilitates cue-driven retrieval (see alsoFoa et al., 1989). Conversely, integration of memories into the auto-biographical knowledge base is thought to inhibit cue-driven activa-tion and assist intentional recall (Conway & Pleydell-Pearce, 2000).Indeed, Roediger (1990) suggested an inverse relationship betweenperceptual and conceptual processing. In short, as conceptual process-ing increases, perceptual processing decreases. Thus, automatic, cue-driven retrieval associated with greater perceptual processing will bedecreased with greater conceptual processing.

Experimental studies have examined perceptual priming inPTSD using different samples (e.g., war veterans, Holocaust sur-vivors) and tasks (e.g., perceptual word identification, word-stemcompletion, white noise; Amir, McNally, & Wiegartz, 1996;Golier, Yehuda, Lupien, & Harvey, 2003; McNally & Amir,1996). For example, Michael, Ehlers, and Halligan (2005) foundenhanced perceptual priming for assault-related words in recentlyassaulted (�3 months) individuals with PTSD compared withrecently assaulted individuals without PTSD. They used a revisedversion of the word-stem completion task to assess perceptualpriming. Participants read aloud assault-related words, generalthreat words, and neutral words, each with matched neutral wordsthat had the same word stem and frequency in the English lan-guage (e.g., for-ced and for-mal). The authors suggested that thiscompetition for target words when completing word stems madethe task more sensitive to detecting priming effects compared withthe standard word-stem completion task, because either target ormatched (nontarget) words could be retrieved (see e.g., Golier etal., 2003).

A number of analogue studies have been conducted with non-clinical populations. Such studies attempt to simulate a trauma byexposing participants to pseudotraumas such as highly aversivefilms or traumatic picture stories (see e.g., Arntz, de Groot, &Kindt, 2005). There is evidence that self-reported and indepen-dently rated measures of data-driven processing are positivelyassociated with levels of analogue PTSD symptoms in nonclinicalpopulations (Halligan, Clark, & Ehlers, 2002; Kindt, Van denHout, Arntz, & Drost, 2008). In addition, analogue studies havefound evidence of enhanced perceptual priming for neutral “warn-ing” stimuli presented immediately prior to a traumatic story(Ehlers, Michael, Chen, Payne, & Shan, 2006). Ehlers et al. (2006)also found evidence that enhanced perceptual priming predicted

subsequent intrusions, supporting the theory that perceptual prim-ing plays a role in reexperiencing. Michael and Ehlers (2007)found evidence of an association between perceptual priming andsubsequent intrusions and that elaboration (through writing aboutthe experience; conceptually driven processing) reduced percep-tual priming and subsequent reexperiencing symptoms.

One candidate factor that may impede conceptual memory pro-cessing and give rise to perceptual processing in PTSD is peritrau-matic dissociation. Peritraumatic dissociation typically refers todissociative experiences during the course of a traumatic event(see e.g., Marmar, Weiss, & Metzler, 1997) and includes feelingdetachment from one’s body, sense of self, or external world.Many studies suggest peritraumatic dissociation is an importantpredictor in the development of PTSD (see e.g., Shalev, Peri,Canetti, & Schreiber, 1996), and a recent meta-analysis foundperitraumatic dissociation to be the best predictor of later PTSD(Ozer, Best, Lipsey, & Weiss, 2003). Ehlers and Clark (2000)suggested that peritraumatic dissociation might explain the “frag-mentation” of traumatic memories evident upon retrieval, becauseof the resulting inability to adequately integrate and processtrauma memories during and after encoding (Brewin, 2003). Dis-sociation during a traumatic event is argued to decrease focalattention, thereby interfering with conceptual processing and pro-moting a perceptual processing style that is characteristic of PTSD(Brewin et al., 1996; Siegel, 1995). Furthermore, peritraumaticdissociation could lead to a lack of self-referential perspectivewhen encoding the trauma memory, preventing elaboration andinclusion of higher order factors, such as personal meaning (Ehlers& Clark, 2000).

In a series of experiments Holmes, Brewin, and Hennessy(2004) found that spontaneous increases in state dissociation whileviewing a traumatic film were associated with increased reportedintrusions. Replicating and extending previous work (Ehlers et al.,2006), Michael and Ehlers (2007) found evidence that participantswith high trait and state dissociation showed relatively strongerperceptual priming than did those with low dissociation.

The present study investigated whether perceptual (data-driven)processing was inversely related to the degree of conceptuallydriven processing in a sample of PTSD patients with terrorist-related traumas in the Northern Ireland “Troubles” context.1 Thestudy aimed to replicate and extend the results of Michael et al.(2005) using a sample that presents with chronic and complextrauma-induced difficulties (see e.g., Dorahy et al., 2009; Dyer et

1 Troubles is a colloquial term that refers to the reemergence of politicallymotivated civil disturbance and sectarian violence in Northern Ireland, whichoccurred with great intensity and ferocity from the late 1960s. Approximately3,658 deaths are linked directly to the Troubles from July 1969 until April2001 (McKittrick, Kelters, Feeney, & Thornton, 2001) in a region with amodest population of just over 1.68 million (Northern Ireland Statistics andResearch Agency, 2002). In addition to direct deaths, thousands have been leftbereaved and countless thousands injured. Since the mid-1990s there has beenprogress toward a lasting peace, assisted by cease-fires from the main para-military organizations. The North and West Belfast catchment area, fromwhich all participants were recruited, represents an area of perhaps no morethan 10 square miles, containing half the population of Belfast (Curran &Miller, 2001). One third of all Troubles-related deaths, injuries, and incidentsof terrorist violence in the whole of Northern Ireland occurred in this area(Smyth, Morrissey, & Hamilton, 2001).

