Cognitive Development 17 (2002) 1451–1472

Theory of mind finds its Piagetianperspective:why alternative naming comes with

understanding belief

Josef Pernera,∗, Sandra Stummera, Manuel Sprunga,Martin Dohertyb

a Department of Psychology, University of Salzburg, Hellbrunnerstrasse 34,A-5020 Salzburg, Austria

b University of Stirling, Stirling, Scotland, UK

Abstract

In the last of a series of experiments 48 3–5-year old children were tested on an alter-native naming game with “synonyms,” e.g., if puppet calls the depicted item a “rabbit” thechild has to call it a “bunny,” or the child has to judge puppet’s performance when rolesare reversed. The game was also played with categories (rabbit–animal), name/colour(rabbit–black), colour/colour (black–white), and part/part (head–tail). The younger chil-dren (≤3.5 years) had severe problems with “synonyms” and categories (alternative namesfor the items,<10% correct), but not with names and colours, only colours, or only parts(>80% correct). Children’s increasing success with age on the alternative names tasks wasclosely paralleled (.53 ≤ r ≤ .72) by their mastery of the false belief task in which theyhad to predict that a mistaken story character would look for a desired object in the wronglocation. For explaining the synchrony between alternative naming and understandingfalse belief we draw on the Piagetian idea that children come to represent perspective atsome point in their development. To apply this idea to the alternative naming game wedraw on the philosophical discussion about sortals (terms that specify what sort of objectsomething is) creating perspective differences.© 2002 Elsevier Science Inc. All rights reserved.

Keywords:Perspective; Preamble; Egocentrism

∗ Corresponding author. Tel.:+43-662-8044-5124; fax:+43-662-6389-5124.E-mail address:josef.perner@sbg.ac.at (J. Perner).

0885-2014/02/$ – see front matter © 2002 Elsevier Science Inc. All rights reserved.PII: S0885-2014(02)00127-2

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1. A Piagetian preamble

Perspective played a central role for Piaget. Intellectual development con-sisted for him of overcoming one’segocentrismby progressivelydecenteringfrom how the world appears within ones point of view (perspective) to an ob-jective, perspective-independent understanding. For instance, the young infant hasto learn that objects do not go out of existence as they disappear from one’s view.Piaget and Inhelder (1948/1956)also investigated the child’s ability to represent(understand) visual perspective. We make use of the notion of representing (under-standing) perspective to explain an otherwise mysterious developmental relationbetween children’s understanding of false belief and their appreciation of alterna-tive labels for objects in a naming game.

Young children’s problems appear to stem from amutual exclusivity(thateach thing can only have one name) orsingle identityconstraint (Flavell, 1988;Markman, 1989). In order to find a common denominator for understanding mul-tiple identities and understanding false belief we propose that both rest on anunderstanding of perspective. This proposal is in the spirit ofCarey (1985)as acompromise between Piaget’s formulations ofdomain generallogical constraintsdefining developmental stages andmodularism, where each domain of knowledgehas its own developmental schedule (e.g.,Leslie, 1994, for theory of mind).

The difficult step is to show why application of alternative labels to objects cre-ates a perspective difference. We achieve a workable definition of “perspective”with a constructivist conceptual analysis in Piaget’s spirit of decentering. Philo-sophical analyses of alternative object individuation with different labels suggestthe involvement of different perspectives. This allows us to show that both the falsebelief task and the alternative naming game require an understanding of perspec-tive. At the end we discuss how understanding perspective relates to children’smutual exclusivity bias and to classic Piagetian tasks like the class inclusion prob-lem. We start with the empirical part.

2. Alternative naming and false belief

2.1. The original “synonyms” and false belief finding

Doherty (1994)andDoherty and Perner (1998)reported a surprisingly strongand robust developmental synchrony between children’s understanding of falsebelief and their ability to master a “synonyms” task. In thefalse belief taskchildrenare told about Max, who puts his chocolate bar into one location (A) and leaves.In his absence the chocolate is unexpectedly transferred to another location (B).He returns hungry for his chocolate. Children are asked where he will look forthe chocolate. Typically young 3-year-olds answer incorrectly that he will lookin location B where the chocolate bar actually is. After 4 years most childrengive the correct answer that he will look in A (which is empty but where he

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thinks it is). This happens at the same age at which they pass the “synonyms”task.

In the “synonyms” taskchildren were first tested for their knowledge of wordpairs that come close to being synonyms, e.g., bunny–rabbit, lady–woman, tele-vision–TV, etc. On different occasions children were shown the same object amongthree distractors and asked, “Which one is thebunny?” and later, “Which one istherabbit?” In the task proper a speaking puppet named an object, e.g.,rabbit, andchildren had to “help” the puppet provide an alternative name,bunny. The task wasfirst demonstrated with feedback on three modelling pairs. The experimenter pro-vided the answers if the child could not, and explained that the answer, e.g.,bunny,was correct because the object had two names,bunnyandrabbit. Then five testpairs were presented. The pairs were presented twice, once with the puppet provid-ing one of the synonyms, then the other synonym. This was to ensure that childrencould not succeed by using their habitual term. Younger children tended to repeatpuppet’s expression, while most of the older children correctly used the alternativeword on both trials. Performance on the “synonyms” task and the false belief taskcorrelated strongly (r =≥ .65) even with children’s age and verbal intelligencepartialled out (pr≥ .60). Because children had to produce a suitable alternativeexpression, this was called theproductionversion of the “synonyms” task.

The paradigm was also played with reversed roles. The child named the itemfirst (e.g., “a rabbit”) and the puppet then had to produce the alternative expression.The child was to judge whether the puppet had conformed to the instructions ineach of three trial types in a random sequence (judgementversion). The puppeteither (1) correctly used the alternative description (“a bunny,” correct judgement:“yes, puppet said the right thing”), or (2) repeated the child’s label (“a rabbit,”correct judgement: “no”), or (3) said something wrong (“an elephant,” correctjudgement: “no”). Again correctness of judgements was strongly correlated withpassing the false belief task (r ≥ .82, pr ≥ .70). These correlations between thefalse belief task and the judgement version of the synonyms task have since beenreplicated byDoherty (2000), Clements, Heider, Brooks, and Garnham (1998),andGarnham, Brooks, Garnham, and Ostenfeld (2000).

