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Hearing voices inside and outsidethe head: spatial source monitoringin participants prone to auditoryhallucinationsMeredith McKague a , Ken I. McAnally a , Francis Puccio a , SarahBendall b & Henry J. Jackson a ba Psychological Sciences, University of Melbourne, Parkville,Victoria, Australiab Orygen Youth Health Research Centre, Parkville, Victoria,Australia

Available online: 10 May 2012

To cite this article: Meredith McKague, Ken I. McAnally, Francis Puccio, Sarah Bendall& Henry J. Jackson (2012): Hearing voices inside and outside the head: spatial sourcemonitoring in participants prone to auditory hallucinations, Cognitive Neuropsychiatry,DOI:10.1080/13546805.2012.670503

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Hearing voices inside and outside the head: spatial source

monitoring in participants prone to auditory hallucinations

Meredith McKague1, Ken I. McAnally1, Francis Puccio1,Sarah Bendall2, and Henry J. Jackson1,2

1Psychological Sciences, University of Melbourne, Parkville, Victoria,Australia2Orygen Youth Health Research Centre, Parkville, Victoria, Australia

Introduction. Previous studies of source monitoring and auditory hallucinations(AH) have often conflated spatial source (internal-external) with source agency(self!other). Other studies have used suboptimal manipulations of auditory space(e.g., imagine saying vs. saying aloud). We avoided these problems by presentingexperimenter-generated stimuli over headphones in the voice of another person sothat the location of the voice sounded either internal or external to the participant’shead.Methods. Participants (N"121) studied 96 words and indicated for each whether itwas presented internally or externally (online spatial source monitoring). At test,studied words were presented visually, intermixed randomly with 96 unstudiedwords. Participants indicated whether each item was old or new (item memory) andwhether it was presented internally or externally during study (spatial sourcememory). Independent measures of memory accuracy and response bias werederived for online source monitoring, item memory and source memory usingsignal detection theory. Performance on these measures was compared between twogroups of 30 participants who scored low or high on a measure of AH proneness.Results. ANOVAs revealed no differences between the high- and low-AH groups inonline spatial source monitoring, item memory, or spatial source memory.Conclusions. We found no evidence that proneness to AH in a sample of healthyvolunteers was related to any of the measures of spatial source monitoringperformance. We recommend that the methods introduced be applied to futureinvestigations of spatial source monitoring with patient groups and with individualsat-risk for psychosis.

Keywords: Auditory hallucinations; Continuum hypothesis; Psychosis; Sourcemonitoring; Spatial localisation.

Correspondence should be addressed to Meredith McKague, Psychological Sciences,

University of Melbourne, Parkville, Victoria 3010, Australia. E-mail: mckaguem@unimelb.edu.au

COGNITIVE NEUROPSYCHIATRY

2012, 1!21, iFirst

# 2012 Psychology Press, an imprint of the Taylor & Francis Group, an Informa business

http://www.psypress.com/cogneuropsychiatry http://dx.doi.org/10.1080/13546805.2012.670503

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INTRODUCTION

Auditory hallucinations (AH), including auditory-verbal hallucinations(AVH), are a core positive symptom of psychosis, with estimates indicatingthat they are experienced by 60!74% of patients with schizophrenia (Nayani& David, 1996). AH are also experienced to varying degrees among thegeneral population (Stefanis et al., 2002; Waters, Badcock, &Maybery, 2003)and are associated with the same risk factors that predict psychotic disorder(van Os, Linscott, Myin-Germeys, Delespaul, & Krabbendam, 2009).Therefore, studies investigating the underlying cognitive processes associatedwith hallucination proneness in nonclinical samples may be important forinforming the early detection of psychosis.

AH are phenomenologically heterogeneous and may involve a range ofdifferent sounds including talking, laughing, crying, whispering, singing, andhumming, as well as environmental or elemental sounds such as blowing,rustling, rattling, music, bangs, and clicks (Nayani & David, 1996). Indeed,Nayani and David (1996) reported that 62% of their sample of 100schizophrenic patients with AVH heard other sounds as well as voices. Inaddition to the range of sounds experienced, there is also individualvariation in the location from which the sounds/voices are reported toemanate. Phenomenological studies indicate that patients with AH reporthearing them in specific spatial locations which include internal to thehead, external to the body, or a combination of these locations (Copolov,Trauer, & Mackinnon, 2004; Daalman et al., 2010; Hoffman, Varanko,Gilmore, & Mishara, 2008; Judkins & Slade, 1981; Juninger & Frame, 1985;Nayani & David, 1996). A recent study by Daalman and colleagues (2010),in which healthy individuals with AH were compared to psychotic patientswith AH, found that AH localisation was similar in the two groups.

Nayani and David (1996) suggested that the experience of a specificspatial location for AH/AVH is a core phenomenological characteristic thatdistinguishes them from the experience of normal inner-speech and auditorymental imagery, which are not usually experienced as emanating from aspecific spatial location. Consistent with this, a large-scale phenomenologicalstudy conducted by Stephane, Thuras, Nasrallah, and Georgopoulos (2003)identified spatial location as one of three independent dimensions char-acterising the phenomenological experience of AVH in addition to languagecomplexity and self!other attribution. On the basis of such findings from thephenomenological literature, Larøi and Woodward (2007) emphasised theimportance of disambiguating the dimension of spatial location (where?)from the dimension of agency/personification (who?) in studies investigatingthe cognitive mechanisms underpinning AH/AVH.

