Running head: EPISODIC MEMORY DEVELOPMENT Episodic memory development: Theory of mind is part of re-experiencing experienc ed events

TH E A T R I U M, S O U T H E R N G A T E, C H I C H E S T E R, W E S T S U S S E X P019 8SQ

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Infant and Child DevelopmentInf. Child Dev. 15: 000–000 (2006)

Published online in Wiley InterScience

(www.interscience.wiley.com) DOI: 10.1002/icd.517

Episodic Memory Development:Theory of Mind is Part ofRe-experiencing Experienced Events

Josef Perner*, Daniela Kloo and Edith GornikDepartment of Psychology, University of Salzburg, Hellbrunnerstr. 34, Salzburg,Austria

Two experiments with 312- to 61

2-year-old children showed thattheory-of-mind development is associated with the growth ofepisodic memory. Episodic memory was assessed by manipulat-ing informational conditions such that they permit or prevent theformation of episodic memories in terms of re-experiencing therecalled event. Only experienced events, e.g. seeing how one putsa picture of a frog into a box, can be remembered by re-experience. Events known through indirect information cannotbe re-experienced, e.g. putting pictures into the box whenblindfolded and being later shown on video what was on thesecards. Children were also tested on a battery of theory-of-mindtasks assessing their understanding of the origins of knowledge.There was a significant interaction in both experiments showingthat recall of directly experienced items improved in relation toindirectly presented items the higher children’s theory-of-mindscores. The discussion suggests that episodic memory develop-ment is specifically linked to the growing ability to introspect anongoing experience and interpret it as representing an actual pastevent. Copyright # 2007 John Wiley & Sons, Ltd.

Key words: episodic; memory; theory of mind; remember know;introspection; direct experience

��

Since the notion of episodic memory is being used with different shades ofmeaning, we first sharpen the sense in which we intend to use it, along the linesintroduced by Tulving (1972, 1985) and elaborated by Wheeler, Stuss, and Tulving(1997). There are three important characteristics:

(1) Tulving (1985, p. 3) characterized episodic memory as remembering withreference to Ebbinghaus (1885, p. 1) as ‘calling back into consciousness aseemingly lost state that is then ‘immediately recognized as somethingformerly experienced.’’

3B2ICD : 517 PROD.TYPE: COM ED:DURGA

PAGN: J.SOLLY SCAN:pp.1^20 (col.¢g.: NIL)

*Correspondence to: Josef Perner, Department of Psychology, University of Salzburg,Hellbrunnerstr. 34, A-5020 Salzburg, Austria. E-mail: [email protected]

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(2) Episodic memory allows for reliving of the original experience or for re-experiencing of the remembered event: ‘Episodic memory . . . is the memorysystem that mediates mental time travel [in distinction to the possibility for] aperson to know about events in the past, . . . without mentally traveling backto re-experience the retrieved event’ (Wheeler et al., 1997, p. 332). This putsepisodic memory as remembering the past apart from knowledge of the past. Itgoes beyond mere knowledge that something has happened and also beyondknowledge that one has experienced the event. By re-invoking (parts of) theoriginal experience episodic memory gains a particular intimacy that pureknowledge cannot provide.

(3) Episodic remembering can be empirically distinguished from knowledge ofthe past, Tulving (1985) suggested, by judging retrieved items as‘remembering’ their presentation as opposed to just ‘knowing’ that theseitems had been presented. This method has subsequently become the maindirect test (e.g. Gardiner, 2001) for episodic memory.

From these three characteristics of episodic memory it follows that episodicmemory requires certain theory-of-mind (ToM) abilities that may be missing inyounger children. For instance, characteristic 1 requires that an event one nowremembers (e.g. the picture of the frog was put inside the box) be recognized assomething formerly experienced. For this recognition, children need to under-stand that their present memory of the event originates in their earlier witnessingof the event. Children before the age of 4 or 5 years seem not to have thisunderstanding (Gopnik & Graf, 1988; Taylor, Esbensen, & Bennett, 1994;Wimmer, Hogrefe, & Perner, 1988).