2.2. Competing explanations

Doherty (1994)had designed the “synonyms” task as test of the theory thatchildren’s mastery of the false belief test reflects a deeper understanding of mentalstates as representations (Flavell, 1988; Forguson & Gopnik, 1988; Perner, 1988,1991) and dubbed that theory RUM “RepresentationalUnderstanding ofMind”. Itimplies that children apply their newly gained understanding to beliefs but also toother, non-mental representations.Zaitchik (1990)had explored this expectationin the realm of pictorial representations. The “synonyms” task was designed tocheck this implication for understanding linguistic expressions as representations.It uses the fact that language as a representational medium can have different rep-resentational forms (words) to represent the same content (meaning). To succeed

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on the task children have to pay attention to the sameness of meaning of synonyms(they can’t allow a name that is not a synonym) and at the same time ensure thatthe second label does not have the same form as the first one, i.e., be a synonymand not a repetition of the first label. The data bore out strongly the expectationthat the “synonyms” task and the false belief task are mastered at the same age aspredicted by the theory that they both require an understanding of representation.

An alternative explanation for the data byDoherty and Perner (1998)can bederived from a speculation byFlavell (1988, pp. 245–246)andMarkman (1989,p. 212). They suggested that children’s tendency to assume that each object onlyhas one ‘name’ may have the same origins as children’s inability to understand theappearance–reality distinction (Flavell, Flavell, & Green, 1983) and false belief(Wimmer & Perner, 1983). Mutual exclusivity has been introduced as a princi-ple that helps infants and children map new words to objects (Carey & Bartlett,1978; Dockrell, 1981; Dockrell & Campbell, 1986; Markman & Wachtel, 1988;Merriman & Bowman, 1989). Although, in the “synonyms” tasks children are notlearning new words but have to operate with ostensively familiar words, a kind ofconscious mutual exclusivity constraint could be evoked when children are directlyfaced with the fact that more than one label exists for an object.

An obvious implication of this “ME hypothesis” is that children should not onlyhave problems with “synonyms” but with any two alternative labels for the sameobject, e.g., basic and superordinate category labels: rabbit–animal. In contrast,the representational-understanding-of-mind (RUM) hypothesis would predict thatthis task should be substantially easier than the synonyms task, because “this is arabbit” and “this is an animal” have clearly different meanings and the task can bemastered without understanding “rabbit” and “animal” as pure variations of wordforms (representational vehicle) with constant meaning (representational content).In a series of experiments these differential predictions were put to a test. We brieflysummarise the results of the first three experiments and then report with properdetails the last, most encompassing study.

Stummer (1997, Experiment 2)developed the production version of the“synonyms” task into two different versions ofsay-something-different(SSD)tasks. In thecategoriestask the alternative labels are a basic and a superordinatecategory, i.e., if the puppet calls it “a dog” the child should call it “an animal” andvice versain response to the prompt “Now, say the other thing!”Stummer (2001,Experiment 1)also used a subordinate and basic categories task (e.g., “poodle” vs.“dog”). The “synonyms” and the categories tasks are both name/name (NN) tasks,i.e., if puppet uses one name for the object, the child has to use the other namefor it. Thecolour/name(CN) task was designed as a control condition of similarstructure and complexity as the NN tasks but without the use of alternative names(categories or synonyms). The child is instructed to say the object’s colour if thepuppet had said its name, andvice versa. For instance, if the puppet had said, “it’sblack,” then the child should say, “it’s a dog.” This task should be easier than theother SSD tasks according to both theories. It should be easy according to MEsince the colour of an object does not specify what kind it is, hence there is no dual

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Table 1Results from experiments by Stummer and from the experiment reported here

Tasks Stummer (1997)(3.0–6.1,n = 36)

Stummer (2001)(3.4–4.9,n = 40)

Present experiment(2.8–4.9,n = 2 × 24)

Production Judgement

% Children correct on all itemsFalse belief 61 73 19 19Say-something-different

Synonyms 67 – 38 33Categories 64 73a 42 21Colour/name 94 95 92 87Part/name – – 96 92Colour/colour – – 87 87Part/part – – 92 92

Correlations [with age and verbal intelligence partialled out]FB × synonyms .64∗∗ [.45∗∗] – .66∗∗ [.62∗∗] .72∗∗ [ .72∗∗]FB × categories .59∗∗ [.42∗] .77∗∗ [.65∗∗] .53∗∗ [.25] .60∗∗ [.32]FB × colour/name .38∗ [.32] .37∗ [.20] .13 [−.10] .17 [−.22]FB × part/name – – .11 [.27] .15 [.24]FB × colour/colour – – .17 [.19] .17 [−.08]FB × part/part – – .15 [.18] .15 [.32]

a Average of number of children passing all superordinate/basic tasks and of number passing sub-ordinate/basic tasks.

∗ P ≤ .05.∗∗ P ≤ .01.

identity involved. It should be easy according to RUM since being a dog and beingblack are two different states of affairs. The critical difference between theories isthat according to RUM the categories task should be as easy as the CN task whileaccording to ME it should be as difficult as the “synonyms” task.

The first 2 data columns inTable 1present the results. The upper panel showsthe relative difficulty of the tasks in terms of the percentage of children who passedeach task, which clearly supports the expectations of the ME thesis: the categoriestask and the synonyms task (both alternative naming NN tasks) were of equaldifficulty. The lower panel shows the correlations between tasks confirming theresults ofDoherty (1994)andDoherty and Perner (1998)that the false belief taskrelates strongly to the synonyms (and the categories task) even after differences inage and verbal intelligence have been taken into account.