One prominent account of the cognitive mechanisms underpinning AH isthat they result from a difficulty monitoring the source of memories (e.g.,

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Bentall, 1990, 2000), where source refers to the set of characteristics thattogether specify the conditions (context) under which a memory wasacquired. Johnson, Hashtroudi, and Lindsay (1993) have proposed aframework where item memory and source memory are two components ofthe episodic memory system. Item memory refers to the ability to recall orrecognise previously presented information (e.g., recognising a word from astudy list), whereas source memory refers to the recollection/activation ofcontextual information associated with a memory, including the spatial,temporal, social, and perceptual characteristics that accompanied an event.Source monitoring refers to the cognitive processes that underlie theattribution of source information to a percept or an activated memory trace.

According to the Johnson et al. (1993) framework, problems with sourcemonitoring could result from two separable cognitive loci; one relating toprocesses underpinning the discrimination of source information, and theother relating to a bias to misattribute source information. Difficultydiscriminating source information in memory may occur either becausethe information was inadequately encoded, or because of problems inretrieval mechanisms. Waters, Badcock, Mitchie, and Maybery (2006) havepresented a model of AH where patients with AH have difficulty inaccurately binding source information to activated memory traces. Thiswould manifest as a general difficulty with discriminating source informa-tion correctly in memory, rather than particular bias towards one type oferror. Evidence consistent with this model has been provided by Keefe,Arnold, Bayen, and Harvey (1999), who reported that a group ofschizophrenic patients with Schneiderian first rank symptoms, includingAH, were less accurate than patients without the target symptoms atdeciding whether they had imagined studied words spoken in their own voiceor by the experimenter, without displaying a particular bias for one responseover the other.

Cognitive bias explanations of source monitoring processes in peopleexperiencing AH have also been popular. In particular, it has been suggestedthat patients with AVH have a specific cognitive bias to misattributeinternally generated words to an external, nonself source. Evidence for this‘‘externalisation bias’’ in patients with AVH was first reported by Bentall,Baker, and Havers (1991), and has since been reported in a number of otherstudies with hallucinating patient groups (e.g., Brebion et al., 2000; Gorman,Amador, Malaspina, & Sharif, 2002; Costafreda, Brebion, Allen, McGuire,& Fu, 2008; Woodward, Menon, & Whitman, 2007). Although the externalmisattribution bias account provides an intuitive explanation for themisattribution of source information pertaining to agency during theexperience of AH (i.e., misattributing a self-generated thought to anotherperson), it is not clear that there should be a specific externalisation bias inrelation to spatial source information. This is because roughly equal

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numbers of patients report internal AH as report external AH (e.g., Copolovet al., 2004; Hoffman et al., 2008).

To date, little attention has been given to the ability to correctly assignspatial location to remembered events, despite the fact that Johnson et al.(1993) explicitly name spatial location as one of the core elements of sourceinformation, and despite the clear relevance of spatial source to the corephenomenal features of AVH. Many previous source monitoring studieshave conflated the spatial and the self!other dimensions, where self isassumed to have an internal location and nonself (other) is assumed to beexternally located. There are only a handful of studies in which an attempthas been made to isolate the spatial dimension from the self!otherdimension. For example, Franck et al. (2000) and Stephane, Kuskowski,McClannahan, Surerus, and Nelson (2010) operationalised internal spatiallocation as the subject silently reading a word (Franck et al., 2000) or asentence (Stephane et al., 2010), while external location was operationalisedas the subject reading aloud (see also Henquet, Krabbendam, Dautzenberg,Jollesa, & Merckelbach, 2005; Rankin & O’Carroll, 1995). Stephane et al.reported that schizophrenic patients had more difficulty than normalcontrols in discriminating words they had read silently from those theyread aloud. Despite the authors referring to the patients’ source memorydeficits as a ‘‘bidirectional bias’’, it is more indicative of a difficulty indiscrimination because misattribution errors were made in both directions(inner-to-outer and outer-to-inner).

The conclusions that can be drawn from studies in which spatial sourcehas been manipulated as a comparison between silent reading versus hearingare limited because they rest on the assumption that people experience silentreading as a fully realised voice inside the head and that they hear their ownovert speech at an external spatial locus. Both assumptions are questionable;it is not really clear where a self-generated voice, be it covert or overt speech,is actually perceived. Similarly, in a study by Keefe et al. (1999), participantsdiscriminated between imagining the experimenter saying a word (internalspatial location) and actually hearing the experimenter saying a word(external spatial location). Once again, it is not entirely clear where imaginedspeech is perceived. Furthermore, the latter study conflates self (imagine)and nonself (hear) generation of the stimuli with spatial location.