778 LYTTLE, DORAHY, HANNA, AND HUNTJENS

al., 2009). The test of perceptual priming was the revised word-stem completion task (Michael et al., 2005). The conceptual prim-ing task used a test of word-cue association (see Vaidya et al.,1997, Experiment 3), which presents cue words as semantic re-trieval aids for previously encoded words. Levels of perceptual andconceptual priming were determined for Troubles-related, generalthreat, and neutral words. Troubles-related words were utilized assymbolic stimuli (see Michael et al., 2005) representative ofTroubles-related traumatic experiences. To our knowledge, nostudy has attempted to measure conceptual priming in a PTSDpatient sample. In addition, the study also aimed to assess exper-imentally the role of dissociation in threat-related perceptual prim-ing. Thus, the associations between priming, state dissociation,trait dissociation, and symptom severity were examined. Thosewith PTSD were hypothesized to show enhanced perceptual prim-ing and impaired conceptual priming for Troubles-related wordscompared with controls without PTSD. In addition, higher percep-tual priming and lower conceptual priming for Troubles-relatedwords were predicted to be associated with higher PTSD symptomseverity. High trait and state dissociation were predicted to beassociated with higher levels of perceptual priming and lowerlevels of conceptual priming.

Method

Participants

During routine clinical contact, seven clinicians provided aparticipant information sheet to clients on their case list who metselection criteria. This sheet gave a general outline of the nature ofthe study and indicated that the aim was to understand more abouthow people think about traumatic events compared with how theynormally think about other experiences. Clients gave their therapista written consent slip giving permission for the researcher tocontact them to discuss involvement. In total, 66 people wereinvited to take part in the study.

Seven of the 33 participants invited for the PTSD sampledeclined. Those who declined reported being currently too dis-tressed to participate or having previously taken part in researchthat upset them. One participant was excluded due to Englishliteracy problems.2 From the original comparison sample of 33,five participants subsequently declined after receiving more infor-mation regarding the study or due to feeling too depressed toparticipate, and three were excluded due to literacy problems.

In the original PTSD sample the Posttraumatic Stress DiagnosticScale (PDS) agreed with clinician diagnosis in 32 out of 33 cases,and in the comparison sample there was one case that met theclinical threshold for PTSD on the PDS but not on the cliniciandiagnosis (� � .94). Both these participants were excluded fromthe study, due to literacy problems, as discussed in the last para-graph, and were not included in the final experimental sampleof 50.

The PTSD sample comprised 25 individuals (17 male, 8 female)who had all experienced traumatic events relating to the Troubles.The majority (88%) reported multiple traumas. Participants wererecruited from a government-funded service in Belfast, NorthernIreland, that treats those exposed to Troubles-related trauma. Theyranged in age from 24 to 63 years (M � 43.96, SD � 10.78) andwere included if they were between 18 and 65, met diagnostic

criteria for PTSD, and were in treatment. Those with a learningdisability, significant traumatic brain injury, a diagnosed psychoticdisorder, current substance abuse, active suicide risk, or insuffi-cient knowledge of English or literacy problems were excluded.

The comparison sample comprised 25 (17 male, 8 female)participants recruited from Adult Mental Health Services in thesame catchment area and in the same manner as the PTSD sample.The majority of comparison participants (80%) reported directTroubles-related trauma and multiple traumas (72%). However,they did not meet the clinical threshold for PTSD on the basis ofeither treating clinician diagnosis or independently administeredPDS. The remaining exclusion criteria were the same as for thePTSD sample. Comparison participants’ ages ranged from 20 to 65years (M � 42.8, SD � 14.33).

Measures

As well as completing perceptual and conceptual encoding andretrieval tasks, participants completed the PDS, the DissociativeExperiences Scale, the Brief Symptoms Inventory, the Clinician-Administered Dissociative State Scale, and the State Anxiety Sub-scale of the State–Trait Anxiety Inventory.

PDS (Foa, 1995). The PDS was designed as a self-reportinstrument to assess PTSD using criteria of the Diagnostic andStatistical Manual of Mental Disorders (4th ed.; DSM–IV; Amer-ican Psychiatric Association, 1994). It was administered in thisstudy as a structured interview. Both the presence and severity ofthe 17 DSM–IV PTSD symptoms are measured on a scale rangingfrom 0 (never) to 3 (5 times per week or more/nearly always). ThePDS also assesses types of trauma experienced, as well as DSM–IVcriteria A, E, and F, using tick box and force choice responses.Because the majority of participants reported multiple traumas,questions were anchored to the Troubles-related trauma causingthe most distress. Several studies support the reliability and valid-ity of the scale (e.g., Foa, Cashman, Jaycox, & Perry, 1997). ThePDS also shows good agreement with the Structured ClinicalInterview for PTSD (Foa et al., 1997). Cronbach’s alpha for the17-item PTSD Symptom Severity Scale of the PDS in the currentstudy was .96 (Guttman’s �6 � .98). Additionally, because recentresearch has suggested that the PDS approximates a four-factorstructure, an omega hierarchical coefficient was calculated on thebasis of the structure recommended by Olff, Sijbrandij, Opmeer,Carlier, and Gersons (2009): �h � .75.

Dissociative Experiences Scale (DES; Carlson & Putnam,1993). The DES is a self-report scale containing 28 items mea-suring trait dissociative experiences and symptoms. Respondentsare required to indicate how often they experience each item whennot under the influence of alcohol or drugs. Collectively, eightitems of the DES known as the Dissociative Experiences Scale–Taxon (DES-T) are believed to tap pathological dissociative ten-

2 Although having reported being literate, participants excluded forliteracy reasons were unable to read five or more of the words shownduring the study phase. Following Michael et al. (2005), participants werealso excluded if they were not able to think of a possible word completionfor four or more of the word stems or word-cue associations presentedduring the priming tasks. This was to ensure valid results based on thepriming task’s reliance on language fluency. No participants who success-fully completed the encoding task failed this criterion.

779CHRONIC PTSD, PRIMING, AND DISSOCIATION

dencies (Waller, Putnam, & Carlson, 1996). Responses are mea-sured on a scale ranging from 0 (never) to 100 (always). Overallscores range from 0 to 100, with higher scores indicating higherlevels of dissociation. The DES has been used in well over 200published studies, and its psychometric properties are well attested(van Ijzendoorn & Schuengel, 1996). In the current study, Cron-bach’s alphas for the DES and DES-T were .96 and .89, respec-tively (Guttman’s �6 were .99 and .91).