Stummer (2001, see Perner, Stummer, & Lang, 1999, Table 8.2)also foundthat children had a general tendency to answer with the basic term (e.g., “dog”)regardless of whether the correct alternative was a superordinate (animal) or asubordinate category (poodle). This cannot be interpreted by RUM, which wouldexpect greater difficulty switching from the specific to the more general (e.g.,poodle → dog) since there is no gain in meaning than from the general to themore specific (dog→ poodle) which can be more easily understood in terms of a

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difference in meaning. It does fit, however, the ME hypothesis that children prefera particular term for any one object.

Unfortunately for ME, Stummer’s data with the production paradigm also fitanother plausible explanation that the NN-tasks pose strongerexecutive demandson children than the NC-task. It has been reported that mastery of the FB-task re-lates to improvements in inhibiting prepotent wrong responses (Russell, Mauthner,Sharpe, & Tidswell, 1991) and several other executive tasks (Carlson & Moses,2001; Hughes, Dunn, & White, 1998; for review seePerner & Lang, 1999). Hence,a difference in executive demands provides an explanation for why the NN-tasksare more difficult than the NC-task as well as for why the NN-tasks are masteredat the same time as the FB-task. In particular, the NN tasks have a strong similaritywith the Stroop task, a prototypical executive function task. It is characterised bythe requirement to suppress the more automatised response (e.g.,name the colourdesignated by a colour word) to a request (name the colourof a colour word) inorder to respond with the desired alternative response (name the colourin whichthe colour word is written). The NN-tasks pose the same executive demands. Thereare two (or more) possible responses to the question, “What is this?” and the childhas to suppress the option that comes to mind first, when this option is the wrongone. This is particularly strong when puppet has used the basic term and the childhas to use the super- or subordinate term (as observed byStummer, 2001). It is alsoa problem in the synonyms task because the name just highlighted by puppet (e.g.,“rabbit”) is more likely to come to mind first and needs to be suppressed in order torespond with the other option (“bunny”). In contrast, these executive demands arenot present in the NC-task where the child is instructed to switch between differentquestions. For instance, if puppet answers the question about what the item is, thenthe child has to answer the question about its colour (this task is comparable tothe Stroop control condition of naming the colour in which non-colour words arewritten). We put this hypothesis to test by introducing a colour/colour (CC) anda part/part task (PP). For instance, in the CC task puppet names one of the twocolours of the item and the child has to refrain from repeating the same colour andname the other colour.

Theexecutive demand hypothesispredicts that these tasks should be as difficultas the NN-tasks because they create the same Stroop-like executive demands,i.e., the same request, e.g., “name its colour!” or “name a part of it!” has to beanswered with an alternative possible answer, like in the NN-task. In contrast, theME hypothesispredicts that these new tasks should be as easy as the NC-task,since colour or having a part are not alternative names for the object.

To strengthen the test we also included a judgement version as in the origi-nal study byDoherty and Perner (1998). This also allows us to detect the pos-sibility that executive demands determine children’s performance in conjunc-tion with representational understanding. In that case we expect the NN, CCand PP tasks to be difficult in the production version because they all pose thepresumed executive demands, but only the synonyms task should pose difficul-ties in the judgement version since the judgement version should not pose the

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Stroop type of executive demand. Whereas under the ME hypothesis, only theNN-tasks — but both of them — should pose difficulties in the production as wellas the judgement version.

3. Method

3.1. Participants

Forty-eight children (29 boys, 19 girls) from four nursery schools in Salzburg,Austria participated in this study. Their ages ranged from 2.8 (2 years and 8 months)to 4.9 (mean age of 3.11, S.D. = 7 months).

3.2. Design

Each child was tested in two sessions lasting roughly 15–20 min about 1 weekapart. Each session consisted of four tasks, one standard false belief (FB) task andthree SSD tasks. In one session the FB-task was administered before the SSD tasksand in the other session it was administered after them. Also, in one session theSSD tasks were administered in their production version, and in the other sessionin their judgement version. These factors were fully counter-balanced. For halfof the children in each age group the three SSD tasks were a superordinate/basiccategories task (NN-categories), a name/colour task (NC) and a colour/colour task(CC). For the other half the three tasks were a synonyms task (NN-synonyms), aname/part task (NP) and a part/part task (PP). The order of the three SSD tasks wasfully counter-balanced. The orders of the three trial types of the judgement tasks(puppet responds with same, different or wrong label) were also counter-balanced.A child received a “pass” score for a particular condition if all three trial typeswere answered correctly. For the production versions there were two tasks ineach condition (e.g., superordinate-basic, and basic-superordinate) and a childwas scored as passing if answers for both tasks were correct.

3.3. Materials

The materials for the two false belief tasks were several Playmobile® figures.In the dog storya dog puts his bone in one location and in his absence anotherstory character moves the bone unexpectedly to a new location. Thebook storyfollows the same plot except that a boy Max puts his book in one location and inhis absence his mother moves the book unexpectedly to a new location. Moreover,an extensive battery of memory questions was used at the end:

Memory question 1: Where did he put the bone in the beginning?Reality question: Where is the bone now?Memory question 2: Who put it there?

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The materials for the six SSD-tasks consisted of several A4 sheets with a singleobject depicted on it. A list of all items used for the test-phases in the productionand judgement version of the SSD-tasks is given in theAppendix A.

3.4. Procedure

Each child was tested individually in a small room near the nursery schoolclassrooms. The procedures for the FB-task and the SSD-tasks were modelledafter the study byDoherty and Perner (1998). We only outline the procedure forthe judgement version.

