Alterations in theory of mind in patients withschizophrenia and non-psychotic relatives

Introduction

The ability to infer the mental states (beliefs,thoughts and intentions) of others in order topredict and explain their behaviour has beenconceptualized as a �mentalizing� ability or �theoryof mind� (1, 2). Frith (3) has proposed thatalterations in theory of mind underlie specificsymptoms of psychosis, notably delusions of per-secution, delusions of reference, delusions of mis-identification, third-person auditory hallucinations,some aspects of thought disorder, and negativesymptoms. According to Frith, theory of mindskills in people with these experiences developnormally, but are impaired during an acute psy-chotic episode. Subsequent studies by Frith and co-workers have indeed found that patients withpersecutory delusions, thought disorder, or negat-ive symptoms had difficulties performing a hintingtask and a false-belief task, two tasks that aresensitive to alterations in theory of mind, whereaspatients who were symptom-free at the time oftesting, performed normally (4, 5). These observa-tions suggest that mentalizing ability is a state

rather than a trait variable. However, others foundthat the siblings of individuals with a diagnosis ofschizophrenia performed significantly worser thanthe control participants on theory of mind tests (6).These authors suggested that alterations in theoryof mind in people with psychosis represent at leastin part a trait rather than a state factor. However,their sample was very small and statistical resolu-tion limited.

One way to explain findings of alterations intheory of mind in patients and their healthyrelatives is to assume that alterations in theory ofmind are at least in part secondary to neuropsy-chological deficits. Schizophrenia is associated withneuropsychological deficits (7–12), and similar,although reduced, neuropsychological deficitshave also been noted in relatives of patients withschizophrenia (13–18). The relatives may be at riskfor later development of schizophrenia or have anundiagnosed (but genetically related) schizophreniaspectrum personality disorder. Therefore, as agroup, non-schizophrenic relatives will appearless impaired than those with schizophrenia, butpossibly more impaired than unrelated controls

Janssen I, Krabbendam L, Jolles J, van Os J. Alterations in theory ofmind in patients with schizophrenia and non-psychotic relatives.Acta Psychiatr Scand 2003: 108: 110–117.ªBlackwell Munksgaard 2003.

Objective: It has been proposed that alterations in theory of mindunderlie specific symptoms of psychosis. The present study examinedwhether alterations in theory of mind reflect a trait that can be detectedin non-psychotic relatives of patients with schizophrenia.Method: Participants were 43 patients with schizophrenia orschizoaffective disorder, 41 first-degree non-psychotic relatives and 43controls from the general population. Theory of mind was assessedusing a hinting task and a false-belief task.Results: There was a significant association between schizophreniarisk and failure on the hinting task (OR linear trend ¼ 2.01, 95% CI:1.22–3.31), with relatives having intermediate values between patientsand controls. Adjustment for IQ and neuropsychological factorsreduced the association by small amounts. The association betweenschizophrenia risk and failure on the false-belief tasks was notsignificant.Conclusion: Changes in theory of mind are associated withschizophrenia liability. General cognitive ability and neuropsycholo-gical measures seem to mediate only part of this association.

I. Janssen1, L. Krabbendam1,J. Jolles1, Jim van Os1,21Department of Psychiatry and Neuropsychology, azM/Mondriaan/Riagg/RIBW/Vijverdal Academic Centre,EURON, Maastricht University, Maastricht, TheNetherlands and 2Division of Psychological Medicine,Institute of Psychiatry, De Crespigny Park, Denmark Hill,London, UK

Key words: cognition disorders; neuropsychology;schizophrenia; family; risk factors

Prof. J. van Os, Department of Psychiatry and Neuro-psychology, Maastricht University, PO Box 616 (DRT 10),6200 MD Maastricht, The NetherlandsE-mail: j.vanos@sp.unimaas.nl

Accepted for publication January 21, 2003

Acta Psychiatr Scand 2003: 108: 110–117Printed in UK. All rights reserved

Copyright ª Blackwell Munksgaard 2003

ACTA PSYCHIATRICASCANDINAVICAISSN 0001-690X

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(19). It has been suggested that there may be atleast three domains of neuropsychological deficitsin the non-psychotic relatives of patients that arestable over time: auditory attention, verbalmemory and executive functioning (16, 20). Inchildren, theory of mind skills have been associatedwith executive functions in particular (21–24).Some authors have argued that the cognitivechanges in schizophrenia are part of a generalizeddecline (25), but there is evidence that alterationsin theory of mind in schizophrenia cannot beexplained by the effect of IQ decline alone (26, 27).