Brief Symptom Inventory (BSI; Derogatis & Melisaratos,1983). The BSI, a short form of the Symptoms Checklist-90-Revised (Derogatis & Melisaratos, 1983), is designed as a self-report psychological symptoms scale. Each of the 53 items aremeasured on a 5-point scale ranging from 0 (not at all) to 4(extremely). The BSI contains nine primary symptom dimensions,including depression, anxiety, and psychoticism. Higher scores oneach dimension indicate higher levels of symptom experience onthat dimension. This measure allowed a number of variables,including psychoticism and depression, to be controlled in theanalysis, which may distort priming (Michael et al., 2005). Thereliability, validity, and utility of the BSI have been tested in morethan 400 research studies (Derogatis & Melisaratos, 1983). Inthe analyses reported, we made use of the overall mean BSI andthe BSI subscales for depression, anxiety, and psychoticism. Cron-bach’s alpha for these subscales in the current sample were .87,.91, and .67 (Guttman’s �6 were .88, .90, and .66), respectively. Anomega hierarchical reliability coefficient was calculated for overallmean BSI using Schmid-Leiman transformation on an obliquelyrotated nine-factor maximum likelihood factor analysis using the Rsoftware package (Version 2.10.1); �h � .68 (Revelle, 2010;Zinbarg, Yovel, Revelle, & McDonald, 2006).

Clinician-Administered Dissociative State Scale (CADSS;Bremner et al., 1998). The CADSS was developed to assessalterations in levels of state dissociation in a clinical population.The current study omitted the eight observer-rated items, whichhave limited utility (Bremner et al., 1998), and administered the 23self-report items (referred to here as the Dissociation State Scale,or DSS). Item responses are scored on a 5-point scale ranging from0 (not at all) to 4 (extremely). Overall mean scores range from 0to 4, with higher scores indicating higher levels of state dissocia-tion, including the symptom areas depersonalization, derealization,and amnesia (American Psychiatric Association, 1994). TheCADSS self-report items have satisfactory reliability and validity(Bremner et al., 1998). In the current sample, internal consistencywas .94 (Guttman’s �6 approached 1). This measure was includedto assess the degree to which participants experienced state disso-ciation during the experimental tasks.

State Anxiety Inventory (SAI; Spielberger, Gorsuch, &Lushene, 1983). The SAI reflects one half of the State–TraitAnxiety Inventory and contains 20 items measuring current anxi-ety level. Responses to each item range from 1 (not at all) to 4(very much so). Overall scores range from 20 to 80, and the higherthe score, the greater the level of anxiety. This measure wasselected due to its psychometric properties and pragmatic value(Spielberger et al., 1983) and to assess the degree participantsexperienced state anxiety during the experimental tasks. In thepresent sample Cronbach’s alpha for the SAI was .88 (Guttman’s�6 � .94).

Word-Stem Completion and Word-Association Tests

Perceptual priming test. The word-stem completion task is awidely used implicit memory paradigm that tests for perceptualpriming. The task measures priming for previously encoded wordsusing the initial letters (stems) as perceptual retrieval cues. Implicitmemory for encoded words is displayed by completing the stemswith words read during the encoding phase (rather than other morecommon words) and doing so more than do people who have notencoded these words (Graf, Shimamura, & Squire, 1985). Thecurrent study used the new version of the word-stem completiontask (Michael et al., 2005), which includes both target words andmatched neutral words with the same word stem and frequency.This creates a competitive condition between the two memorytraces. Michael et al. (2005) found evidence that this version of thetask offers a more sensitive implicit memory assessment.

Conceptual priming test. The word-cue association task is animplicit memory paradigm that is a test of conceptual priming. Thetask measures priming for previously encoded words using cue-words associated with previously encoded target words as seman-tic retrieval cues. Successful retrieval requires conceptual process-ing. Participants display their implicit memory for encoded wordsby generating more words from the encoding phase in response tocue words (rather than more common associated words) comparedwith people who have not encoded these words (Schacter &McGlynn, 1989).

Initial word list development. Researchers and cliniciansinvolved in the study, along with trainee clinical psychologists,generated words that they associated with (a) Troubles-relatedtrauma themes, (b) general threat themes (disease, deceit, andfinancial loss), and (c) neutral themes (nature and food). In addi-tion, words were collected from local news articles reportingon these themes. These professionals (n � 8) then rated howrelated the words were to their category (Troubles-related words,general threat words, and neutral words) and how emotionallysalient they were on 11-point scales ranging from 0 (not at all) to10 (highly). Scorings were then used to rank words on the basis ofrelatedness to theme and emotional salience (for neutral words,emotional salience ranking was reversed). Words were excluded ifthey were deemed to be related to another group, in order tosignificantly minimize or remove overlap. Defined themes for thegeneral threat and neutral word categories assisted in controllingfor the specific thematic nature of Troubles-related words. Thehighest ranking words were used to generate the final word lists(discussed in the next section).

Word list for the word-stem completion task. Following theprocedure used by Michael et al. (2005), the word-stem comple-tion task word list was comprised of the three different categorygroups, each containing 10 target words: Troubles-related words(e.g., dissident, loyalist, paramilitary), general threat words (e.g.,disease, infectious, debts), and neutral words (e.g., breakfast, sce-nic, peach). For each of the target words, a neutral matched wordwas used with the same frequency and the same initial letters as thetarget word (i.e., the first two letters were the same when the targetword had four letters, and the first three letters were the same whenthe target word had more than four letters). For each matchedword, there was also at least one other word in the Englishlanguage with the same stem that was more frequent. The frequen-cies of the words were taken from the word’s frequency of occur-

780 LYTTLE, DORAHY, HANNA, AND HUNTJENS

rence in the English language as given in the norms of Kucera andFrancis (1967). The mean frequency for each category group wasapproximately 14 per million. No word pair (i.e., target plusmatch) had the same word stem as any other pair. Neutral matchedwords were rated for neutrality by the research team and wereexcluded if deemed not to be neutral. The three groups of wordpairs were divided into two equal sets, half of which made up theperceptual priming word list in Set 1 and half in Set 2. Eachparticipant was presented with one of the two sets during theencoding phase and with the stems for both sets during the testphase. This procedure made it possible to measure whether thewords that were previously encoded had a higher completion ratethan did the words that were not encoded. A three-way analysis ofvariance (ANOVA) was carried out to confirm that no statisticaldifference in word frequencies existed between the different wordcategories (Troubles-related, general threat, and neutral words),word types (target and match words), and the sets within thecategories (Sets 1 and 2). All were far from significant ( p � .9),and no significant interactions were evident. The final word list ispresented in the Appendix.