In the present study, item memory and spatial source memory werecompared between groups of undergraduate students who were either prone(high-AH group) or not prone (low-AH group) to AH. Proneness to AH wasassessed using the subset of questions from the revised Launay-SladeHallucination Scale (LSHS-R) that relate specifically to the experience ofAH. Crucially, we were able to examine spatial source memory withoutconfounding it with the source of generation (i.e., the self!other dimension).The target words and sentences for the source monitoring task were recorded

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using an acoustic mannequin (see Method section) and presented overheadphones so that they sounded as if they emanated either from within thehead (internal location condition) or from a location external to the right ear(external location condition). The location of the voice near the right earmaps onto the findings of Nayani and David (1996), who found that this wasthe most common external location reported by patients experiencing AH.Spatial source monitoring was assessed both during encoding and retrieval.The encoding and retrieval tasks are referred to throughout as the onlinespatial source monitoring and spatial source memory tasks, respectively.

We also examined the effect of emotional valence on item memory andspatial source monitoring because it has been suggested that emotionallyvalenced materials disrupt the encoding processes that serve to bind sourceinformation to memory items, resulting in increased errors when retrievingsource information (e.g., Johnson, Nolde, & Leonardis, 1996). By extension,it has been argued that the source monitoring problem that is proposed tounderlie the phenomenon of AH should be most apparent for words (andother stimuli) associated with strong emotional valence (Bentall, 1990;Morrison, Haddock, & Tarrier, 1995). In support of this, it has beenreported that the source monitoring performance of schizophrenic patientswith AH is particularly poor for negatively valenced stimuli, relative topatients without AH, at least in tasks assessing the self!other dimension(e.g., Baker & Morrison, 1998; Morrison & Haddock, 1997). Furthermore,Larøi, van der Linden, and Marczewski (2004) provided evidence thatnonpatient participants who scored high on the LSHS-R made more self-to-other source-misattribution errors than those who scored low on theLSHS-R for valenced items.

To examine whether emotional valence also affects spatial sourcemonitoring, we selected half of the target words to have strong positivevalence and half to have strong negative valence. The words in each valencecategory were matched for arousal, word length, word frequency, image-ability, and orthographic regularity and similarity (see Larsen, Mercer, &Balota, 2006, for a discussion of the importance of matching valencedstimuli on linguistic variables).

We analysed our data using signal detection theory (SDT; Green & Swets,1966; Macmillan & Creelman, 2005). SDT is the method of choice formodelling source memory in the cognitive psychology literature (Hautus,Macmillan, & Rotello, 2008; Mitchell & Johnson, 2000) and is considered amore appropriate representation of the cognitive processes underlying sourcememory than the multinomial modelling approach (Broder & Meiser, 2007)that has been used in previous AH/source monitoring studies (e.g., Keefeet al., 1999; Keefe, Arnold, Bayen, McEvoy, & Wilson, 2002). SDT providesa measure of each participant’s ability to discriminate two sources ofinformation, captured in the measure referred to as sensitivity (d?). SDT

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also provides a measure of bias which reflects the extent to which eachparticipant makes more of one type of error than another.

Sensitivity (d?) and bias measures were calculated for each participant foronline source monitoring, for item memory, and for spatial source memory,and served as dependent variables in a series of ANOVAs. The designallowed the following hypotheses to be tested. First, if individuals prone toAH have generally poor recognition memory (i.e., item memory) comparedto those not prone, then the mean item memory d? should be lower for thehigh-AH group than for the low-AH group. Item memory performance wasnot the central focus of the study, but it is important to ensure that anysource memory deficits observed do not simply reflect a generalised deficit inmemory (e.g., Seal, Crowe, & Cheung, 1997). Second, if individuals prone toAH have greater difficulty in encoding spatial source information than thosenot prone, the mean online source monitoring d? should be lower for thehigh-AH group than for the low-AH group. Third, if individuals prone toAH have greater difficulty in retrieving spatial source information than thosenot prone, the mean source memory d? should be lower for the high-AHgroup than for the low-AH group. Given the known heterogeneity in theexperience of AH location, no a priori hypotheses were advanced relating topotential differences between the high- and low-AH groups in biases ofsource encoding or retrieval. Finally, as noted earlier, source encoding andmemory problems experienced by participants prone to AH are predicted tobe most pronounced for negatively valenced stimuli. This would be indicatedby a significant interaction between item valence and AH group in theanalysis of source d? scores.

METHOD

Participants

One hundred and twenty one undergraduate psychology students (33 males,88 females) from the University of Melbourne volunteered in exchange forpartial course credit. The age range of the sample was 17 to 40 years(mean"19.3, SD"3.4). All were administered the LSHS-R to assessproneness to hallucinations. LSHS-R scores varied from 0 to 37 with amean of 15.4. A subset of LSHS-R questions relate to hearing sounds(Questions 2 and 5) or voices (Questions 7, 8, 10, 11, and 12). Responses tothese questions were combined to indicate proneness to AH. The low-AHgroup comprised the 30 participants who scored lowest on these questions.The high-AH group comprised the 30 participants who scored highest onthese questions. The mean LSHS-R score of the high-AH group was 25.0,which is 1.9 lower than the mean (26.9) reported by Levitan, Ward, Catts,and Hemsley (1996) for their sample of 169 psychiatric patients.