In the current study therefore, we wished toexamine whether alterations in theory of mindreflect a trait that can be detected in the relatives ofpatients with schizophrenia, independent of gen-eral IQ and neuropsychological functions such asexecutive functions, memory, verbal fluency, speedand attention.

Material and methods

Subjects

The sample has been described in previous publi-cations (17, 28). Initial selection criteria for allcases were a lifetime history of a period ofpsychosis (at least 2 weeks) in clear consciousness,according to the research diagnostic criteria (RDC)(29), or being a first-degree relative of a patientmeeting this criterion. All patients were in remis-sion or in partial remission, defined as not in needof hospital admission or intensive case manage-ment. Inclusion criteria for all participants were:between the ages of 18–55 years, sufficiently fluentin Dutch, and normal results for physical exam-ination. Written informed consent, conformingto the local ethical committee guidelines, wasobtained from all participants.

Patients were recruited from the catchment areaCommunity Mental Health Centre and the out-patient clinic of the catchment area psychiatrichospital. Relatives (free of a lifetime history ofpsychosis) were sampled through participatingpatients or through associations for relatives ofpatients with psychotic illness. Control subjectswere recruited from the general population througha random mailing procedure in the local area. Noneof the controls reported a history of psychosis in afirst-degree relative, and no control used psycho-tropic medication. The present study included 43patients with psychosis, 41 non-psychotic first-degree relatives, and 43 healthy controls withcompleted measures on social cognition, derivedfrom a larger sample of 50 patients, 51 relatives and50 controls. The study population originated from

57 families with at least one patient with psychosis.Of the healthy relatives, there were six mothers, fivefathers, 20 sisters, nine brothers and one son. Of the57 families, 35 families contributed one case or onerelative, 20 contributed at least one case and onerelative, one contributed two and one contributedthree relatives. Patients, relatives and controls wereinterviewed with the expanded version of the BriefPsychiatric Rating Scale (BPRS) (30), the Positiveand Negative Syndromes Scale (PANSS) (31), thePeters et al. Delusions Inventory (PDI – an instru-ment to measure delusional ideation in non-clinicalpopulations) (32), and case note and other historicalmaterial were additionally screened for symptomslisted in the Operational Criteria Checklist forPsychotic Disorder (OCCPI) (33). Where necessary,additional information was derived from interviewswith the responsible medical officer. Based on thecombined information, the computerized programOPCRIT (33) yielded RDC diagnoses. There were34 patients (79%) with a diagnosis of schizophrenia,and nine patients with a diagnosis of schizoaffectivedisorder (21%). In addition, five relatives werediagnosed with major depression. The patients werefrequency-matched with the control subjects on age,sex and educational level (eight-point scale; primaryschool to university degree) (34). The mean totalscore of the patient group on the BPRS was 39.0(SD ¼ 10.1) and on the PDI the mean score was19.3 (SD ¼ 7.3). There were no significant differ-ences between relatives and controls in mean BPRSscore and PDI score (Table 1). The mean age of firstpsychotic symptoms was 22.0 years (SD ¼ 6.0,range 14–41 years); 41 (95.3%) patients wereusing antipsychotic medication, three (7.0%)patients were also using lithium, 14 (32.6%) werealso using benzodiazepines, eight (18.6%) were alsousing antidepressants and five (11.6%) were alsousing anticholinergic medication. Of the relatives,three (7.3%) were using benzodiazepines, and oneof them was also using antidepressants. Current useof illicit drugs was assessed using section I of theComposite International Diagnostic Interview(CIDI; version 1.1) (35). Four patients used mari-huana and one used cocaine on a weekly basis. Tworelatives reported weekly use of marihuana.