Word list for the word-cue association task. Again, thethree category groups (Troubles-related, general threat, and neutralwords) were used, this time with each having 10 different targetwords. For each target word, an associated cue word was selected.These cue words were chosen to be moderately associated with thetarget, with a mean association of 4.5 (between the 4th and the 6thassociation) taken from the Edinburgh Associative Thesaurus fromthe MRC Psycholinguistic Database (Wilson, 1988). The words ineach of the three categories were also matched for mean frequencyof use in the English language (Kucera & Francis, 1967). Themean frequency for each category group was approximately 33 permillion. The three groups of target words were divided into twoequal sets, half of which made up the conceptual priming word listin Set 1 and half in Set 2. Each participant was presented with oneof the two sets during the encoding phase and with the entireword-cue associate list for both sets during the test phase. None ofthe words from the word-stem completion word lists were com-monly associated with words on the word-cue association wordlists. In addition, no words on the word association word lists hadthe same stems as did any of the pairs of words on the word-stemcompletion word list. An ANOVA confirmed that no statisticaldifference in word frequencies existed between the different wordcategories and the sets within the categories. An ANOVA alsoconfirmed that no statistical difference in word association valuesexisted between the different word categories and the sets. Thefinal word list is presented in the Appendix.

Final word sets. The words from Set 1 of the word-stemcompletion task word list and Set 1 of the word-cue associationtask word list were placed in a fixed random order. The random-ization was completed with certain conditions, namely that a targetand match pair never appeared consecutively, nor did more thanthree words from one category. Both sets were then combined intoa single word list. The same procedure was carried out to producea single word list with Set 2 word lists.

As a final test of the suitability of the word lists, a pilot study(N � 10) was completed to ensure there were no differences in theaverage times needed to begin reading the words out loud (asrequired in the encoding task). The dependent variable (responsetime) was measured under the influence of word category

(Troubles-related, general threat, and neutral words), word type(target and match words), and set (Sets 1 and 2). A repeated-measures ANOVA failed to produce evidence that any of the threefactors had a significant influence on pronunciation time. Therewere no significant interactions.

Procedure

The study was broken into the following six discrete phases,conducted in a single assessment: (1) administration of the firstportion of the questionnaire battery, (2) word stimuli presentation(encoding phase), (3) 15-min distractor task interval, (4) percep-tual and conceptual retrieval tasks (test phase), (5) free recall task,and (6) administration of the remaining questionnaires, word-rating task, and debriefing. Full written consent was obtainedbefore participation.

Phase 1. Following consent procedures, basic demographicdetails were collected and participants completed the PDS, BSI,and DES verbally in random order.

Phase 2. After a 5-min break, participants completed theencoding task. During the encoding task, half the participants werepresented the complete Set 1 word list and the other half werepresented the complete Set 2 word list. Participants were informedthat they were taking part in a concentration task that investigatedthe effects of trauma on concentration (as in Michael et al., 2005).Participants were not asked to memorize words and were unawarethat their memory would later be tested.

The words were presented individually in a fixed random orderon a 14.1-in. TFT monitor with an adjustable screen (Sony), andthroughout the study participants wore a headset-mounted micro-phone that was attached to a voice key. Before each word, afixation cross appeared for 100 ms followed by the word, whichappeared for 10 s. After 10 s the word flashed away automatically,and following 100 ms a yellow or red dot appeared either below orabove the location where the word had been (both color andposition were random). Participants were asked to read each wordaloud as quickly as possible and then continue concentrating on thescreen until a dot appeared, when they were to call out the dotcolor as quickly and accurately as possible. The dot then flashedaway upon a response on the voice key and the next word ap-peared. Four practice/buffer words were used at the beginning ofthe encoding task ( phoned, cabinet, loudly, able) to accustomparticipants to the use of the computer and prevent a primacyeffect. To prevent a recency effect, three buffer words were pre-sented after the experimental words at the end of the encoding task(temperature, association, mountain). All buffer words were neu-tral and had unique word stems.

Phase 3. Once the encoding task was completed, there was a15-min interval during which participants completed an unrelateddistraction task (i.e., a basic nonverbal matrices task called theMatrix Reasoning subtest; Wechsler, 1991).

Phase 4. After the 15-min distraction task, participants com-pleted the perceptual priming task, followed by the conceptualpriming task (order counterbalanced to control for administrationorder effects). In the perceptual priming task, participants werepresented with all the word stems from both word list sets of theword-stem completion task. Participants were told they were com-pleting a task to see how quickly they could think of a full word tocomplete the stem. No reference was made to the encoding task or

781CHRONIC PTSD, PRIMING, AND DISSOCIATION

memory. Participants were told to complete the stem by calling outas quickly as possible the first word that came to mind thatcorrectly completed the stem. The stem flashed away automati-cally after a response on the voice key, and the next stem appearedafter 2 s. The word stems of the buffer words were presentedbefore and after the experimental words.

In the conceptual priming task, participants were presented withall cue words from both sets of the word-cue association task wordlists. Participants were told they were completing a task to see howquickly they could process information. It was explained that theyhad to concentrate on each word displayed on the screen and thencall out as quickly as possible the first word that the cue wordmade them think of. No reference was made to the encoding taskor memory. Cue words were presented in successive order on thescreen in the same format as the words read during the encodingtask. The cue word flashed away automatically after a response onthe voice key, and the next cue word appeared after 2 s. The bufferwords were presented as cue words before and after the experi-mental words.

Phase 5. Participants then completed a free-recall task, inwhich they were asked to think back to the concentration (encod-ing) task and name as many words as they could remember. Thiswas to assess whether differences in free recall of learned wordswere evident across groups.

Phase 6. Following the experimental tasks, participants com-pleted the DSS and SAI verbally in counterbalanced order. Finallyparticipants were asked to rate how they personally felt about eachof the words they had seen during the encoding task. The scaleranged from �3 (Very Positive) to –3 (Very Negative).