3.4.1. Say-something-different (SSD) tasks — judgement versionFor the vocabulary check 3 A4 sheets were used with four pictures on each. Two

of the pictures were experimental items used later (e.g., train/railway, stool/chair).Children were asked to point to, e.g., a “train” (Zug), and then later to a “railway”(Eisenbahn). The subsequent modelling phase differed for each kind of task. In theNN taskstwo labels were introduced, either two synonyms (“bunny” and “rabbit”)or a basic and a superordinate category (rabbit andanimal). Then the child wasasked what the item was called, and the child used one of the terms, e.g., “rabbit.”It was then explained that the puppet, too, had to say what the item was called butuse a different name, i.e., “bunny.” The puppet shouldn’t say “rabbit,” because thatis what the child had called it. Puppet needs to use a different name, but one thatis right. Puppet couldn’t say “elephant” because this is not an elephant. Puppetneeds to say “bunny” because this is a bunny, and the child had not used “bunny.”Then this game was practised on three trials. On the first trial puppet repeated thesame label the child had used, on the second trial the correct alternative was usedand on the third trial an incorrect term was applied (e.g., “elephant”). Each timethe child was asked: “Did Puppet say what he was supposed to say?1” Each timethe child gave a wrong answer, this was pointed out and the reason for why it waswrong was repeated.

In theNC-taskit was explained that the child can either name the item or saywhat colour it has and that the puppet then had to say the other thing but notsomething that was wrong. In theCC-taskeach object had two colours; childrencould name one of them and puppet was supposed to name the other colour butnot one the object didn’t have. In theNP-taskit was pointed out that the item wasa rabbit and that it had aheadas a part. Then the child was supposed to eithername the item or the part and puppet had to provide the other label, but not onethat didn’t apply. In thePP-tasktwo parts of the item were pointed out (head, tail),the child had to name one of them and puppet the other one but not one the itemdidn’t have. Each task was demonstrated in its three response versions, i.e., the

1 German original: “Hat Rex das gesagt, was er hätte sagen sollen?” NB: We avoided asking whetherit wasright what puppet had said, because “right” might lead children to say “yes” when puppet repeatedthe child’scorrect label.

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puppet wrongly repeating what the child had said, correctly mentioning the otheroption, or incorrectly applying a wrong label.

3.5. Results

3.5.1. False beliefChildren’s answers to the reality control question (Where is the object now?)

were almost perfect (90% were correct in both tasks). They were a little lessreliable in their answers to the two memory control questions: only 65% gavecorrect answers in both tasks. Nevertheless, 30 of the 48 children (62%) answeredall three control questions in both stories correctly, but only 9 of the 48 children(19%) answered both test questions correctly. Since only two children answeredone of the test questions correctly and the other incorrectly, the retest reliability(κ = .874,P < .001) of test question answers was very good.

3.5.2. Say-something-differentChildren were almost perfect in the vocabulary check (96% correct). The per-

centage of children who passed both tasks of the test phase is shown inTable 1(upper panel fourth and fifth column). Children’s problems are restricted to the twoNN-tasks with either synonyms or super-basic categories. There was no differencebetween the group with synonyms and the group with categories, neither in theproduction version:χ2(1, N = 48) = .09,P > .76, nor in the judgement version:χ2(1, N = 48) = .95, P > .33. Although the higher percentages in column 4than in column 5 indicate, in particular for the synonyms task, that more childrenpassed the production task than the judgement version; the difference is, however,not statistically significant (binomial test:n = 8, k = 1, P > .05).

The remaining percentages inTable 1show that children did exceedingly well onall the other SSD-tasks (NC, NP, CC, and PP). There was no significant differencein difficulty between them. There was no difference between the group being testedon colour and the group being tested with parts:�2(1, N = 48) = .36,P > .55,for NC versus NP in the production version, andχ2(1, N = 48) = .22,P > .63,in the judgement version, andχ2(1, N = 48) = .22,P > .63, for CC versus PPin the production version, andχ2(1, N = 48) = .22,P > .63, in the judgementversion. Also, children did no better on the tasks with names (NC or NP) thanon tasks without names (CC or PP): McNemarχ2(1, N = 48) = 1.0, P > .62,for the production version and McNemarχ2(1, N = 48) = .00,P > .99, in thejudgement version.

Fig. 1 shows the developmental trend on these groups of SSD-tasks and theFB-tasks by splitting the group of children into three age groups. It makes clearthat even the youngest children performed close to ceiling on all SSD-tasks excepton the ones that involved dual naming (NN-tasks). On these tasks a strong develop-mental improvement was apparent that paralleled the usual improvement found onthe FB-task in this age range (Wellman, Cross, & Watson, 2001). There was signif-icant improvement with age on all three tasks:χ2(2, N = 48) = 9.76,P < .005,

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Fig. 1. Percentage of children in the three age groups passing each experimental condition.

for NN-production,χ2(2, N = 48) = 6.85, P < .01, for NN-judgement, andχ2(2, N = 48) = 11,P < .01, for FB.

The correlation coefficients in the lower panel ofTable 1(columns 4 and 5) showthe NN-tasks and the FB-task also correlate very strongly with each other. Thesecorrelations remain robust for synonyms even when age and verbal intelligence(K-ABC) are partialled out (numbers in square brackets).

The essence of the results stays the same when the analysis is reduced to thosechildren who answered all control questions correctly. Of these children 20%passed the FB-task, 23% the NN-judgement and 37% the NN-production task and97% all of the other SSD-tasks in the judgement version and 100% all of the otherSSD-tasks in the production version. The difference between NN-tasks and otherSSD-tasks was significant for both production (McNemar’sχ2(1, N = 30) = 19,P < .001) and judgement versions (McNemar’sχ2(1, N = 30) = 22,P < .001).The correlation between FB- and the NN-judgement task is thenr = .71, P <

.001, [pr = .67, P < .001, with age and verbal intelligence partialled out], andbetween FB and the NN-production taskr = .66,P < .001, [pr= .58,P < .005].

3.6. Discussion

The results are exactly as predicted from the ME hypothesis: both NN-tasks,synonyms as well as categories (both involve alternative labels for an object), are

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as difficult as the false belief task in their production as well as the judgementversion. All other SSD-tasks are equally easy.