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Materials

Launay-Slade Hallucination Scale-Revised (LSHS-R). The LSHS-R(Launay & Slade, 1981) is a self-report questionnaire that consists of 12items measuring proneness to auditory or visual hallucination. Responsesare made on a 5-point Likert scale. The test!retest reliability of the scale hasbeen shown to be acceptable, r".81 (Aleman, Nieuwenstein, Bocker, & deHaan, 1999). The reliability of this sample as measured by Guttman’slambda (Guttman, 1971) was 0.80.

Center for Epidemiologic Studies Depression Scale (CES-D). TheCES-D is a self-report questionnaire that consists of 20 items measuringstate depression over the past week. The items are statements pertaining tomood, somatic complaint, interpersonal and motor functioning. Responsesare made on a 4-point Likert scale. In analogue samples, the internalconsistency reliability estimates have been reported to range from 0.8 to 0.9and test!retest reliability estimates have ranged from 0.4 to 0.7 over a timeperiod from 2.5 weeks to 1 year (Devins et al., 1988; Radloff, 1977). Thereliability of this sample as measured by Guttman’s lambda was 0.90.

Stimuli for the item memory and source memory tasks. The AffectiveNorms for English Words (ANEW) database (Bradley & Lang, 1999) wasused to select 192 words, of which 96 were negatively valenced and 96 werepositively valenced. The ANEW database primarily provides ratings ofvalence and arousal for over 1000 English words. Valence is measured on ascale from 1 to 9, where 1"high negative valence and 9"high positivevalence (5"neutral). Arousal is measured on a scale from 1 to 9, where1"low arousal and 9"high arousal. The mean valence rating was 2.63(SD"0.7) for the negative words and 7.48 (SD"0.7) for the positive words.Both ratings were highly significantly different from neutral: positive,t(95)"39.2, pB.0001; negative, t(95)"33.8, pB.0001. The words in eachvalence category were matched for arousal ratings (positive"5.44,negative"5.60), t(190)"1.47, p".15.

Two matched sublists of 96 words (48 negative valence; 48 positivevalence) served as studied and unstudied items in the memory task,counterbalanced across participants. These sublists were further dividedinto two matched sublists of 48 items (24 negative valence; 24 positivevalence) which served in the internal and external presentation conditions,counterbalanced across participants. The positive and negative valenceditems within each sublist were matched for arousal using the ANEW, and forword frequency, length, number of word neighbours, and imageability usingthe N-Watch database (Davis, 2005). A series of t-tests conducted on themean scores for each of these lexical characteristics showed no significant

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differences between the positive and negative words (all p-values!.28). Thedesign of the experiment enabled every word to act as its own control acrossfour versions, counterbalanced across participants.

A short carrier sentence was devised for each target word to be presentedwith it in the study phase. Care was taken to ensure that the target words didnot appear in any sentence other than the designated carrier sentence. Arecording was made for each word in isolation and another for each word inits sentence context, spoken by a female. The word and sentence stimuli arepresented in the Appendix.

In order to generate stimuli that were perceived externally to the listener,each word and sentence was spoken from a location close to the right ear ofan acoustic mannequin (Head Acoustics HMS II). An acoustic mannequinhas the head and torso of a mannequin and microphones in the ear canals.When stimuli recorded at each ear of the mannequin are presented throughheadphones to a listener, the listener experiences the acoustic environment ofthe mannequin. In order to generate stimuli that were perceived in themiddle of the listener’s head, recordings from the mannequin’s right ear werepresented to both ears of the listener over headphones, thereby removing allbinaural cues to sound location. The level of the stimulus was reduced by 3dB to match the loudness of the external and internal stimuli.

Procedure

Study phase. In the study phase, words were presented aurally overheadphones. Participants were instructed that they would hear 96 words, eachfollowed by a sentence with the word in context. They were informed that halfof the words and sentences would sound as if they were localised inside theirhead (internal presentation) and the other half would sound external to theirheads, specifically as if someone was talking near their right ear (externalpresentation). They were told that internal and external presentations wouldbe presented randomly, and that their task was to try to remember the wordsand their spatial source for a subsequent memory test.

Online spatial source monitoring task. The ability of listeners todiscriminate between spatial sources was measured by asking them toindicate on each study trial the spatial location of the word and sentence.Participants indicated their response by pressing either of two keys on thekeyboard marked ‘‘int’’ (internal) or ‘‘ext’’ (external). Four practice trialspreceded the study task.

Item memory and source memory phase. Immediately after the studyphase, participants completed the memory task, which consisted of 192

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printed words presented individually on a computer screen. Participants wereinstructed that half of the words were from the study phase and that halfwere unstudied, and that these would be presented in random order. Foreach item, participants were first asked to determine whether the word wasold (studied) or new (unstudied). They were then asked to determine thesource of the item as internal or external. Source judgements were made forevery item, including those for which participants had responded as ‘‘new’’,given the possibility that they may have failed to recognise the word from thestudy list. After completing the item and source memory tasks, participantscompleted the LSHS-R and CES-D questionnaires.

Data analysis

d? and bias scores were calculated for the online source monitoring taskperformed during the study phase, and for the item and spatial sourcememory tasks. These measures were compared between low-AH and high-AH groups using ANOVAs.