Participants were then debriefed, assessed for level of risk, andinstructed to contact the researcher or their therapist, should par-ticipation leave any residual effects that concerned them. Allassessment was conducted by Nigel Lyttle, a final-year clinicalpsychology graduate student at the time of testing who was notblind to group assignment.

Data Analysis

Scoring of word-stem completions. For each word category,word stems for primed words (i.e., words read during the encodingphase) completed with the exact target word were scored as correct(simple additions to the exact target word, such as pluralization,were marked as correct). The number of correctly completed stemswas then divided by the total number of word stems that couldhave been correctly completed (i.e., 5). This gave the proportion ofcorrectly completed target words. Because participants were pre-sented with the complete set of word stems (i.e., stems from Set 1and Set 2), it was possible to calculate a baseline completion ratefor word stems of target words not seen during the encoding phase(i.e., unprimed). This was scored in the same way as for the primedwords previously mentioned, yielding a proportion score (i.e., totalunprimed word stems completed with unprimed target words di-vided by the total number of unprimed word stems that could havebeen completed with unprimed target words).

Perceptual priming index. The priming score and baselinewere then subtracted to give a perceptual priming index, whichwas the main dependent variable for perceptual priming. Thisindex provides a measure of priming that accounts for the baselinecompletion rate for unprimed word stems.

Scoring of word association completions. The level of con-ceptual priming was calculated in exactly the same way as theperceptual priming. Cue words that were responded to with theexact target words read during the encoding phase were marked ascorrect. The number of correctly completed associations was thendivided by the total number of cue words that could have beencorrectly completed. The unprimed cue words were scored in thesame way as outlined for unprimed word stems.

Conceptual priming index. The priming score and baselinewere then subtracted to give a conceptual priming index, which wasthe main dependent variable for conceptual priming. This index takesinto account the baseline completion rate of unprimed cue words.

Analysis of free-recall test. The number of words correctlyrecalled from the free-recall test was divided by the number ofwords presented in the encoding task to yield a proportion score.

Results

The samples did not significantly differ on age, time sincetrauma, gender, or years of education (see Table 1). The PTSDsample reported significantly higher PTSD symptoms, overallmean BSI scores, depressive symptoms, trait anxiety, psychoti-cism, trait dissociation, and state dissociation. However, groupsdid not differ on state anxiety.

Word Ratings

Participants were asked to rate, on a 7-point scale ranging from–3 (very negative) through 0 (neutral) to � 3 (very positive), howthey explicitly felt about each word they had seen during theencoding phase. Table 2 summarizes these ratings. In terms of theperceptual and conceptual priming lists, both PTSD and non-PTSDparticipants tended to rate Troubles-related words as very negative(�2), which was slightly more negative than general threat words.Neutral words, buffer words, and neutral match words for all wordcategories and sets were on average rated neutral (�0). A mixedANOVA was conducted to examine differences in word ratings forthe perceptual priming word list under the influence of wordcategory (Troubles-related, general threat, neutral), word type (tar-get, match), set (1, 2), and diagnostic group (PTSD, no PTSD). Insupport of the validity of the word list, there was a significant maineffect for category, F(2, 32) � 1.71, p � .001. Troubles-relatedand general threat target words did not differ but were ratedsignificantly more negatively than were neutral target words,t(74) � –8.09, p � .001, and t(74) � –8.15, p � .001, respec-tively. There were no other significant main or interaction effects.The conceptual priming word list rates were also investigated witha mixed ANOVA that examined word ratings under the influenceof word category (Troubles-related, general threat, neutral), set (1,2) and diagnostic group (PTSD, no PTSD). Again, the validity ofthe word list was supported by a significant main effect forcategory, F(2, 33) � 1.94, p � .001. Troubles-related and generalthreat target words did not differ but were rated significantly morenegatively than were neutral target words, t(37) � –18.49, p �.001, and t(37) � –17.55, p � .001, respectively. There were noother main or interaction effects.

Perceptual and Conceptual Priming Effects

The results of the priming tasks are shown in Table 3. In orderto investigate whether differences existed in unprimed baseline

782 LYTTLE, DORAHY, HANNA, AND HUNTJENS

responding, we completed an ANOVA to examine unprimed base-line scores under the influence of Word Category (Troubles-related, general threat, neutral) Priming Task (perceptual, con-ceptual) Diagnostic Group (PTSD, no-PTSD) after covaryingoverall psychopathology with mean BSI scores. Results indicatedthere were no significant main effects or interactions for unprimedbaseline responding. Priming index scores were then examined,and as predicted there was a significant Word Category PrimingTask Diagnostic Group interaction, F(2, 46) � 13.22, p � .001,2 � .37, after covarying overall psychopathology with mean BSIscores. The only other significant effect was a Priming Task Diagnostic Group interaction, F(1, 47) � 6.08, p � .017, 2 � .12,indicating that the PTSD sample showed greater priming on the

perceptual task compared with the conceptual task across catego-ries, whereas the reverse pattern was found for the controls.Separate analyses for each word category with mean BSI as acovariate indicated a significant two-way interaction for PrimingTask Diagnostic Group on Troubles-related words, F(1, 47) �38.79, p � .001, 2 � .45. In the analysis for threat words and theanalysis for neutral words, no significant effects were found.Planned comparisons with mean BSI as a covariate confirmed thatthe PTSD sample showed greater perceptual priming for Troubles-related words than did the comparison sample, F(1, 47) � 19.20,p � .001. Similarly, as predicted, the PTSD group showed lowerconceptual priming for Troubles-related words, F(1, 47) � 14.43,p � .001, than did the comparison sample. Comparable results

Table 1Participants’ Demographics and Trauma Characteristics

Variable PTSD (n � 25) No PTSD (n � 25) t or �2 p

SexMale 17 17Female 8 8

Age t(48) � 0.323 .748Mean years (SD) 43.96 (10.78) 42.80 (14.33)

Education t(48) � �1.27 .210Mean years (SD) 11.42 (1.85) 12.24 (2.65)

Reported primary trauma (n)Paramilitary abduction/hostage 3 3Paramilitary hijacking 1 0Sectariana physical assault 9 8Victims of paramilitary bombings 2 5Paramilitary attacks on the home 3 0Sectariana murder of friend(s)/family member(s) 3 3Victims of sectarian bullying 2 1Sectariana motivated rape 2 0Trauma without direct links to Troubles 0 2b