The massive difference between children’s performance on the NN-tasks andthe other SSD-tasks speaks clearly against the executive demand hypothesis. It alsomakes our results difficult to explain by other potential alternatives, for instance,the CCC theory (cognitivecomplexity andcontrol theory,Zelazo & Frye, 1997).The core claim is that children around 4 years old come to master embedded con-ditionals, and the false belief task has this logical structure (Frye, Zelazo, & Palfai,1995; though seePerner, Stummer, & Lang, 1999, for reservations about how thisanalysis applies to the FB-task). The same analysis could be brought to bear on theSSD tasks (Perner et al., 1999). This could explain why the NN-tasks are masteredat the same time as the FB-task. However, it is difficult to see how it could accountfor the fact that the other SSD tasks are substantially easier, since their logicalstructure seems identical. Similar problems arise for so-called “neo-Piagetian”theories (Case, 1985; Pascual-Leone, 1970) or other theories that argue with de-velopmental changes in working-memory limitations, because it is difficult to seehow the different SSD tasks could pose different working-memory loads.

In sum, the data from this experiment confirm the problems for RUM theory,and they also speak against the executive demands hypothesis and other potentialalternatives. This leaves the ME hypothesis as the only viable alternative for ex-plaining children’s difficulty with the NN-tasks. However, we need to look againat the reasons, why the ME constraint — the reluctance to accept more than onelabel for an object — should be related to the inability to understand belief.

4. Problems with Flavell’s and Markman’s “single identity” hypothesis

Although the data on the SSD-tasks clearly speak for the ME hypothesis, thequestion remains why ME should be developmentally related to failure of under-standing visual perspective, the appearance–reality distinction and — in our case —false belief.Markman (1989)suggested that ME operates not at the level of linguis-tic labels but results from deeper principles of categorisation, namely that “childrenmay believe that an object has one and only one identity — that it can be only onekind of thing. . . .” (Markman, 1989, p. 212). Flavell suggested that the “single iden-tity hypothesis” might also explain children’s problems with appearance–realityproblems where, e.g., a piece of sponge appears to be a rock. “Children of thisage also believe. . . that each object or event in the world has only one nature —one ‘way that it is’ — at any given point in time. It cannot be two or more verydifferent, mutually contradictory, and incompatible things at the same time; rather,it can only be one thing. Consequently, it makes no sense to them to hear some-thing described as being radically different than the single way it ‘is’ (with ‘is’ notdifferentiated from ‘seems to them at that moment’)” (Flavell, 1988, p. 245).

It remains far from clear how the “single identity” hypothesis is to be appliedto the false belief task. It raises the question about which object or event has only

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one nature. One might suggest theobject’s locationas a candidate event. Indeed,this location is given two different labels, e.g., “drawer” (in the false belief) and“cupboard” (in reality). However, there are several problems with this analysis. Oneis children’s surprisingly early competence in pretence (e.g.,Harris & Kavanaugh,1993) where children as young as 2.5 years have little problems pretending thata block (in reality) is a soap bar (in pretence). So why can they understand dualidentity (block–soap) in this case but not in the belief task?

Another problem regards Flavell’s characterisation of what children fail to un-derstand: “It cannot be two or more very different, mutually contradictory, andincompatible things at the same time.” This doesn’t apply as an explanation tothe false belief task (or the appearance–reality distinction), because children arenot required to understand that the object’s location can be thedrawer and thecupboardat the same time. And it doesn’t apply to the NN-tasks because beinga rabbit and being ananimalare not mutually contradictory. Rather, the questionto be answered about ME is not how children manage to understand that a thing(object or event) can be two incompatible things but why children treat compatible(e.g.,rabbit,animal) as incompatible. To answer this question we look at children’sunderstanding of perspective as a common denominator for their problems withfalse belief and their tendency to show ME. Before we can achieve this we needto get clear on what we mean by “perspective.”

5. What is aperspective?

The Concise Oxford English Dictionary (Thompson, 1995) gives three relevantdefinitions:

(1) the art of drawing solid objects. . . so as to give the right impression of relativepositions, size, etc.; (2) the apparent relation between visible objects as to position,distance, etc.; (3) a mental view of the relative importance of things (keep the rightperspective).

Generalising these definitions in representational terms we might say that a dif-ference in perspective occurs whenever there is a difference in content betweendifferent representationsof a particular thing(an object, a scene or an event).

Three aspects are critical for a difference in perspective. (1) There must besome difference and incompatibility (e.g., different apparent relations). (2) Thedifference has to do with how the target is represented (representational aspect).(3) Despite their difference the representations must pertain, in some sense, to thesame target (one and the same ‘thing’that is represented). We only face a differencein visual perspective if we are looking at the same group of objects from differentvantage points, not if we were looking at totally different objects. Or the wordchosen forit only gives a different perspective from another word chosen forit,if the “it” refers to the same ‘thing’ in both cases (conceptual perspective taking,Clark, 1997; Tomasello, 1999).

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It seems clear how this applies to visual perspective differences and to falsebeliefs. If we face each other and between us on a line are a tree and a rockthen I see the tree in front of the rock while you see it behind the rock. Our twocorresponding statements “tree in front of rock,” and “tree behind the rock” areincompatiblein the sense that one of us could not sincerely utter both of them.Our two statements are apparently about thesame target, i.e., the same two objectsand their relative spatial relation between them. Finally, to make sense of what isgoing on we need to refer to our different points of view (representational aspect).Similarly for false belief, our knowledge of where the chocolate really is (chocolatein location B) and Max’s claim that it is still in A are clearlyincompatible, they areabout thesame target(the real location of the chocolate), and to make sense of themwe have to identify Max’s claim as one of a false belief (representational aspect).