Similarly to be able to relive an earlier experience (characteristic 2), childrenneed to understand how the current, recollective experience (of re-experiencingthe earlier experience) relates to the earlier, original experience. In other words,children have to understand that their recollective experience represents theearlier experience. It has been claimed that children do not possess thisunderstanding before they can pass false-belief tests at about 4 years (Flavell,1988; Forguson & Gopnik, 1988; Perner, 1988; see also Povinelli, Landau, &Perilloux, 1996; Povinelli, Landry, Theall, Clark, & Castille, 1999).

From the characterization of episodic memory as the ability to remember anevent in distinction to just knowing that the event had happened (characteristic 3),Tulving (1985) developed an empirical test for the distinction in form of the muchused remember-know test. Unfortunately, it is difficult to find suitable instructionsfor explaining to adults the intended use of these terms. Consequently, it looksunpromising to try to ask 3- to 5-year-old children, for example, not only whetherthey put a certain picture into the box but also to indicate whether they rememberor merely know that they put the picture in the box.

In order to develop a suitable approach for children we take advantage of thefact that remembering an event requires direct perceptual contact with theremembered event. Evidently, only experienced events can be objectively re-experienced, and subjective impressions of a re-experience that lack such a basiscan only count as a ‘false memory’ (e.g. Loftus, 1979). Knowledge of an event, incontrast, can also come from indirect sources like testimony or inference. Forinstance, if a person has been to someone’s party and enjoyed herself theregreatly then the following assertion would be perfectly acceptable:

(1) I remember your party, all the lovely dancing, etc. In contrast, consider theperson not having been at the party but having received a detailed report

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Copyright # 2007 John Wiley & Sons, Ltd. Inf. Child Dev. 15: 000–000 (2006)DOI: 10.1002/icd

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from a reliable friend. This person, then, could not claim remembering theparty. Sentence (1) would sound like a lie. She can only claim to know variousdetails.

(2) I know that you had a birthday party and that there was a lot of nice dancing,etc.

Of course, we cannot exclude the possibility that a most lively description ofthe party paired with a particularly vivid imagination of the listener can lead tothe subjective impression in the listener that he or she ‘remembers’ the party.Work on source monitoring (Johnson, Hashtroudi, & Lindsay, 1993) shows thatone criterion for judging the source of recalled information is the vividness ofperceptual detail. If such detail is supplied by imagination, these internallygenerated features can be mistaken for originating in external input leading to aloss in reality monitoring (Johnson & Raye, 1981). In fact, verbal repetition ofeven fictitious events has a demonstrable effect on raising confidence that itoccurred (Garry, Manning, Loftus, & Sherman, 1996; Hyman & Pentland, 1996;Sharman, Garry, & Beuke, 2004). If added detail can lead to mistaking fiction forreality, it can also lead to mistaking indirectly gained information about an eventfor a trace of a direct experience. In this case, the listener’s later claim ‘toremember the party’ would not be a lie but a mistake (a ‘false memory’ of theparty).

Importantly, if such a false memory is formed then indirectly presentedinformation would not differ in its likelihood to be remembered from directlyexperienced events. However, if we assume that (true) episodic memoriesresulting from direct experience of an event are more likely than (false) episodicmemories resulting from indirect information about the event, then directlyexperienced events will be more likely to be recalled than events one was onlytold about. This should be particularly important under free recall. According toTulving (1985), free recall depends heavily on the existence of episodic traces, sothat one can retrieve events on the basis of what one has experienced, in contrastto cued recall, where one is also given helpful cues for particular items (e.g.classification cues: Which animals did you put in the box?), which help bring acorrect answer to mind even when no episodic trace is available.