Time since primary traumac (%) �2(48) � 6.27 .099No trauma 0 12�1 month 0 01–3 months 0 03–6 months 8 06 months to 3 years 4 83–5 years 16 0�5 years 72 80

PDS (PTSD symptom severity) t(48) � 11.03 �.000M (SD) 38.92 (9.30) 9.68 (9.44)

Mean BSI t(48) � 5.21 �.01M (SD) 2.39 (0.70) 1.43 (0.59)

BSI (depression symptom dimension) t(48) � 3.71 �.01M (SD) 15.73 (6.35) 9.52 (5.47)

BSI (anxiety symptom dimension) t(48) � 5.19 �.000M (SD) 15.83 (6.08) 7.04 (5.90)

BSI (psychoticism symptom dimension) t(48) � 4.43 �.000M (SD) 10.19 (4.50) 5.13 (3.51)

DES (trait dissociation) t(30.9) � 4.12 �.000M (SD) 35.63 (24.8) 13.74 (9.50)

DES-T (trait pathological dissociation) t(27.5) � 4.20 �.000M (SD) 30.08 (25.90) 7.54 (7.03)

DSS (postexperimental state dissociation) t(31) � 4.71 �.000M (SD) 0.81 (0.65) 0.15 (0.25)

SAI (postexperimental state anxiety) t(48) � �0.02 .983M (SD) 49.04 (13.00) 49.12 (12.67)

Note. PTSD � posttraumatic stress disorder; PDS � Posttraumatic Stress Diagnostic Scale; BSI � Brief Symptoms Inventory; DES � DissociativeExperiences Scale; DES-T � Dissociative Experiences Scale–Taxon; DSS � Dissociative State Scale; SAI � State Anxiety Inventory.a Sectarian refers to attacks from one political/religious faction against the other. b The primary trauma for these two participants were domestic violenceand childhood sexual abuse. c Primary trauma is the trauma that participants rated as “bothering” them the most at present.

783CHRONIC PTSD, PRIMING, AND DISSOCIATION

were produced when the five participants not exposed to Troubles-related trauma in the control group (see Table 1) were omittedfrom the analyses (three had reported no trauma, and two hadreported index traumas of domestic violence and childhood sexualabuse).

There was a negative correlation between perceptual and con-ceptual priming for Troubles-related words (r � –.28), whichbordered on significance ( p � .053). Finally, in order to assesswhether word set or order of priming test affected results, weconducted an ANOVA to examine the influence of set (1, 2),encoding order (perceptual first, conceptual first), and task order(word stem first, word association first) on perceptual and concep-tual priming for Troubles-related, general threat and neutral words.There were no significant main effects or interactions.

Association Between State and Trait Dissociation andPTSD Severity

State dissociation was strongly correlated with PTSD symptomseverity (r � .70, p � .001). Trait dissociative tendencies (DES)and pathological tendencies (DES-T), were also highly correlatedwith PTSD symptom severity (r � .63 and r � .65, respectively;both ps � .001).

Priming and Dissociation

General dissociative tendency (DES) was highly correlated withstate dissociation (r � .87, p � .001). Correlations betweengeneral dissociative tendencies (DES), state dissociation (DSS),and all priming measures are listed in Table 4. Correlations be-tween general dissociative tendencies and all priming measureswere nonsignificant for both PTSD patients and controls. How-ever, state dissociation showed a significant correlation (r � .40,p � .05) with perceptual priming for Troubles-related words inPTSD participants. All other correlations between dissociation

measures and priming indices were nonsignificant for both PTSDpatients and controls.

Despite the correlation between state dissociation and percep-tual priming for Troubles words in the PTSD group being signif-

Table 3Word-Stem Completion and Word-Cue Association Scores andPriming Index for Participants With and Without PTSD

Priming and wordtype

PTSD No PTSD

M SD M SD

Perceptual priming

Primed wordsTroubles-related .68 .24 .34 .21General threat .27 .22 .37 .24Neutral .18 .16 .32 .15

Unprimed wordsTroubles-related .13 .19 .14 .19General threat .05 .10 .10 .13Neutral .05 .09 .11 .17

Priming indexTroubles-related .55 .23 .17 .20General threat .22 .23 .26 .30Neutral .14 .20 .22 .20

Conceptual priming

Primed wordsTroubles-related .12 .18 .42 .24General threat .30 .28 .42 .26Neutral .21 .25 .37 .23

Unprimed wordsTroubles-related .06 .09 .06 .17General threat .03 .07 .10 .17Neutral .05 .10 .10 .20

Priming indexTroubles-related .06 .18 .37 .28General threat .27 .29 .30 .26Neutral .16 .25 .27 .26

Note. PTSD � posttraumatic stress disorder.

Table 2Average Ratings of Positivity/Negativity of Word List Words forParticipants With and Without PTSD

Word list andword type

PTSD No PTSD

Set 1 Set 2 Set 1 Set 2

Perceptual priming word list

Target wordsTroubles-related �2.54 �2.44 �2.53 �2.78General threat �1.40 �2.22 �1.58 �2.50Neutral 0.48 0.02 0.29 0.23

Match wordsTroubles-related �0.28 0.18 0.44 0.25General threat �0.04 0.02 0.13 �0.03Neutral 0.18 0.08 0.51 �0.08

Buffer words �0.20 �0.11 0.21 �0.03

Conceptual priming word list

Target wordsTroubles-related �2.04 �2.42 �2.20 �2.85General threat �2.04 �2.20 �2.18 �2.68Neutral �0.10 �0.18 0.31 0.00

Note. PTSD � posttraumatic stress disorder.

Table 4Correlation Between Trait and State Dissociation and PrimingIndex for Participants With and Without PTSD

Word type

PTSD No PTSD

DES DSS DES DSS

Perceptual priming

Primed wordsTroubles-related .31 .40� �.26 .22General threat �.19 �.05 �.36 �.03Neutral �.17 �.07 .28 .01

Conceptual priming

Primed wordsTroubles-related .03 �.11 .01 .26General threat .17 �.11 .04 .31Neutral .00 �.15 .00 .25

Note. PTSD � posttraumatic stress disorder; DES � Dissociative Expe-riences Scale; DSS � Dissociative State Scale.� p � .05.