Now for an example that we would not call a perspective difference. We arelooking at a Dalmation. I say, “It is beautifully spotted” and you say, “It is a dog.”Does this involve a perspective difference? It involves alternative representations(descriptions) but there is no incompatibility, as I can immediately take your state-ment on board and say, “It is a dog and it is beautifully spotted.” It also brings outa problem in deciding sameness of target. If we consider the dog as the target, thenwe are speaking about the same target, but if we define the target in a more finegrained way then you are speaking aboutits nature, and I aboutits colouring.

But now to the critical issue: What if you call it a dog and I a Dalmatian? Severalauthors assume that this creates a difference in perspective: in each conversation,it is said, we develop a particular conceptual perspective on the world, one ofthe central aspects of language acquisition (Tomasello, 1999). The most typicalexamples involve “multiple identity,” e.g., describing a dog as aDalmatian, dog, oranimal (Clark, 1997). Does such alternative naming create different perspectivesaccording to our criteria? To see that it does we need to go more deeply into whatwe do when we label objects.

5.1. Multiple identity

By using different words to say what somethingis, we do not primarily predi-cate different properties to something but we apply alternative sortals (words thatdetermine what sort of thing something is) and thereby individuate the very thingwe are talking about in different ways (e.g.,Hirsch, 1982). A classical examplethat brings out the problems created by the use of different sortals is the case ofthe statue made of clay (e.g.,Perry, 1970). Let’s say you gave me a piece of claylast week, which an artist friend of mine turned into a lovely statue yesterday. Nowwhen faced with the statue I can individuate it asa piece of clay(the piece I gotfrom you last week) or asa statue(the one made yesterday by my friend). On firstblush and by normal intuition it seems that we have a single object that is a pieceof clay as well as a statue — just like it islengthy and brownish. However, this isnot so straightforward. When asked since when I have been in possession ofit, theanswer depends on what sortal I used to individuateit. If I used “piece of clay”

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the answer is “last week,” if I used “statue” the answer is “yesterday.” So, herewe have our incompatibility resulting from alternative individuation by differentlabels (sortals).

One attempt at explaining what is going on is to assume that there are actuallytwo different things in existence, a piece of clay and a statue that temporallyoverlap, i.e., a part of the temporal ‘stage’ of the piece of clay and the ‘stage’ ofexistence of the statue are identical (e.g.,Perry, 1970). In that case, there would notbe a difference in perspective involved, since the seemingly incompatible answersabout ‘its’ existence are not incompatible after all, because “it” refers to differentthings. However, the question remains, is that just a philosopher’s way out of aquandary or do we actually think that way (despite our conscious denial of it)?

We see, the question whether two representations have the same target or dif-ferent targets and also the question whether their contents are incompatible ornot, are sometimes difficult to answer. To see where the difficulty lies we need todistinguish two different types of perspective difference.

6. Two types of perspective and the “same thing” problem

6.1. Truth-incompatible perspectives

False beliefs (the chocolate is in location A)vis-à-visreality (the chocolate is inB) are clear cases of a difference between truth-incompatible perspectives. That’swhy these beliefs are calledfalse. Similarly, that is why deceptive appearances,e.g., the piece of sponge appears to be a rock, are calleddeceptive, because theappearance misspecifies reality. In these cases it is clear that, e.g., Max’s mistakenstatement, “the chocolate is in A,” and the child’s knowledge, “the chocolate isin B,” have the same target, namely the actual location of the chocolate, althoughMax’s belief misrepresents that target. In case of doubt about what the targetprecisely is, one can define it asthat against which the truth of the propositions,“the chocolate is in A,” and, “the chocolate is in B,”have to be evaluated, i.e.,where the chocolate really is. No such clear criterion for determining the target isavailable for truth-compatible perspectives.

6.2. Truth-compatible perspectives

Visual perspectives and conceptual perspectives are prime examples of thisclass. They share the feature that alternative perspectives are true. For instance,spatial descriptions given from different vantage points like, “A is in front of B,”and “A is behind B,” cannot both be uttered by the same person, “A is in frontof B and A is behind B,” hence there is some incompatibility, but if uttered fromdifferent vantage points neither speaker can be excused of being wrong, i.e., bothstatements are true. Similarly in the case of applying alternative sortals to one andthe same entity: if the statements, “This is astatue,” and “this is apiece of clay,”

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create different perspectives, as some would argue (e.g.,Clark, 1997; Tomasello,1999), then they are truth-compatible perspectives, since statements conforming toeither perspective, e.g., “I have it since yesterday,” and “I have it since last week,”are both true.

The problem with a single target is now the following. Although at face value,“A is in front of B” and “A is behind B” are incompatible, they cannot be incom-patible in some absolute sense, or else they could not both be true. Two solutionsto this puzzle are possible. Either there is a hidden difference in target, and theyare only superficially incompatible, or they have the same target (the spatial rela-tion between A and B) but their descriptors are applicable only within differentframes of reference(Kutschera, 1999, suggested that solution for the dual identityproblem) and are incompatible within a particular frame of reference. We adopt aconstructivist approach to deciding which option to take.

7. A constructivist definition of perspective

At the starting point we use a technical trick and assume all representationsare representations of the same ‘thing:’ thelogical universe(the set of all possibleworlds). That means that any two representations with different content are differ-ent perspectives on the universe. For instance, both of us look at the same Dalmatianand one of us forms the thought, “it is a dog,” and the other, “it is perfectly spotted.”But there is no need, yet, to speak of different perspectives, if we can give the uni-verse more structure (construct parts). That this is easily possible shows in the factthat our two thoughts can be easily integrated within a single thought, “it is a dogAND it is perfectly spotted,” or even, “it is a perfectly spotted dog.” In other casesthis integration requires more construction. The two statements, “It is cold andraining” (spoken in Salzburg) and, “it is hot and sunny,” (spoken in Philadelphia)seem incompatible until we realise that they refer to different parts of the world.One describes the weather in Salzburg, the other the weather in Philadelphia. Con-sequently, they can be uttered by a single person making the difference in targetexplicit: “It is cold and rainingin Salzburgand it is hot and sunnyin Philadelphia.”