Having mentioned source monitoring (Johnson et al., 1993) we should discussthe relationship between source memory and episodic memory. Although sourcememory is an important part of episodic memory it should not be equated withit. The ability to recall the source of information does not require episodicmemory, because it can be based on knowing and need not be remembered. Itmakes perfect sense for our hypothetical party absentee to say to the person whoinformed her about the events at the party: ‘Even though I can’t remember youtelling me, I still know that you and not someone else told me about the party.’Moreover, episodic memory does not need more than a very basic sourcedistinction between experienced and not-experienced events. It does not need therefined and clear distinction between different indirect sources, for example, whowas the informant about the party, which is usually assessed by source memorytests.

To assess episodic memory we need to contrast indirectly gained informationwith direct experience as illustrated in our common place party example.However, in this example the type of experience is confounded with thevividness of visual and other sensory sensations. When experiencing the partyone has rich visual, auditory, olfactory and other sensory inputs, while when

Episodic Memory Development 3

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merely being told about it one receives only comparatively arid linguisticinformation. Apart from its influence on source and reality monitoring, therichness of input seems to make pictures much more memorable than verbaldescriptions (e.g. picture superiority effect: Dewhurst & Conway, 1994; Rajaram,1996). Such a large difference may make it difficult to detect a developmentalinteraction with the two types of experience. In order to avoid this confound, wetried to implement the distinction between being a witness to an event andknowing of it through testimony with the following procedure.

In the direct-experience condition, children were asked to insert cards with simpleobjects drawn on them into a box. Later they were asked to recall which picturesthey had put into the box. In this condition children could answer this questionby remembering which card they had put into the box by trying to re-experiencetheir earlier experience of putting each particular picture into the box.

In the indirect-information condition, children could not see the pictures on thecards they put into the box. They were later shown a video with the pictures thatwere on those cards. So children could later recall which pictures they had placedinto the box, because they knew from the video what these pictures were. Butthey could not possibly (unless a false memory was formed) base their recall onremembering putting these cards into the box, since they could not genuinelyattempt to re-experience events they had not witnessed before. In fact, beingtested in the indirect-information condition oneself, one could only claim ‘toremember seeing a particular item on video’ (and therefore know that one had putthis item into the box), but one could not claim ‘to remember putting the item intothe box.’

Remembering an event, which requires episodic traces of the event, is thoughtto be particularly important for free recall (Tulving, 1985), and items recalled areindeed very likely (92%) to be judged ‘remembered’ in a subsequent recognitiontest of all items (Mangels, Picton, & Craik, 2001; see also Jones & Roediger, 1995,and a critical voice from Hamilton & Rajaram, 2003). Hence, we expect thefollowing for children’s free recall: (1) children with the prerequisite cognitiveabilities for forming episodic memories will do better in the direct-experiencecondition than in the indirect-information condition. This we expect becausedirect experience of events provides them with episodic traces, without whichfree recall is difficult, and which indirect information (barring formation of falsememories) does not provide. (2) Children without the cognitive prerequisites forepisodic memories cannot take advantage of directly experiencing individualitems being put into the box. Consequently, their free recall should be roughly thesame in the two conditions. This last prediction needs to be qualified if recall inthe direct-experience condition is already superior for other reasons. Then, itssuperiority should be less pronounced than for the more advanced children.

Perner and Ruffman (1995) and Naito (2003) reported evidence that children’sadvances in ToM, in particular their growing understanding of the sources ofknowledge and their ability to anticipate which sense modality to use for aparticular property (tunnel test) correlate significantly more strongly withimprovement in free recall than in cued recall. This is to be expected under theassumption that free recall depends more heavily on the availability of episodictraces than cued recall. Hence, this result was interpreted to show that acquisitionof these elements of a ToM is developmentally related to the emergence ofepisodic memory.

In the approach taken by Perner and Ruffman (1995) the presence of episodicmemory is inferred from contrasting retrieval modes; free versus cued recall,which are deemed to depend to different degrees on the availability of episodic

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traces. The research reported in this paper tries to approach the same issue fromthe encoding end, by manipulating the informational conditions such that theyallow (direct experience) or prevent (indirect information) the formation ofepisodic memories. This new approach is also an important theoretical advance.In contrast to comparing free with cued recall as a measure of episodicremembering, we take advantage of the necessary connection between thedirectness of experience and episodic memory: only directly experienced eventscan possibly}except for false memories}be re-experienced.