784 LYTTLE, DORAHY, HANNA, AND HUNTJENS

icant (r � –.40), this relationship did not differ from the correla-tion between trait dissociation and perceptual priming forTroubles-related words in this group (r � .31), t(22) � 0.99, p �.33.

To further examine the relationship between type of priming(perceptual and conceptual priming for Troubles-related words)and trait (DES) and state (DSS) dissociation, we conductedrepeated-measures regressions. The DES and DSS were analyzedseparately due to their high correlation (r � .87). In addition, age,years of education, state anxiety, psychoticism, and depressionwere also considered. State dissociation significantly interactedwith type of priming, F(1, 43) � 8.16, p � .007, 2 � .80. Traitdissociation did not significantly interact with type of priming,F(1, 43) � 3.21, p � .08, 2 � .07. In addition, all otherinteractions were nonsignificant.

A hierarchical regression was used to investigate whether statedissociation contributed uniquely to perceptual priming forTroubles-related words when age, years of education, PTSDgroup, state anxiety, psychoticism, and depression were also con-sidered. Trait dissociation was not included in the regressionanalysis, because it correlated highly with state dissociation (r �.87) and therefore created problems of collinearity, and it also didnot significantly interact with priming measures in the repeated-measures regression. The first block consisted of age, years ofeducation, and PTSD group. The second block consisted of psy-choticism and depression. The third block consisted of state dis-sociation and state anxiety, and the final block consisted of theinteraction between the centered state dissociation variable andPTSD group. The results for perceptual priming for Troubles-related words (see Table 5) indicate that in Step 1 only PTSDgroup was significant. In Step 2, there was no significant contri-bution from either psychoticism or depression. In Step 3, impor-tantly, only state dissociation made a significant contribution inpredicting priming for Troubles-related words. There was no in-dication that the interaction between state dissociation and PTSDgroup significantly contributed (see Step 4). Similar results wereproduced when total BSI scores replaced psychoticism and depres-sion in the second block. For conceptual priming, only PTSDgroup turned out to be a significant predictor ( � .57, p � .001;R2 � .34).

Free-Recall Task

Free-recall results are shown in Table 6. There were no signif-icant main effects and no Word Category Priming Task Diagnostic Group interactions, F(2, 47) � 0.22, p � .805.

Discussion

The results replicate and extend the findings of Michael et al.(2005) using a valid manipulation of threat via distinct wordcategories (Troubles-related, general threat, and neutral). As hy-pothesized, evidence of enhanced perceptual priming in PTSD wasfound. Participants with PTSD showed greater perceptual primingfor Troubles-related words (trauma words) in a perceptual primingtask (word-stem completion) than did those without PTSD. Thus,the findings of Michael et al. (2005) appear to generalize from arecently traumatized (�3 months) assault population to a popula-tion with chronic and complex trauma-induced difficulties (seee.g., Dorahy et al., 2009; Dyer et al., 2009). The current study alsoinvestigated the hypothesized lack of conceptual processing andthus conceptual priming in PTSD (Ehlers & Clark, 2000; Roedi-ger, 1990). In line with this hypothesis, PTSD participants showedlower conceptual priming (using a word-cue association task) forTroubles-related words than did those without PTSD. These ef-fects were specific to the Troubles words and not found in generalthreat or neutral words on either task.

The current study also investigated the role of dissociation inperceptual and conceptual priming. Those who reported higherlevels of trait dissociation also reported higher levels of statedissociation during the experimental task. The PTSD patients whoreported higher levels of state dissociation also showed higherperceptual priming for Troubles-related words only. Further inves-tigation of state dissociation and perceptual priming for Troubleswords found that state dissociation made a significant contributionto predicting perceptual priming for these trauma-related words,when age, years of education, and PTSD group and its interactionwith state dissociation, state anxiety, psychoticism, and depressionwere also added into the equation. Thus, the relationship betweenstate dissociation and perceptual priming for Troubles-relatedwords was not better accounted for by variability in state anxiety,psychoticism, or depression.

Table 5Hierarchical Regression Model for Perceptual Priming

Step and variable b SE R2/�R2

Step 1 R2 � .49Age 0.00 0.00 .16Years of education �0.01 0.02 �.05PTSD group �0.38 0.06 �.66���

Step 2 �R2 � .02Psychoticism (BSI) �0.01 0.01 �.17Depression (BSI) 0.01 0.01 .25

Step 3 �R2 � .06State dissociation (DSS) 0.17 0.07 .34�

State anxiety (SAI) 0.00 0.00 .02Step 4 �R2 � .00

PTSD Group State Dissociation �0.03 0.19 �.02

Note. PTSD � posttraumatic stress disorder; BSI � Brief Symptoms Inventory; DSS � Dissociative StateScale; SAI � State Anxiety Inventory.� p � .05. �� p � .01. ��� p � .001.

785CHRONIC PTSD, PRIMING, AND DISSOCIATION

All three markers of dissociation (trait, pathological, and state)were correlated with PTSD symptom severity, supporting thenotion of a strong link between dissociation and PTSD (seeSimeon, 2007). The state dissociation finding in particular sup-ports cross-sectional and longitudinal clinical studies that havefound an association between peritraumatic dissociation and anincreased risk of PTSD (cf. Ozer et al., 2003; Shalev et al., 1996).The state dissociation finding is also consistent with nonclinicalanalogue studies suggesting an association between state dissoci-ation during processing and subsequent analogue PTSD symptom-atology (Holmes et al., 2004). The current results suggest thatdissociation during threat processing may produce perceptual rep-resentations that provide a basis for PTSD reexperiencing symp-toms.

A number of recent studies have suggested the role of schizo-typal personality traits in data-driven processing and developmentof posttraumatic intrusive symptoms. In particular, it has beensuggested that the role of state dissociation and trait dissociation inintrusive symptoms in PTSD may be an artifact of the relationshipbetween these variables and schizotypy (Holmes & Steel, 2004;Steel, Mahmood, & Holmes, 2008). Although the current studywas not designed to directly address this question, the resultssuggest that state dissociation is a better predictor of perceptualpriming for trauma-related words (suggestive of data-driven pro-cessing) than is BSI psychoticism, which assesses positive psy-chosis symptoms.