Similar cases with a hidden difference in target are often found when peoplerefer to different times or different worlds. If you say, “Santa Claus doesn’t exist”and I, “Santa Claus lives near the North Pole,” we do not need to construe this asdifferent perspectives on a single universe, but we can understand it as talk aboutdifferent worlds, thereal world in which Santa Claus does not exist and afictionalworld in which he is known to live near the North Pole. Evidently, our construc-tive powers to integrate different mental contents as stemming from a coherentlogical universe with different parts (different worlds) are considerable. Adopt-ing Piaget and Inhelder’s (1941/1974, p. 87)language for describing intellectualdevelopment: we progress beyond a flow of independent perspectives (egocen-tric phenomenalism) by discovering properties of the logical universe (world) asobjective co-ordinations among these perspectives.

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But there comes a point where we do not have the conceptual structures to findsuch a solution for integrating seemingly incompatible contents. Spatial perspec-tives are the classic case. “A is in front of B” and “A is behind B” cannot be simplyintegrated by making a hidden difference in target explicit, e.g., “A is in front ofB and A is behind B ” The only common sense way of filling in themissing parts is with a representational reference to different frames of referenceor points of view, e.g., from my/your point of view, from where I am/you are, etc.That is, our only natural way of understanding the relationship between the twostatements is to interpret them as pertaining to different perspectives (points ofview, frames of reference).

8. Children’s mastery of perspective taking

We need to make an important distinction between different levels of“perspective taking:”switching perspectives(taking different perspectives at dif-ferent times) andconfronting perspectives(representing two perspectives simulta-neously; understanding that there are different perspectives). In line withClark’s(1997)many-perspectives view, which she contrasts with theone-perspective viewascribed to defenders of ME, children can switch conceptual perspectives more orless from the time they start building up a larger vocabulary in the second year oflife. Once children know that a rabbit is an animal, they can look at it as a rabbitand switch to considering it an animal. But they need not confront the fact that itcan be considered ananimalas well as arabbit.

Our claim (compatible with Clark’s) is that the ability to confront different per-spectives emerges around 4 years and underlies the co-emergence of success on theFB and the NN-tasks (and, of course, other perspective tasks: Level 2 visual per-spective taking and appearance–reality,Flavell, 1988; Perner, 1991). This locatesthe acquisition a few years earlier thanPiaget and Inhelder (1948/1956). However,if one strips their methods of unnecessary complexities (Light & Nix, 1983) thenthe age of acquisition comes closer to the age that we are dealing with here. Thecharacteristic feature of the NN-tasks is that one needs to keep both descriptions inmind in order to judge whether the other person (puppet) has used the alternativedescription. If alternative descriptions create different perspectives then childrenmust be able to confront different perspectives in order to make these judgements.The same ability is needed in the false belief task in order to represent that the objectis in location 2, but isbelieved to bein location 1. These two propositions can beintegrated in a single representation only by marking them as different perspectives.

9. Mutual exclusivity — a problem of dual identity or perspective?

It is now tempting to conclude that the ability to represent differences in per-spective frees children from the ME bias. This is not necessarily the case. For, from

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realising that I can conceive of a ‘thing’ under different sortals within differentperspectives it does not follow that the ‘thing’ can have both identities. If this didfollow, we would have to conclude from the fact thatan object in the cupboardcan be (mistakenly) conceived of asbeing in the drawer, that it must be possiblethat an object can be in the cupboard and in the drawer at the same time.

Clearly, we need to take into account the difference between truth-compatibleand truth-incompatible perspectives. The NN-task requires the ability to representtwo perspectives simultaneously, but does not require them to evaluate the truth ofboth claims. In a newrejection taskDoherty (2001)asked children between 3 and8 years to do exactly that. Children were first asked what something (e.g., a rabbit)is called. If they answered “rabbit” then a doll named Sally also called it a “rabbit”but Tony called it a “bunny.” Children then had to remember what Tony had said(bunny) and they were asked: “Is it a bunny?” The same procedure was repeatedfor what Sally had said it was. Children had few problems remembering what eachcharacter had said, but many children rejected one of the two labels (they didn’tthink it could be a bunny and a rabbit) which is indicative of the classical ME effect.

Not all children who failed the NN-task tended to reject (as one might havethought). This can be expected if some children were induced to switch perspec-tives with each switch to the other sortal. More interestingly, rejection didn’t stopaltogether with success on the NN-task around 4 or 5 years. Only around 7.5 yearsdid the rejection rate get close to zero. This considerable lag between success on theNN-task and subsidence of ME can be explained by fact that the NN-task requiresthe ability to confront a difference in perspective while ME can only be overcomeif the truth-compatibility of two perspectives can be assessed in addition.

The data, therefore, suggest that truth-compatibility is not understood beforethe age of 7–8 years. This gives us two interesting testable predictions. The firstprediction is that a similar lag should be observed for other truth-compatible per-spectives, e.g., visual perspective. Extrapolating from existing research (Kuczaj& Maratsos, 1975; Tanz, 1980) we assume that by 4 years of age children mightbe able to understand that whenA is in front of Bfor them, that another personviewing the scene from the opposite direction will say, “A is behind B.” However,when asked, “Is that right what other said?” children until 8 years will reject it.

Another interesting prediction can be derived from the consideration that under-standing truth-compatibility requires a kind of higher-order, perspective-relativetruth evaluation. The easiest way of deciding whether another person, who isclaiming something different, may be right or wrong is to simplyjudge the truthofother’s statementfrom within one’s own perspective. This works nicely for the falsebelief task. When Max on his return exclaims, “the chocolate is in the drawer,” acheck within my own perspective, where the chocolate is in the cupboard, leads tothe correct conclusion that his statement is false. The same strategy, however, doesnot work for visual perspectives. If we face each other over objects A and B, and Ievaluate your statement, “A is in front of B,” within my perspective then I come tothe wrong conclusion that your statement is false, because for me B is in front of A.And, it does not work for conceptual perspective changes arising from alternative

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naming, because when one is taking the perspective whereit is being individuatedas a statue thenit is nota piece of clay (with ‘is’ in the sense of individuation).