EXPERIMENT 1

Method

ParticipantsFifty-four native German-speaking children (31 girls and 23 boys) from a

nursery school in a town near the city of Salzburg participated in the study. Mostparticipants came from a middle-class background. Children’s ages ranged from3,7 (years,months) to 5,11 (M ¼ 4; 10; S:D: ¼ 7:68 months). To analyse and displayage trends, we divided the children into three approximately same size agegroups: 17 children from 3,7 to 4,4 (M ¼ 4; 1; S:D: ¼ 2:73 months), 19 childrenranging in age from 4,6 to 5,2 (M ¼ 4; 10; S:D: ¼ 2:60 months), and 18 childrenranging in age from 5,3 to 5,11 (M ¼ 5; 7; S:D: ¼ 2:41 months).

DesignEach child was tested individually in a quiet room of the nursery school.

Children were given two memory tasks (one with direct experience and one withindirect information). In addition, children received a ToM test battery assessingtheir ToM understanding. For this battery, one test assessed understanding of themodality specificity of perception (O’Neill, Astington, & Flavell, 1992), anotherthe understanding of the origins of knowledge (Wimmer et al., 1988), and twotested the understanding of false beliefs (traditional false-belief tasks: Wimmer &Perner, 1983). All tasks were administered in two sessions a few days apart. Eachsession started with presentation of items for the memory task and ended withrecall of memory items. In order to introduce some delay between encoding andretrieval, the ToM tasks were used between presentation of items and test. Tominimize carry-over effects across belief tasks, they were administered indifferent sessions. In the first session, children were given the source-of-knowledge test and one false-belief task between presentation and recall ofmemory items. In the second session, presentation and recall were separated bythe modality-specificity test and the other false-belief task. Half of the childrenreceived the direct-experience memory task in the first session and the indirect-information memory task in the second session; the other half started with theindirect-information memory task.

Procedure and materialsMemory tasks. For the memory tasks, four sets of 12-coloured pictures

(21� 29.7 cm) of familiar objects, animals, or human beings were used. Sets 1and 2 were administered in the first session. Sets 3 and 4 were given in the secondsession. In each session, half of the children were given a particular set as testitems and the other set as distractor items. For the other half, the two sets were


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exchanged, so that each set was equally often used as test or distractor set in thedirect-experience and indirect-information memory task.

As a means of sharpening the detection of episodic traces from amongfamiliarity based recall we presented children beforehand with the pictures to beput into the box mixed up with the distractor set. Children’s episodic memory ofthe items put into the box can then be assessed by the difference of the number ofcorrect items recalled and the number of distractor items mentioned.

The experimenter presented the 24 pictures, one after the other, alternatingbetween items from the test and distractor set. As each picture was produced, thechild was asked to name it. If necessary (which was rarely the case), theexperimenter provided the correct label. This was done in order to know whatthe child’s natural label for the object is and to avoid uncertainty of whether thechild is recalling a correct or an incorrect item in the test phase.

In the direct-experience memory task, children were then asked to place the 12 testitems into a (26� 40� 4 cm) box. They were allowed to look at each picture for 2 sand were instructed to keep these pictures in mind. After 2 s, the experimenterknocked on the table. This was the sign for the children to put the item face downin the box. If a child looked at a picture for less than 2 s (which was rarely thecase), she was reminded to look carefully at the pictures until the experimenterknocked on the table. In the indirect-information memory task, children were alsoasked to place the 12 test items into a box but they were blindfolded so that theycould not see the pictures. After having placed the 12 items into the box, theywere shown ‘what these 12 pictures had depicted’ by means of a videopresentation. Each picture was shown for 2 s, and children were instructed tokeep these pictures in mind. After the intervening tasks, children were asked inboth memory tasks, ‘Do you remember the pictures you put into the box?’ Ifchildren answered with an item that was not put inside the box it was scored as afalse alarm.