Theory of mind tasks

Theory of mind was assessed by two tasks, aso-called first order false-belief task and a hintingtask, translated into Dutch from Corcoran et al.and Frith (4, 5). The false-belief task consisted oftwo stories that were read aloud to the subjects (seeAppendix 1). After the story was read out, twoquestions were asked. The first question could only

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be answered with knowledge of the mental state ofone of the characters (theory of mind question) andreflected that characters� false belief about thesituation. As a measure of comprehension, subjectswere asked a second question about the reality ofthe situation (reality question). This question couldbe answered correctly without the use of mental-izing abilities. The second question also served as ameasure of how well the subject had rememberedthe story. If the subject gave the wrong answer tothe reality question then the answer to the theoryof mind question for that story was ignored inorder to ensure that the measure reflected a deficitin mentalizing rather than mnemonic or compre-hension ability.

The hinting task was devised to test the ability ofsubjects to infer the real intentions behind indirectspeech utterances. The original task comprised 10short passages presenting an interaction betweentwo characters, four of which were used in thepresent study (see Appendix 1). All passages endedwith one of the characters dropping an obvioushint. The subject was then asked what the charac-ter really meant when he/she said this. An appro-priate response given at this stage was given a scoreof two and the next story was read out. If thesubjects failed to give the correct response, an evenmore obvious hint was added to the story. Thesubject was then asked what the character wantsthe other one to do. If a correct response was givenat this stage, the subject was given a score of one. Ifthe subject failed again to give a correct response, ascore of zero was given for that item.

Neuropsychological assessment

The neuropsychological assessment was directed atthe following cognitive domains: attentional span,

episodic memory, verbal fluency, speed and execu-tive functions. As a measure of attentional span,the number of sequences recalled correctly on theDigit Span backwards was used (36). Episodicmemory was assessed by the Auditory VerbalLearning Task (AVLT) (37, 38). Animal namingwas used as a measure of verbal fluency (38). Asmeasures of speed of information processing weused the reading task of the Stroop Color-WordTest (SCWT Card 1) (39) and the number trackingtask of the Concept Shifting Test (CST) (40) whichis a modified version of the Trailmaking Test (41).The Stroop Color-Word Test involves three cardsdisplaying a hundred stimuli each: color names,colored patches, and color names printed inincongruously colored ink. To assess executivefunctions, we used the interference score of theSCWT, and the interference score of the CST(which is comparable with Trailmaking B). Stroopinterference was expressed as the percentage ofextra time needed for Card III, relative to theaverage of the first and second card. Similarly,the interference score of the CST was expressed asthe percentage of extra time needed for thenumber/letter tracking, relative to the average ofthe number and letter version. To obtain a measureof general intelligence, we used the shortened formof a widely used Dutch Intelligence Test, theGroningen Intelligence Test (GIT) (42). This testyields results that are comparable with those of theWechsler Adult Intelligence Scale-Revised (36).Three subtests have proven to yield a goodapproximation of fullscale IQ (42).

Statistical analyses

Statistical analyses were performed using STATA,version 7.0 (43).

Table 1. Summary statistics of participant characteristics

Controls (1) (n ¼ 43) Relatives (2) (n ¼ 41) Patients (3) (n ¼ 43)

Mean SD (range) Mean SD (range) Mean SD (range) F (df 2,124) P Scheff=

Age 34.9 8.8 (21–50) 38.0 11.7 (19–55) 32.1 7.6 (20–48) 4.0 0.020 3 < 2Sex (M/F) 22/21 16/25 24/19 2.51* 0.285Educational level 4.3 1.7 (1–8) 4.1 1.7 (1–7) 3.9 1.4 (1–6) 0.8 0.432IQ 113.2 11.8 (89–139) 116.5 12.5 (86–135) 104.6 13.3 (75–132) 10.1 0.000 3 < 1,2BPRS 25.3 1.5 (24–30) 28.6 5.3 (24–51) 39.0 10.1 (24–73) 48.8 0.000 3 > 1,2PDI 4.4 3.7 (0–15) 5.3 6.6 (0–37) 19.3 7.3 (5–34) 81.2 0.000 3 > 1,2Neuropsychological tests