RESULTS

The composition (mean age, gender ratio, mean CES-D score, mean LSHS-R score, and mean score on LSHS-R items relating to AH) of the low-AHand high-AH groups are presented in Table 1. Age, gender ratio, and CES-Dscore did not differ significantly between groups. As would be expected, theaverage LSHS-R full-scale scores and AH subscale scores differed signifi-cantly between groups.

TABLE 1Characteristics of the low-AH and high-AH groups

Low-AH High-AH Statistic p

Age 20.2 (0.9) 18.8 (0.5) t(58)"1.26 .21

Gender (m/f) 8/22 5/25 x2(1)"0.88 !0.05

CES-D 15.2 (1.8) 18.1 (1.5) t(58)"1.23 .22

AH (LSHS-R subscale) 2.4 (0.3) 13.8 (0.4) t(58)"24.4 B.001

LSHS-R (full scale) 8.1 (0.7) 25.0 (0.8) t(58)"16.1 B.001

Standard errors of the means are shown in parentheses.

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Online spatial source monitoring

Online source monitoring was measured by the ability of participants toclassify each study item as either internal or external immediately after it waspresented. Participants in both groups performed near ceiling on theclassification task (Table 2). This corresponds to an average online sourced? of around 4.5 for both groups. A one-way ANOVA of d? scores with thefactor of group (low-AH, high-AH) revealed no significant effect of group,F(1, 58)"0.38, p".54, partial h2".006.

The average online source bias for both groups was very small and notsignificantly different from zero: low AH, t(29)"1.35, p".19; high-AH,t(29)"0.79, p".43. A one-way ANOVA with the factor of group (low-AH,high-AH) revealed no significant effect of group, F(1, 58)"0.01, p".92,partial h2B.001.

Item memory

Average accuracy, d? and bias measures for item memory of positively andnegatively valenced words are presented in Table 3. Average accuracywas close to 70% correct for both groups and word valences. The averageitem d? was close to 1.2 for positive items and close to 1.1 for negative items.A two-way ANOVA of d? scores with factors of group (low-AH, high-AH)and valence (positive, negative) revealed a marginal effect of valence,F(1, 58)"3.81, p".06, partial h2".06, but no significant effect of group,F(1, 58)"0.05, p".82, partial h2".001, or interaction between thesefactors, F(1, 58)B0.01, p".95, partial h2B.001. The marginal effect ofvalence reflected that item memory d? tended to be higher for positive thanfor negative items in both groups.

For both groups and for both word valences, average item bias was smalland not significantly different from zero, t(29)51.31, p].20. A two-wayANOVA with factors of group (low-AH, high-AH) and valence (positive,negative) revealed a significant effect of valence, F(1, 58)"10.3, p".002,

TABLE 2Online spatial source monitoring performance for low-AH and high-AH groups

Low-AH High-AH

% correct 98.7 (0.1) 98.5 (0.2)

Source d? 4.50 (0.05) 4.47 (0.06)

Source bias 0.02 (0.02) 0.02 (0.03)

Standard errors of the means are shown in parentheses. Positive values of bias indicate as bias

towards reporting source as external.

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partial h2".151, but no significant effect of group, F(1, 58)"0.12, p".73,partial h2".002, or interaction between these factors, F(1, 58)B0.01,p".95, partial h2B.001. The main effect of valence reflected thatparticipants in both groups showed a stronger bias to say ‘‘new’’ for positivethan for negative items.

Spatial source memory

Average accuracy, d? and bias for the source memory task are presented inTable 4. Average accuracy was close to 58% correct for positive items andclose to 55% correct for negative items. For both groups and for both wordvalences, source d? was significantly different from zero, t(29)]2.95,p5.006. A two-way ANOVA of d? scores with factors of group (low-AH,high-AH) and valence (positive, negative) revealed a significant effect ofvalence, F(1, 58)"5.26, p".02, partial h2".083, but no significant effect ofgroup, F(1, 58)"0.06, p".81, partial h2".001, or interaction between thesefactors, F(1, 58)"0.47, p".50, partial h2".008. The main effect of valence

TABLE 3Item memory performance for the low-AH and high-AH groups

Valence Low-AH High-AH

% correct Positive 69.9 (1.7) 69.0 (1.8)

Negative 68.8 (1.7) 68.7 (1.5)

Item d? Positive 1.21 (0.12) 1.17 (0.12)

Negative 1.11 (0.11) 1.08 (0.09)

Item bias Positive 0.07 (0.11) 0.11 (0.08)

Negative #0.02 (0.10) 0.02 (0.07)

Standard errors of the means are shown in parentheses. Positive values of bias indicate as bias

towards reporting items as new.

TABLE 4Spatial source memory performance for the low-AH and high-AH groups

Valence Low AH High AH

% correct Positive 58.8 (1.5) 57.0 (1.8)

negative 54.9 (1.7) 55.1 (1.4)

Source d? Positive 0.48 (0.09) 0.40 (0.11)

Negative 0.28 (0.09) 0.29 (0.10)

Source bias Positive #0.21 (0.08) #0.35 (0.08)

Negative #0.16 (0.06) #0.17 (0.11)

Standard errors of the means are shown in parentheses. Positive values of bias indicate as bias

towards reporting source as external.