On both memory tasks, the number of correct recalls and the number of falsealarms (if children mentioned items that were not put inside the box) wererecorded. Mostly, false alarms comprised items from the distractor set used in thefamiliarization phase. The distractor set was introduced to get a more precisemeasure of remembering the pictures being put into the box as opposed to merefamiliarity with the pictures. The contrast between recall of items placed insidethe box with false alarms (mostly items that children were familiarized with butdid not put inside) sharpens the detection of episodic memories in contrast tomere familiarity answers. For instance, a child who recalls two correct items andno distractors is comparable with one who recalls 12 targets and 10 distractors.Both children vastly differ in recall of familiar items (pictures) but are similarin terms of memory for items placed inside the box. This is critical, becauseour manipulation of direct experience and indirect knowledge pertains to theplacing of cards into the box, not to familiarity with the pictures (they aredirectly experienced in both conditions). For this reason, it is essential to rely notonly on the quantity of pictures recalled (number of placed pictures recalled inrelation to all pictures placed into the box) but also check for accuracy (number ofplaced pictures recalled in relation to all pictures recalled; as this terminology isused by Koriat & Goldsmith, 1996, p. 177). A measure that captures both theseaspects common in signal detection theory is d0 which is based on the differencebetween hits and false alarms. This is typical for forced-choice recognitiontasks and rarely used with recall (Koriat & Goldsmith, 1996, p. 183). Followingthis approach, we use the difference between number of correct items recalledminus number of false alarms as our critical indicator of episodic recall and refer

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to it, for want of a shorter label and in line with signal detection theory, as: recallaccuracy.

Source-of-knowledge test (Wimmer et al., 1988). This task consisted of threesubtasks: in one subtask, children simply observed the object being put inside abox. In the other two subtasks, children were told to close their eyes while theobject was put inside a box. In one of these two tasks, however, the child was toldwhich object was placed inside the box while in the other no information wasgiven. Three different boxes were used: a purple one (29� 16� 10 cm), an orangeone (21�16.5� 8 cm), and a green one (18� 13.5� 8 cm). Three different objectswere placed inside these boxes: a ball was put inside the purple box, sunglasseswere put inside the orange box, and a bear puppet was put inside the green box.The order of materials (purple box–orange box–green box) was fixed, but theorder of subtasks was counterbalanced according to a Latin square design so thateach task was equally often paired with each material.

Children either (a) observed which object was put inside a box, or (b) they weretold what the object was, or (c) they were given no information at all. On eachsubtask, children were then asked, ‘Do you know what is inside the box?’ Mostlycorrect answers to this question were anticipated. The real measure of interestwas the ensuing justification question asking for the reason for the children’sknowledge or ignorance: ‘How do you know that?’ or ‘Why don’t you knowthat?’ One point was given for each correct answer, resulting in a total score from0 to 3.

Modality-specificity test (O’Neill et al., 1992). Following the standardprocedure, children were asked to predict which sense modality to use in orderto find out about a certain aspect (colour or weight) of an object. Childrenwere shown a plastic box with two openings (one at the top for looking inside itand one at the left for grasping inside it). In two familiarization trials, a toy carand a plastic spider were used. Children were first shown that they could findout what was hidden inside the box either by lifting the top opening and seewhat’s inside or by putting their left hand through the left opening and feelwhat’s inside.

For the four test trials, four pairs of objects were used: in the two feel trials, thepairs of objects looked the same but felt different in weight. (a) Two identicaltennis balls, one stuffed with sand and one empty, and (b) two identical plasticbottles, one full of water and one empty, were used. In the two see trials, the pairsof objects felt the same but looked different: (a) two balls of the same size andshape, one orange and one black, and (b) two small cars of the same size andshape, one pink and one black, were used. The order of the four test trials wascounterbalanced according to a Latin square design with the constraint that see-and feel-trials alternated.