A higher-order strategy of evaluating truth within your perspective is neededhere. Data from a belief task used byPerner and Howes (1992)andPerner (1994)point to a later age of acquisition. Children had to predict what Max would answer tothe question, “Where is your chocolate?” As one would expect from previous data,practically all 4–6-year olds predicted correctly his mistake. However, childrenalso were asked to predict what Max would say to the question, “Do youknowwhere your chocolate is?” Now many of these children responded wrongly thathe would answer “No, I don’t know.” The main explanation for the difficulty ofthis question is that the answer requires the second-order understanding that Maxwill reflect (from within his perspective) approvingly on the truth of his belief,in other words,he thinks he knows. On the basis of these results we can venturethe following predictions. Children will misjudge the truth of truth-compatiblestatements as false until they are able to master the second-order strategy at about6 years. Until that age, many children are expected to misjudge another person’strue spatial statement phrased within an egocentric reference frame (e.g., “A is infront of B”) when spoken from a different vantage point as false, and will rejectthe application of one of two alternative sortals in Doherty’s rejection task.

This, however, cannot be the end of the developmental story. The child mustalso learn when the truth needs to be evaluated within her own perspective andwhen it needs to be evaluated within the other’s perspective. If every statementis evaluated within the other’s perspective then false beliefs will be misjudgedas true. Plausibly this distinction is acquired with the ability to evaluate truthrelative to other perspectives. However, the possibility exists that this acquisitionmay take additional years leading to a period of children’s regression in theirability to judge the falseness of false beliefs, and a stage of uncertainty aboutrejecting synonyms. Such uncertainty could be the reason for Doherty’s findingthat some children keep occasionally rejecting synonyms up to the age of 7 or even 8years. But these speculations are in need of systematic and, preferably, longitudinalinvestigation.

10. A new perspective including class inclusion

10.1. Back to Piaget

The ability required in the alternative naming tasks to acknowledge that some-thing can be arabbit and ananimalat the same time should be a critical prereq-uisite for passingInhelder and Piaget’s (1964)classic class inclusion test. For,asked about a group of three rabbits and two cats, whether there are more rab-bits or more animals, one has to count the rabbitsas rabbitsand as animals.Our analysis claims that two perspectives are involved. Independent counts (Howmany rabbits? How many animals?) can be provided by switching perspectives.

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Children (provided they can count) should be able to do this before they masteralternative naming and the false belief task. However, the class inclusion questionasks for comparison of both sets and so both perspectives need to be confronted.Moreover, children need to be aware that the numbers they attain within eachperspective are both accurate (true), which suggests that children solve the classinclusion problem at the same time as they can answer the know-question byPernerand Howes (1992)and when they stop rejecting on Doherty’s rejection task. Tosettle this issue we would need more information of how children approach theclass inclusion task. The variability found with different task procedures (Winer,1980) might be due to how these procedures influence children’s approach to thetask.

11. A Piagetian epilogue

In our attempt to explain why alternative naming and understanding false be-lief are developmentally related we made use of several Piagetian ideas. (1) Weused Piaget’s constructivist view of intellectual development for our definitionof perspective. (2) We used Piaget’s and Inhelder’s notion that an understand-ing of perspective is acquired in early-to-middle childhood as a powerful tool tointegrate different developments at the age of 4 years. (3) By differentiating be-tween truth-compatible and truth-incompatible perspectives we were able to give anew — and hopefully productive — perspective on mutual exclusivity and how itrelates to Inhelder and Piaget’s class inclusion task.

Acknowledgments

We would like to thank the staff and children of the Magistrat Kindergärtenin Auwiesenstrasse 22-24 and 60, Neutorstrasse, Maxglan, the PfarrkindergärtenHerrnau, Nonntal, Parsch and the Gemeindekindergärten Radstadt and Ramsaufor their participation in these studies. The project was financially supported bythe Austrian Science Fund (Project P14495-SPR) and by a research grant from theFaculty of Natural Sciences, University of Salzburg, to Manuel Sprung.

Appendix A

Items for the test phase of the say-something-different tasks.

Tasks Production version Judgement version

Synonyms Woman/lady [Frau/Dame] Train/railway [Zug/Eisenbahn]Aircraft/plane[Flugzeug/Flieger]

Matches/machsticks[Zünd-/Streichholz]Stool/chair [Sessel/Stuhl]

1470 J. Perner et al. / Cognitive Development 17 (2002) 1451–1472

Appendix A (Continued)

Tasks Production version Judgement version

Categories Pear/fruit [Birne/Obst] Pliers/tool [Zange/Werkzeug]Rabbit/animal [Hase/Tier] Apple/fruit [Apfel/Obst]

Cat/animal [Katze/Tier]

Colour/name Blue/cup [Blau/Tasse] Red/car [Rot/Auto]Green/snail [Grün/Schnecke] Blue/flower [Blau/Blume]

Red/ball [Rot/Ball]

Part/name Donkey/ears [Esel/Ohren] Elephant/snout[Elefant/Rüssel]

Snowman/nose[Schneemann/Nase]

Monkey/tail [Affe/Schwanz]

Dragon/head [Drache/Kopf]

Colour/colour Yellow/green tree[Gelb/Grün]

Yellow/blue bee [Gelb/Blau]

Yellow/blue fish [Gelb/Blau] Green/red present [Grün/Rot]Blue/red tricycle [Blau/Rot]

Part/part Head/tail [Kopf/Schwanz] Nose/mouth [Nase/Mund]Wing/head [Flügel/Kopf] Head/tail [Kopf/Schwanz]

Head/belly [Kopf/Bauch]

Note: The German originals are in the square brackets. The pairs used in thesynonyms task are used fairly synonymously in German, which is not the case fortheir English translations.

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