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reflected that source d? was significantly higher for positive than for negativeitems for both groups.

Source bias in the low-AH group for positive and negative items wassignificantly different from zero, t(29)]2.48, p5.019, in the direction ofreporting source as internal. Source bias in the high-AH group for positiveitems was significantly different from zero in the same direction, t(29)"4.54,pB.001, whereas that for negative items was not, t(29)"1.60, p".12. A two-way ANOVA with factors of group (low-AH, high-AH) and valence(positive, negative) revealed a marginal effect of valence, F(1, 58)"3.85,p".054, partial h2".062, but no significant effect of group, F(1, 58)"0.53,p".47, partial h2".009, or interaction between these factors, F(1,58)"1.18, p".28, partial h2".020. The marginal effect of valence reflecteda tendency in both groups for the bias towards ‘‘internal’’ responses to bestronger for positive than for negative items.

Given the known heterogeneity of the perceived locations of AH, it ispossible that the high-AH group consisted of a mixture of individuals whohad an internalisation bias and others who had an externalisation bias.However, analysis of the distribution of source memory bias in the high-AHgroup revealed no evidence of two subsamples because the distribution wasnot significantly different from normal, positive items: W(30)".95, p".20;negative items: W(30)".99, p".99.

DISCUSSION

The present study did not show any differences between groups ofparticipants who scored low or high on proneness to AH in their ability todiscriminate the spatial source of auditory stimuli, or in their response biasduring the online encoding task. There was also no difference betweengroups in sensitivity or bias of item memory, or in sensitivity or bias ofspatial source memory. Indeed, all main effects involving participant groupwere small or negligible in size, even though the mean LSHS-R score for theparticipants in the high-AH group was similar to that of the patient groupreported by Levitan et al. (1996). Finally, although there was a marginal orsignificant main effect of word valence in the analyses of both item andsource memory d? and bias, there was no evidence for a differential effect ofvalence on source memory performance as a function of proneness to AH.The effect size for the interaction between group and valence was small ornegligible in all analyses.

The present study manipulated internal versus external spatial location ina manner which is not confounded with the source of generation (self!other). It is possible that effects described in some previous studies ofspatial source monitoring with patient groups may have been modulated by

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the ‘‘generation effect’’ where the cognitive effort associated with thegeneration of material results in better recognition than for material whichis passively heard (e.g., Slamecka & Graf, 1978). For example, the generationeffect may be a confound in the manipulation used by Keefe et al. (1999) inwhich participants were asked to discriminate between hearing the experi-menter say a word (external location) and imagining the experimenter sayinga word (internal location).

Other studies have controlled the source of generation by askingparticipants to either think or say words aloud (e.g., Stephane et al.,2010). However, as discussed previously, the think/say distinction is really amanipulation of covert versus overt speech rather than one of spatiallocation per se. It is also important to note that neither the Keefe et al.(1999) study, nor Stephane et al. (2010) found significant differences in theirmanipulation of spatial source monitoring between patient groups with andwithout AH. Rather, in both studies schizophrenic patients in generalperformed poorly on the source memory task compared to controls. Thus,both the results of the present study and those of studies with patientsprovide little support for the hypothesis that spatial source monitoring andmemory for auditory spatial location underlie the experience of AH.

The present results are also consistent with the findings of Badcock andcolleagues who have investigated source monitoring of multiple externalspatial loci in healthy individuals with or without predisposition to AH(Badcock, Chhabra, Maybery, & Paulik, 2008; Chhabra, Badcock, Maybery,& Leung, 2011). In these studies, listeners completed a memory-binding taskwhere two or four words were presented in different voices from differentexternal locations, followed by a probe that shared the voice and/or locationwith one or more of the study stimuli. Binding was reflected by theadvantage in accuracy and response speed obtained when the probe had thesame location and voice as one of the study items (i.e., intact binding oflocation and voice), compared to when it shared one of these attributes withone source and the other attribute with another (i.e., recombined locationand voice). This advantage was the same for the two groups of listeners whoscored either high or low on an extended version of the LSHS-R. The sourcememory task employed in the present study can also be considered ameasure of binding because successful completion of the task requires thebinding of spatial location (internal or external) and item identity.Consistent with the results of Badcock et al. (2008) and Chhabra et al.(2011), the present study showed no difference in the ability to bind spatialsource information to studied words between groups scoring high or low onLSHS-R questions relating to AH.

One intriguing aspect of this study was the clear dissociation betweenparticipants’ ability to discriminate internal and external spatial locations inonline spatial source monitoring during the study phase and their relative

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difficulty in retrieving this information, just minutes later at test, despiteexplicit instruction to remember spatial source. This fragility of memory forauditory space was apparent for all participants, regardless of AH proneness.It is likely that when acoustic features, such as the speaker’s voice, arematchedacross internal and external conditions as in the present study, memory forspatial location will be poor because there are no opportunities to formdistinct associations between acoustic features and spatial location. It is likelythat memory for the source of generation (who?) is more importantecologically than memory for spatial location (where?). By extension, it maybe that the spatial location at which AH are perceived (internal or external) isof secondary importance to the sense that the experience is not self-generated.Consistent with this possibility, in a companion study in which we examinedagent source memory (self vs. other) using the same set of items, we foundrobust source sensitivity (mean source d? was greater than 2.0) (McKague,McAnally, Skovron, Bendall, & Jackson, 2012).