On each test trial, children were shown and told whether the objects looked thesame but felt different, or whether the objects felt the same but looked different.After children had finished examining the two objects, they were asked to turnaround. While they could not see the box, the experimenter put one of the objectsinside the box and stored the other one away. Then, children were given the testquestion, ‘To find out for sure whether (e.g.) the black or the pink car is inside,what do you have to do?’ If they did not respond they were given a forced choice:‘Do you have to lift the top and look inside, or do you have to use your hand andfeel the object?’ Children received a final score of 0–2. Two points were given forfour correct answers, 1 point was given for three correct answers. Zero pointswere given for up to two correct answers (out of four). The rationale for thisscoring was that zero to two correct answers give no indication of children


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understanding the task, because a child can get up to two answers correct bysimply opting for one particular modality.

False-belief tasks (Wimmer & Perner, 1983). Two unexpected transfer false-belieftasks were administered. The first story involved a boy looking for his book thatwas unexpectedly transferred and was enacted in a three-dimensional model(43� 26� 43 cm). The second was a picture story about a girl looking for herchocolate bar that was unexpectedly transferred. In each story, children had topredict the protagonist’s (e.g. Max’s) action based on the protagonist’s falsebelief: ‘Where will Max go first?’ One point was given for a correct answer toeach test question, resulting in a score from 0 to 2.

Finally, children’s scores on each ToM measure were transformed into valuesbetween 0 and 1. Then, a combined ToM competence score was computed byaveraging the transformed scores on the individual tasks. Children were thenclassified into three competence groups: a mean score of 0–0.50 was classified as‘low competence’, a mean score of 0.51–0.75 was classified as ‘mediumcompetence’, and a mean score of 0.76–1.00 was classified as ‘high competence.’

Results

Age differences and interrelations between tasksAge differences in task performance were analysed by a set of one-way

ANOVAs with age group as the factor of interest. This revealed significanteffects of age group for recall accuracy on the direct-experience memory task,Fð2; 51Þ ¼ 7:14; p50.01, partial Z2 ¼ 0:22; for the source-of-knowledge testscore, Fð2; 51Þ ¼ 5:87; p50.01, partial Z2 ¼ 0:19; for the modality-specificity testscore, Fð2; 51Þ ¼ 7:50; p50.01, partial Z2 ¼ 0:23; and for the false-belief test score,Fð2; 51Þ ¼ 4:93; p50.05, partial Z2 ¼ 0:16; but not for recall accuracy on theindirect-information memory task, Fð2; 51Þ ¼ 1:32; p>0.05, partial Z2 ¼ 0:05: Allthree ToM measures were correlated with correlation coefficients ranging from0.30 to 0.65 (all significant at p50.05). In order to increase the power of theanalyses using these measures we combined them into a single ToM-competencescore. In contrast, the two memory measures were not significantly correlatedwith each other (r ¼ 0:20; p>0.05).

ToM-competence and memory performanceChildren’s performance on the two memory tasks is shown in Table 1. The

developmental relation between ToM-competence and performance on thememory tasks was analysed by a repeated measures ANCOVA on recallaccuracy with experience (direct, indirect) as a within-participants factor, ToM-competence (low, medium, high) and memory task order (direct–indirect,indirect–direct) as between-participants factors, and age as a covariate. Therewas a significant main effect of experience, Fð1; 47Þ ¼ 4:09; p ¼ 0:049; partial Z2 ¼0:08: Children performed somewhat better on the indirect-information memorytask (M ¼ 2:61) than on the direct-experience memory task (M ¼ 2:24). There wasalso a significant experience � ToM-competence interaction, Fð2; 47Þ ¼ 5:60;p50.01, partial Z2 ¼ 0:19: This interaction is shown in Figure 1 and was due to thefact that children with high ToM-competence recalled directly experienced itemsbetter than indirectly experienced items. In contrast, children with low ToM-competence recalled indirectly experienced items better than directly experi-enced ones.

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Discussion of Experiment 1

This study demonstrates that growing ToM understanding goes along withenhanced episodic memory as measured by the recall difference across differentinformation conditions (direct experience versus indirect information). Theseresults confirm previous studies (Naito, 2003; Perner & Ruffman, 1995) showingthat ToM development is linked to the growth of episodic memory.