AVLT total words 54.7 7.1 (35–66) 50.0 9.2 (29–68) 48.4 8.2 (29–64) 6.9 0.001 2,3 < 1SCWT Card 1 (sec) 40.1 5.7 (31.6–62.0) 43.9 8.7 (32.6–69.0) 46.9 9.3 (34.7–88.4) 7.7 0.001 3 > 1SCWT interference 72.2 24.0 (28.4–130.9) 72.7 19.6 (30.3–119.0) 84.2 31.9 (25.6–168.4) 2.94 0.057CST number (sec) 15.8 3.1 (10.6–25.4) 17.5 4.1 (11.2–26.9) 19.1 6.1 (11.5–40.3) 5.6 0.005 3 > 1CST interference 39.7 29.4 ()8.8–100) 52.0 32.9 ()0.4–146.5) 55.4 38.9 ()21.1–158.4) 2.5 0.0851Digit Span backward 7.4 1.9 (3–12) 6.4 1.9 (2–11) 6.0 1.7 (3–11) 6.3 0.002 3 < 1Verbal fluency 25.1 6.0 (10–39) 25.0 6.1 (16–44) 21.2 6.4 (9–37) 5.50 0.005 3 < 2,1

* Chi-square test. AVLT, Auditory Verbal Learning Task; SCWT, Stroop Color-Word Test; CST, Concept Shifting Test.

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Continuous outcome variables measuring theoryof mind were generated for the false-belief tasksand the hinting task separately. Because thesevariables were extremely skewed because of thefact that the great majority of participants per-formed well on the tasks, the variables weredichotomized (score 0 or 1), a score of 0 indicatingthat the subject did not make any error on the task,a score of 1 indicating that the subject made atleast one error. A three-level group variable wasconstructed reflecting risk for schizophreniawith controls (coded 0) at the baseline, relatives(coded 1) in the middle, and patients (coded 2) inthe highest category. Logistic regression was usedto assess and adjust the association between theoryof mind and schizophrenia risk, expressed as thelogistic regression odds ratio. The following a prioriselected confounders of the association betweentheory of mind and schizophrenia risk were inclu-ded in the logistic regression model: age, sex, levelof education (low, medium, high) and IQ. Inaddition, we assessed the effect of controlling forneuropsychological functions (executive functions,memory, verbal fluency, speed and attention) withhigher scores of these variables indicating poorerperformance. In order to examine the effect ofcurrent level of symptoms on the associationbetween schizophrenia risk and theory of mind,the analyses were adjusted for total score on theBPRS and for the score reflecting the positivepsychotic symptoms. Because alterations in theoryof mind in relatives may be mediated by schizo-typal features, additional analyses were performedin which the association between theory of mindand schizophrenia risk were adjusted for PDIscore.

Results

The mean age of the sample was 35.3 years(SD ¼ 9.8). As a group, the patients were some-what younger than the relatives (see Table 1). Thethree groups were well matched in terms of level ofeducation. The patient group had a significantlylower IQ compared with the relatives and thecontrols (see Table 1). One-way analyses of vari-ance indicated significant differences between thegroups on the total score of the AVLT, SCWTCard 1, CST number tracking, the Digit Spanbackward and verbal fluency (see Table 1). Someparticipants could not be assessed with the false-belief task, because the task was not available atthe time of testing. For the false-belief task, datawere available for 34 patients (47% male), 31relatives (42% male) and 42 controls (50% male).For these groups, mean age of the patients was

32.9 (SD 8.0), mean age of the relatives was 40.2(SD 11.3) and mean age of the controls was 34.8(SD 8.9). Other participant characteristics as wellas neuropsychological test results were comparablewith the characteristics of the whole sample. Thenumber of people that failed on the hinting taskwas: 20 in the patient group (46.5%), 10 in therelatives (24.4%) and eight in the control group(18.6%). Six (17.7%) patients failed on the first-order false-belief task, five (16.1%) relatives andthree (7.1%) controls. Regardless of the effect ofdiagnostic group, a positive but statistically impre-cise association was found between performanceon the false-belief task and the hinting task(OR ¼ 1.43, 95% CI 0.45–4.56).