There are some limitations to the study which constrain the conclusionsthat can be drawn. First, we did not ascertain the location where individualsperceived their AH. This would have allowed specific hypotheses relating tosource bias to be tested (e.g., Stephane et al., 2010). That is, it is possible thatpeople who hear their AH internally may be expected to show a specificsource monitoring and/or memory bias in the direction of misattributingexternally presented internally, and vice versa for those who hear their voicesexternally. Although specific biases might be expected in some cases, itremains unclear what would be predicted for the significant proportion ofpeople who report hearing their voices at both internal and external loci, orfor those who report difficulty in ascertaining the spatial location of theirAVH (Copolov et al., 2004). Presumably, the latter two instances might beexpected to show a generalised problem with spatial discrimination, ratherthan a specific bias towards one kind of error. This issue should beinvestigated in future studies, but we note that Stephane et al. (2010) foundvery little evidence for such specific biases in their study of spatial sourcemonitoring with schizophrenic patients. Furthermore, as reported in ourResults section, when we examined the distribution of source bias scores forour sample of AH-prone participants, we found no evidence for a mixture of‘‘internalisers’’ and ‘‘externalisers’’.

Second, we did not measure predisposition to delusions which mayinfluence source memory performance (e.g., Allen, Freeman, Johns, &McGuire, 2006). Although it would have been ideal to measure delusionalideation in addition to depressive symptoms, we found no differences inspatial source monitoring performance between the two groups that mayhave been caused by delusion proneness, but misattributed to AH proneness.

Third, the target words and sentences for the spatial source monitoringtasks were all spoken in a female voice, but it has been reported that up to

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70% of AVH are heard in a male voice (Nayani & David, 1996). In futurestudies, participants who report AVH could be asked to report the sex of thevoice that they hear, and the sex of the voices used in the spatial sourcemonitoring task could be manipulated factorially to enable the effect ofspeaker sex to be investigated.

An essential component of the continuum hypothesis is that theexpression of psychotic symptoms in clinical and nonclinical populationsis underpinned by common cognitive mechanisms (Badcock & Hugdahl,2011; David, 2010). The results of the present study provide no evidence thatspatial source monitoring problems underlie proneness to AH in the generalpopulation. It would be important to extend the current methodology to at-risk-for-psychosis and clinical samples before conclusions could be drawnabout the existence of a continuum with respect to monitoring and memoryfor auditory spatial source.

Manuscript received 16 March 2011Revised manuscript received 23 February 2012

First Published online May 2012

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APPENDIX: Word (in bold) and sentence stimuli

1. There was an abundance of food at the party.2. She had a strong ambition to perform.3. He was awed by her presence.4. His favourite day of the year is his birthday.5. The bouquet of flowers smelt like cinnamon.6. To be young is to be carefree.7. She felt complete comfort in her new bed.8. She felt completely safe during daylight hours.9. The dove is said to represent harmony.

10. Her mother’s touch was gentle.11. I would like to inspire someone some day.12. Playing the piano is an absolute joy.13. There was lots of laughter at the comedy show.14. He felt loved and cherished.15. He was so gifted and yet so modest.16. I derive great pleasure from hanging out with my friends.17. He was a man of prestige, held in high regard.18. He received a reward of $1000 for winning the tournament.19. I salute you, my dearest friend.20. He thought the waitress was really sexy.21. Each night she wishes upon her favourite star.22. He was very thankful he had a good friend to confide in.23. The team embarked on a triumphant march.24. He came from a very wealthy family.25. He showed his boyfriend lots of affection.26. The smell of food aroused his hunger.27. The bird was very colourful.28. ‘‘Bless you my child’’, the priest said.29. The girl tried to catch the pretty butterfly.30. He ran the race like a true champion.31. The queen’s crown was sparkling gold.32. She had a strong desire to dye her hair red.33. Playing in the snow is fun for the kids.34. The teacher was very impressed with the student’s assignment.35. He paid one dollar for the chocolate.36. She was touched by the kindness of strangers.37. Liberty is a privilege of our society.38. She played a sweet melody on the flute.39. She approached every pursuit with passion.40. He was a very powerful figure.41. She felt safe and protected by her parents.42. They had a romantic dinner on Valentine’s day.43. They lived in a very secure house.44. Her hair felt silky and smooth.45. His profound talent was almost inconceivable.46. The divers recovered a treasure chest on the ocean floor.47. The warmth of her smile was welcoming.48. He liked to consult his wise grandmother for advice.49. I was in agony when I broke my toe.