The present method differs from those previously used in the assessment ofepisodic traces. Previous studies measured episodic memory with free recall inrelation to cued recall of pictures. We measured it with free recall of directlyexperienced events involving pictures in relation to free recall when only indirectinformation about the event was available. This measure differs in an importantway from the previously used difference between free and cued recall inthat there is a necessary link between direct experience and episodic memory asre-experience of a recalled event.

Experiment 1 showed that, as expected, children with high ToM-competenceperformed better on the direct-experience memory task, whereas (unexpectedly)children with low ToM-competence performed better on the indirect-information

Table 1. Hits, false alarms, and recall accuracy on the direct-experience and indirect-information memory tasks in Experiments 1 and 2

Memory measure

Hits False alarms Hits-false alarms

Memory task Range Mean S.D. Range Mean S.D. Range Mean S.D.

Experiment 1 (N ¼ 54)Direct 0–7 3.09 2.01 0–3 0.85 0.94 �2 to 7 2.24 2.07Indirect 0–8 3.31 1.65 0–3 0.70 0.90 �1 to 7 2.61 1.78

Experiment 2 (N ¼ 38)Direct 0–7 2.68 1.77 0–11 1.60 2.33 �9 to 6 1.08 3.13Indirect 0–9 3.21 2.05 0–8 1.24 1.71 �8 to 8 1.97 2.82

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Figure 1. Recall accuracy of children in the three ToM-competence groups on the twomemory tasks in Experiment 1.


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memory task. Our explanation for this pattern of performance is as follows: theyounger children do not attempt to re-experience (relive) any earlier experience,since it does not make sense to them. Even though earlier experiences may bereplayed in their mind, they can not understand them as re-experiences of earlierevents and, consequently, cannot use them as a method for recalling these earlierexperienced events. The younger children only retrieve automatic associationsthat come to mind, and these should be about the same for directly experienceditems and indirectly gained information. However, they are slightly better withindirect information, presumably, because they can fully concentrate on lookingat the video without having to think about picking up the next picture and put itinside the box as in the direct condition.

The older children, when asked to remember which cards they had put insidethe box, try to re-experience (call up in their imagination) the event of insertingthe cards. In the direct condition this works. But in the indirect condition,re-experiencing how one put the cards into the box does not help at all. Theunsuccessful attempt to retrieve items this way may actually interfere with theautomatic retrieval used by the younger children; hence they produce feweritems than the younger children. This would explain the slight but counter-intuitive decline in memory for indirectly known items in Figure 1.

What the older children could do, is to make a strategic switch tore-experiencing what they had seen on video, knowing that everything theysaw on video are pictures they had put into the box. In fact, pilot results on adultssuggest that adults do exactly this and, therefore, they are as good in the indirectas in the direct condition, but do judge directly experienced items more often as‘remembered’ than indirectly known items (Stottinger, Kloo, & Perner, 2004). Asthe present data indicate, children at the age tested do not yet show this strategicsophistication of adults by making this strategic switch.

EXPERIMENT 2

The objective of this experiment is to examine whether the results of Experiment1 can be replicated by another experimenter. Furthermore, in both memory tasks,each picture was shown for 3 s instead of 2 s in order to enhance the recall rate.The false-belief tasks, due to near ceiling performance (84% correct), werereplaced by the when-did-you-learn test (Taylor et al., 1994), also used by Naito(2003) in connection with episodic memory.

Method

ParticipantsA total of 40 native German-speaking children were recruited from a nursery

school in a town near the city of Salzburg but from a different school than thechildren of Experiment 1. Two children were excluded from the final samplebecause their false alarm scores on the memory tests were three standarddeviations above the mean. The final sample comprised 38 children (18 girls and20 boys). Most participants came from a middle-class background. Children’sages ranged from 3,9 to 6,9 (M ¼ 5; 7; S:D: ¼ 10:67 months). To analyse anddisplay age trends, we divided the children into three approximately same sizeage groups: 13 children ranging in age from 3,9 to 5,5 (M ¼ 4; 6; S:D: ¼ 6:29months), 13 children ranging in age from 5,6 to 6,0 (M ¼ 5; 10; S:D: ¼ 1:98

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months), and 12 children ranging in age from 6,1 to 6,9 (M ¼ 6; 6; S:D: ¼ 2:71months).