There was a significant association betweenschizophrenia risk (the three-level variable withcontrols coded 0, relatives coded 1 and schizo-phrenia coded 2) and failure on the hinting task(OR linear trend ¼ 2.01, 95% CI: 1.22–3.31)(Table 2). Compared with controls, the chance offailing the hinting tasks was highest for the patientgroup (OR ¼ 3.80, 95% CI: 1.44–10.04), whereasrelatives had an intermediate chance of failing(OR ¼ 1.41, 95% CI: 0.51–3.90), indicating adose–response relationship. Associations betweenfailure on the false-belief task and schizophreniarisk were equally large but not statistically signi-ficant (OR linear trend ¼ 1.61, 95% CI: 0.85–3.04).

Adjusting the association between schizophreniarisk and performance on the hinting task for age, sexand educational level reduced the excess risk by only2% (OR ¼ 1.99, 95% CI: 1.18–3.35), and addi-tional adjustment for IQ reduced the association byaround 6% (OR ¼ 1.95, 95% CI: 1.13–3.35(Table 2). Adjustment for the neuropsychologicalfactors on top of age, sex and educational levelreduced the association by <30%. Adjustment fortotal score on the BPRS did not change the patternof results (see Table 2), nor did adjustment for thescore reflecting the items on positive psychoticsymptoms (OR linear trend ¼ 2.30, 95% CI: 1.26–4.20). Likewise, after adjustment for the total scoreon the PDI, the association between failure on thehinting task and schizophrenia risk remained signi-ficant (OR linear trend ¼ 4.03, 95% CI: 1.84–8.83).

Discussion

The results show that there was a significant dose–response relationship in the association betweenschizophrenia risk and errors on the hinting task,patients having the highest risk, and first-degreerelatives having intermediate values. Controllingfor age, sex and educational level did not reduce

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the association. Adjusting for IQ and neuropsy-chological factors reduced the association by smallamounts. Failure on the false-belief task was alsopositively associated with schizophrenia risk, butnot significantly so.

The current effect sizes may even underestimatethe true extent of the changes in theory of mind inpatients and relatives, because the groups werematched on educational level with the controlgroup. As the onset of schizophrenia may interferewith an educational career, individuals fall short oftheir educational potential, so that adjusting foreducational level may lead to an underestimationof the size of the group differences. A modestversion of the matching fallacy effect has beenreported in non-psychotic relatives (44).

In the present study, many patients performedwell on the first-order false-belief task, whichsuggests that this task was less sensitive in detectingtheory of mind impairments in schizophrenia. Inthe study by Frith and Corcoran (5), performancewas impaired on both first and second-order false-belief task but other studies have indicated thatalterations in theory of mind in schizophrenia aremore pronounced on second-order tasks, in whicha character has a false belief about the belief ofanother character (27). Second-order tasks involvemore sophisticated theory of mind skills than thoseof first order. It is thus possible that significantdeficits on false-belief tasks would have beenapparent in the current study, if we had used asecond-order task. Yet, because of the higherinformation processing demands posed by thistype of false-belief tasks, performance will bepartly determined by general cognitive abilities.Indeed, in the study by Doody et al. (45) learning-disabled individuals performed worse than normalcontrols on a second-order task, indicating that IQdoes influence performance. The individuals with

schizophrenia nonetheless performed markedlyworse compared with the mild learning disabilitiesgroup and with the affective disorder group,suggesting a degree of specificity of poor theoryof mind performance to schizophrenia that cannotbe explained by the effect of IQ alone.