Yet, if the experience of dissociation during encoding weresimply linked to nonspecific, global data-driven processing, thenone would expect that those with higher levels of state dissociationwould display higher perceptual priming (and lower conceptualpriming) for all stimuli (regardless of schema type or threat val-ance). However, results suggest relatively higher perceptual prim-ing for trauma-related stimuli specifically and point to the role ofdissociation in this process.

Methodological Implications, Strengths, andLimitations

The methodological implications of the current study includereplication of the successful demonstration of an implicit percep-tual memory bias in PTSD using the competitive conditions ver-sion of the word-stem completion task. Current results also provide

evidence of the utility of the word-cue association task in demon-strating an implicit conceptual memory bias in PTSD.

Strengths of the current study include the use of PTSD andcomparison samples drawn from a small geographical area, all ofwhom in the PTSD sample and the majority of whom in thenon-PTSD sample had experienced direct Troubles-related trauma.In addition, all participants had extensive experience of Troubles-related trauma at the community level. The two samples werematched on gender and did not differ in mean age or years ofeducation. It is therefore unlikely that differences in primingeffects are due to differences in relevance of the material ordemographics. Additionally, all participants were in treatment forchronic psychological difficulties. A further strength was the useof word themes developed with other professionals and harvestedfrom the local media. This made it unlikely that differences inpriming effect could be explained by Troubles-related words rep-resenting a more cohesive theme and increased the likelihood thatthe words would be familiar to the entire sample, although this wasnot objectively indexed.

Limitations include the modest number of words within eachword list, meaning the overall number of correct responses wassmall. This was required to keep testing time to an acceptable level(for both participants and the ethical review bodies). BecauseMichael et al. (2005) found comparable results using similarlymodest word lists, the findings appear robust and valid. In addi-tion, it would be preferable that future studies use pre- andpostexperiment measures of state dissociation to allow preciseinvestigation of changes in dissociative state (see Holmes et al.,2004). Also, future studies might include a direct measure oftrauma memory intrusions, in the form of self-report or in apostexperimental diary (see e.g., Wessel, Overwijk, Verwoerd,& de Vrieze, 2008).

The current study was only an indirect test of the perceptualpriming hypothesis of reexperiencing symptoms. This is becausethe study tested priming for words symbolic of the trauma but notthe original stimuli present at the time of the trauma (which wouldbe extremely difficult to do for practical and ethical reasons).Following Michael et al. (2005), the current study argues thatwords, as symbolic stimuli representative of the traumatic experi-ence, are associated in memory with the traumatic event and areassigned similar processing priority. The degree to which wordsare actually symbolic representations of trauma requires furtherinvestigation. It would be preferable that future studies replicatethe current findings using other paradigms that do not rely onwords. The current study cannot conclude with certainty that apure implicit memory effect was observed. However, few wordswere explicitly recalled by participants, and there were no free-recall group differences. This suggests that explicit recall does notexplain the observed results. However, the results do not show thatthere is no explicit memory bias in PTSD, and a number of studiesdo indeed suggest a bias may exist (see e.g., Buckley, Blanchard,& Neill, 2000). Finally, assessments were not conducted blind togroup assignment, creating the possibility of subtle biasing effects.

Summary

In summary, the results replicate and extend the work of Michael etal. (2005), finding further evidence of enhanced perceptual priming inPTSD for trauma stimuli and reduced conceptual priming for the

Table 6Word Recall for Participants With and Without PTSD

Priming and word type

PTSD No PTSD

M SD M SD

Perceptual priming word listTroubles-related .05 .09 .06 .11General threat .03 .09 .05 .10Neutral .01 .04 .04 .10

Conceptual priming word listTroubles-related .04 .08 .02 .07General threat .01 .04 .03 .09Neutral .00 .00 .04 .13

Note. PTSD � posttraumatic stress disorder.

786 LYTTLE, DORAHY, HANNA, AND HUNTJENS

same stimuli. Methodologically the study added further support forthe use of the competitive condition word-stem completion taskand word-cue association task in displaying implicit memory biasin PTSD, which may also have implications for memory biasstudies with other populations. These results are consistent withtheoretical assertions that aberrant memory processes play a sig-nificant role in PTSD (see e.g., Brewin et al., 1996; Ehlers &Clark, 2000; Foa et al., 1989). The current study also found thatstate dissociation made an important contribution to predictingperceptual priming for trauma words.

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Appendix

Word ListsTable A1Word List for the Word-Stem Completion Task

Word type Target word Match word

Troubles wordsSet 1 Beating Beaches

Murderer MurmuredVictim VictorSectarian SecondlyLoyalist Loyalties

Set 2 Perpetrator PerfumeRepublican RepresentedDissident DistractParamilitary ParanormalIntimidation Intimately

General threat wordsSet 1 Fatal Fathers

Surgery SurgedInfectious InformalAbortion AbolishVirus Virtues

Set 2 Nausea NauticalDecay DecidesGerm GearsPuke PuffSick Silence

Neutral wordsSet 1 Breakfast Breath

Scenic ScentedPeach PeacockSquirrel SqueakHumid Humour

Set 2 Countryside CourtyardGrass GrantOrchard OrchidsTidal TidiedEarthworm Earphones

(Appendix continues)

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Table A2Word List for the Word-Cue Association Task

Word type Target word Cue word

Troubles wordsSet 1 Blast Rocket

Riot ChaosViolence ForceBalaclava HelmetCatholic Religious

Set 2 Terror HorrorShooting RiflesBullet SlugExplosion OutburstConflict Strife

General threat wordsSet 1 Cheated Misled

Shame CryingDebts BillsEnemy ArchFailures Attempts

Set 2 Ulcer StomachFever GlandRaw CookedHell AngelsShit Dung

Neutral wordsSet 1 Estate Real

Weight LightKnitting WoolApple JuicePastry Dough

Set 2 Wire ConnectionSauce RadishFence GateHandle JugSoup Vegetable

Received December 5, 2008Revision received June 11, 2010

Accepted June 11, 2010 �

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