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50. He is such an arrogant person.51. To betray a friend is a terrible thing.52. She dropped the vase and now it’s broken.53. The cockroach crawled slowly across the bench.54. Inside the tomb lies a corpse.55. He committed a crime and went to prison.56. They say he was possessed by a demon.57. His clothes are always dirty after playing football.58. She was disgusted by his behaviour.59. He is distressed about a difficult exam.60. Execution is a most inhumane practice.61. The food smells really foul.62. The death of his sister caused him profound grief.63. The fish was helpless as the fisherman reeled it in.64. He developed an infection and had to go to the hospital.65. She regarded him as an invader of her privacy.66. I’m too lazy to do my homework.67. The driver of the car was a complete maniac.68. The girls were nasty to each other.69. He didn’t mean to offend her so he apologised.70. What a scornful woman she was.71. Too much alcohol can be toxic.72. He was very upset about failing his exam.73. The mother was very angry with her children for misbehaving.74. He went to prison on assault charges.75. It was blasphemy to take the Lord’s name in vain.76. There was chaos in the classroom.77. After the funeral the coffin was carried to the grave site.78. His friends called him a coward for staying out of the pool.79. The children were very cruel as they teased the new student.80. I detest egotistical people.81. The natural disaster affected many civilians.82. She felt hurt by her disloyal friend.83. He felt enraged by their indifference.84. She was frozen with fear when she heard a window smash.85. They felt overcome with gloom.86. I hate the sound of screaming babies.87. Ignorance causes many of the world’s problems.88. The insult she received was quite uncalled for.89. She put her friend’s coldness down to jealousy.90. Every time I walk through the city I get lost.91. The girl has a morbid fixation.92. The woman is clearly neurotic.93. The boy began to panic when he saw a spider.94. The man chased after the thief but could not catch him.95. He had an ulcer in his mouth.96. The woman reminded the girl of the wicked witch.97. The little kitten was adorable.98. She believed her dead sister was now her guardian angel.99. He was struck by her unparalleled beauty.100. The light was bright and almost blinding.

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101. She was impressed by his charm.102. All he wanted was a big cuddle.103. They are very devoted to their children.104. She strives for excellence, always.105. He looks forward to taking his family on a holiday.106. They built a statue in his honour.107. I’d like to improve my mathematical skills.108. A good joke always breaks the ice.109. He leaned over and gave her a kiss on the cheek.110. They were a lively bunch at the party.111. It was a miracle they survived such a crash.112. I love nothing more than being out and about in nature.113. She is only satisfied with perfection.114. They were proud parents as they watched their son graduate.115. The students were respectful and quiet.116. She was so generous; they called her a saint.117. They like to snuggle up together by the fire.118. The fundraiser was a terrific idea.119. He felt completely at peace with his decision.120. The waterfall was quite a spectacular sight.121. They celebrated that they were alive after the ordeal.122. The sand on the beach was startlingly white.123. They felt nothing but bliss together.124. Their caress was tender.125. The students felt confident that they were well prepared for assessment.126. It was a delight to see the children progressing.127. The actress wore an elegant dress on the red carpet.128. There he stands in full glory.129. He regarded himself as a very honest person.130. She made everyone laugh with her great sense of humour.131. The diamond ring was expensive132. They perverted the course of justice.133. He was a true, charismatic leader.134. The music was magical and moving.135. They consulted the mystic for spiritual advice.136. We each have our own idea of what paradise represents.137. He was thrilled to be given a promotion at work.138. The rainbow appeared after the rain.139. All the world’s riches cannot ensure happiness.140. Doctors vow to do everything possible to save a life.141. The sunlight shone through the window.142. She was very thoughtful to bring everyone a gift.143. He felt he could trust her with his life.144. She was thrilled to win the competition.145. He had a bad stomach ache after eating so much junk food.146. The boy is afraid of dogs.147. The bomb caused a lot of bloodshed.148. The policeman was corrupt.149. He was a heartless criminal through and through.150. She’s so depressed she won’t get out of bed.151. The last thing I want is to disappoint my parents.

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152. The sign on the door read ‘‘please do not disturb’’.153. She feels like a failure as a parent.154. He committed fraud and was incarcerated.155. The defendant was found guilty.156. The boy hit his younger brother.157. She felt like an idiot as they giggled at her.158. The rookie was made to feel inferior by his boss.159. Sometimes I feel like I’m going insane.160. She visited her husband in jail.161. He feels lonely since his wife passed away.162. The body was taken to the morgue.163. The soccer team felt nervous before competing in the finals.164. The pain of loss is greater than that of physical harm.165. Poverty is a huge problem in the world today.166. The robber got away with lots of money.167. Selfish people are not worth knowing.168. I felt very troubled by their political agendas.169. The heroin addict had turned to stealing for drugs.170. He finally admitted he was an alcoholic in need of help.171. The regime was brutal.172. They heard a loud crash and ran outside to see what had happened.173. The force of the impact deformed the car.174. They say the world’s ills are the work of the devil.175. The injuries she sustained caused her great discomfort.176. There are a lot of evil people in the world.177. That was a rather feeble excuse.178. Greed ruins people.179. They say this place is hell on earth.180. She didn’t want to watch another horror film.181. His actions were judged to be immoral.182. The injury looked very serious so he was taken to the hospital.183. The intruder was masked and dressed in black.184. The serial killer was never caught.185. She felt consumed by her misery.186. They called him a murderer for eating meat.187. The words he used were obscene.188. He knew that the poison would take effect within minutes.189. The school rules are very rigid.190. She felt scared walking alone in the dark.191. Torture is a barbaric interrogation technique.192. He seems to be a rather unhappy child.

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