A limitation of the current investigation is thatwe used verbal theory of mind tasks only.Although severe deficits of verbal comprehensionwould have limited performance on each of thecognitive tests, as they all depend on the correctunderstanding of verbal instructions, comprehen-sion skills may be particularly relevant for tasksthat consists of short stories. Yet, other studieshave found that theory of mind deficits inpatients with schizophrenia are independent ofthe pictorial or verbal form of the mode ofanswering (46, 47), which argues against thepossibility that our findings can be ascribed tothe verbal nature of the tasks that we used. Theresults of Sarfati et al. (46, 47) suggested thattasks testing the theory of mind with and withoutverbal material result in comparable conclusions.Differences between both conditions, if present,were slight and consistently pointed to betterperformance in the verbal than in the pictorialcondition. This argues against the possibility thatour findings can be ascribed to the verbal natureof the tasks that we used.

Previous studies have suggested that theory ofmind deficit is a state-dependent deficit that fluc-tuates with symptoms (4, 5, 47). However, thepresent findings concur with data presented byWykes et al. (6) that non-psychotic relatives ofpatients with schizophrenia show subtle changes oftheory of mind, suggesting that the theory of minddeficit is at least in part trait-related. In line withthis, alterations in theory of mind in patients andrelatives were apparently not mediated by the

Table 2. Associations between performance on hinting tasks and schizophrenia risk, adjusted for symptoms and neuropsychological variables

OR (relativesvs. controls) 95% CI P

OR (patientsvs. controls) 95% CI P OR (linear trend)� 95% CI P

OR unadjusted 1.41 0.51–3.90 0.507 3.80 1.44–10.04 0.007 2.01 1.22–3.31 0.006OR* 1.29 0.44–3.80 0.644 3.77 1.38–10.30 0.010 1.99 1.18–3.35 0.010OR* + BPRS 1.22 0.39–3.76 0.735 4.51 1.25–16.20 0.021 2.07 1.05–4.09 0.036OR* + IQ 1.29 0.42–3.98 0.658 3.78 1.32–10.78 0.013 1.95 1.13–3.35 0.016OR* + AVLT 1.21 0.40–3.68 0.733 3.47 1.18–10.23 0.024 1.92 1.10–3.35 0.021OR* + Stroop Card 1 1.14 0.38–3.45 0.816 2.92 0.98–8.70 0.054 1.74 1.00–3.05 0.052OR* + Stroop interference 1.27 0.42–3.82 0.670 3.27 1.22–8.77 0.18 1.84 1.11–3.05 0.019OR* + CST number 1.31 0.44–3.88 0.630 3.96 1.32–11.86 0.014 2.01 1.14–3.57 0.016OR* + CST interference 1.25 0.43–3.70 0.681 3.63 1.30–10.15 0.014 1.95 1.14–3.33 0.014OR* + Digit Span 1.35 0.45–4.11 0.596 4.20 1.31–13.42 0.015 2.09 1.15–3.81 0.016OR* + Verbal fluency 1.35 0.44–4.12 0.594 3.14 1.12–8.76 0.029 1.79 1.06–3.02 0.031

* OR adjusted for age, sex and level of education.� The increase in risk with one unit change in schizophrenia risk.

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presence of symptoms or schizotypal features. Thefact that the association between schizophrenialiability and alterations in theory of mind wasindependent of (subclinical) psychopathology givesfurther support to the notion that changes intheory of mind can be considered trait markers forschizophrenia or endophenotypes (48). Yet, allindividuals with schizophrenia who participated inthe current study were in remission or partialremission with a low level of symptoms. It ispossible that impairments in theory of mindbecome more severe with increasing levels ofsymptoms. Indeed, a recent study showed thatdeficits of theory of mind that were present duringthe acute phase had disappeared during recovery(49). Together with the present findings, this mayimply that subtle deficits of theory of mind that arepart of the vulnerability for the disorder becomemore severe with increasing levels of symptoms.This would mean that alterations in theory of mindcan be considered a mediating vulnerability indi-cator (50).

Group (controls, relatives and patients) was usedas a linear variable of continuous schizophrenialiability. By doing so, it was assumed that thedifference between 0 (controls) and 1 (relatives) isthe same as the difference between 1 and 2 (cases).While there is no formal way of assessing whetherthis assumption is correct, testing linear hypothesesof schizophrenia risk using relatives of patients hasnevertheless been proven a useful and statisticallypowerful way to identify traits that may be markersof familial risk (20, 51, 52). The findings areconsistent with the hypothesis that alterations intheory of mind in schizophrenia reflect, at least inpart, factors associated with the disorder’s geneticbasis or shared environmental effects. Although thenumber of schizophrenia genes is unknown, mostresearchers agree that it is the sum of a number ofgenes and environmental factors that lead to thedisorder (53, 54). If this is true, then it is likely thatthere is a graded disposition to the disorder, suchthat the probability of developing schizophrenia,or showing related neuropsychological impair-ments, increases as the degree of predispositionincreases (55). As first-degree relatives of patientswith schizophrenia presumably carry a greatergenetic risk for the disorder than the generalpopulation, our finding of alterations in theory inmind in relatives is consistent with the multifacto-rial model.

General cognitive ability and neuropsychologi-cal measures of memory, attention, verbal fluencyand executive functions seemed to mediate onlypart of the association between theory of mind andschizophrenia risk. The finding that theory of mind

deficit is independent from executive functions isnot in line with some previous studies. Forexample, executive functions were related totheory of mind abilities in both healthy and hard-to-manage children (23, 56) and in children withautism (21). It has even been argued that executivefunctions and theory of mind are cognitivelydependent skills. Particularly, it has been suggestedthat executive functions allow for the developmentof theory of mind and that executive deficits resultin a secondary deficit in the ability to exert controlover one’s own mental states (24, 56, 57). However,this has been questioned by the publication ofseveral case reports of double dissociationsbetween both functions (58, 59). Executive func-tions comprise several cognitive skills. Specificskills, such as the ability to draw inferences fromnarratives are most likely involved in theory ofmind (60).

According to our findings, susceptibility tointerference, a different aspect of executive func-tions, seems to be of minor importance to theory ofmind.

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Appendix 1

First-order false-belief tasks used in the study (5)

John has five cigarettes left in his packet. He putshis packet on the table and goes out of the room.Meanwhile, Janet comes in and takes one of John’scigarettes and leaves the room without Johnknowing.Theory of mind question: When John comes backfor his cigarettes, how many cigarettes does hethink he has left?Reality question: How many cigarettes are reallyleft in John’s packet?

Mary has a box of chocolates which she puts inher top drawer for safe keeping. A few minutes

laterBurglarBill comes in andasksMary, �Whereareyour chocolates, in the top or the bottom drawer?Mary doesn’t want Bill to find her chocolates.Theory of mind question: In which drawer doesMary say her chocolates are, the bottom or thetop? Why?Reality question: Where are the chocolates really?

The four hinting tasks used in the study (4)

Melissa goes to the bathroom for a shower. Annehas just had a bath. Melissa notices the bath isdirty. She calls upstairs to Anne, �Couldn’t you findthe Ajax, Anne?�Question: What does Melissa really mean when shesays this?(If subject fails to respond or gives wrong answer:)Add: Melissa goes on to say, �You are very lazysometimes, Anne!�Question: What does Melissa want Anne to do?

Gordon goes to the supermarket with his mom.They arrive at the sweet aisle. Gordon says, �Cor!Those treacle toffees look delicious!�Question: What does Gordon really mean when shesays this?(If subject fails to respond or gives wrong answer:)Add: Gordon goes on to say, �I’m hungry mum!�Question: What does Gordon want his mum to do?

Rebecca’s birthday is approaching. She says toher dad, �I love animals, especially dogs!�Question: What does Rebecca really mean whenshe says this?(If subject fails to respond or gives wrong answer:)Add: Rebecca goes on to say, �Will the pet shop beopen on my birthday, dad?�Question: What does Rebecca want her dad to do?

Jessica and Max are playing with a train set.Jessica has the blue train and Max the red one.Jessica says to Max, �I don’t like this train.�Question: What does Jessica really mean when shesays this?(If subject fails to respond or gives wrong answer:)Add: Jessica goes on to say, �Red is my favouritecolour.�Question: What does Jessica want Max to do?

Theory of mind in patients and their relatives

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