DesignChildren were tested in a quiet room of the nursery school. The same tasks as

in Experiment 1 were used except that the false-belief tests were replaced by thewhen-did-you-learn test (Taylor et al., 1994). Administration of all tasks wasspread out over two sessions a few days apart. Each session started withpresentation of items for the memory task and ended with recall of memoryitems. In the first session, children were given the when-did-you-learn test andthe source-of-knowledge test between presentation and recall of memory items.In the second session, presentation and recall were separated by the modality-specificity test. Half of the children received the direct-experience memory task inthe first session and the indirect-information memory task in the second session;the other half started with the indirect-information memory task.

Procedure and materialsMemory tasks. The procedure of the memory tasks was the same as in

Experiment 1 with the following exceptions. In both memory tasks, each picturewas shown for 3 s instead of 2 s, with the aim to raise the average number ofevents recalled. The test items were placed into a yellow letter-tray and not into abox, to avoid unnecessary problems of inserting the card into a box by theyounger children. Problems with putting the cards into the box could havedistracted children from looking at the picture on cards carefully, which couldaccount for the fact that some children (the ones who did less well on the ToMmeasures) had better recall of indirect than directly presented events. For theindirect-information memory task, a PowerPoint presentation was used insteadof a video presentation.

When-did-you-learn test (Taylor et al., 1994). Following the standard procedurefor this test, children were taken to a separate table and shown a foldercontaining eight pictures. Four pictures consisted of familiar items (a pair oftrousers, a crocodile, a boat, and a frog), and the other four pictures consisted ofunfamiliar items (an armadillo, a gramophone, a chameleon, and a compass).Pictures were presented in the following fixed random order: pair of trousers,armadillo, gramophone, crocodile, chameleon, boat, frog, and compass. Prior totesting, a pilot test with seven children had been conducted to establish thefamiliarity/unfamiliarity of these items.

In the learning phase, children were instructed to name the pictures. They weretold, ‘Some of the pictures may be unfamiliar to you. If this is the case, simply tellme that you don’t know the name. I will then help you.’ The learning phasecontinued until children could name all four unfamiliar items.

After an intervening task (the source-of-knowledge test), the eight pictureswere presented again. Children were first instructed to name each picture. Then,the experimenter asked a forced-choice question, ‘Have you always known this,or did you learn this over there?’ This question is to assess when childrendevelop a notion that knowledge needs to be acquired. The standard finding isthat younger children answer with ‘always known’ and only older onesdifferentiate between items they have known before the experiment and thosethey have just learned about. The order of the answer alternatives wascounterbalanced. Performance was classified on a scale from 0 to 4. Zero pointswere given for up to four correct answers (out of eight) because these scores can


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only be due to guessing or other response strategies unrelated to the subjectmatter, 1 point was given for each additional correct answer up to a maximum of4 points for eight correct answers.

For the source-of-knowledge test and the modality-specificity test, materials andprocedure were the same as in Experiment 1. Children’s scores on each ToMmeasure were transformed into values between 0 and 1. Then, a ToM-competencescore was computed by averaging these transformed scores. Children were thenclassified into three ToM-competence groups as in Experiment 1.

Results

Age differences and interrelations between tasksFirst, age differences in task performance are reported. As in Experiment 1, a

set of one-way ANOVAs with age group as the factor of interest revealedsignificant effects of age group for recall accuracy on the direct-experiencememory task, Fð2; 35Þ ¼ 4:17; p50.05, partial Z2 ¼ 0:19; and for all three ToMtasks (when-did-you-learn test score, F½2; 35� ¼ 13:25; p50.001, partial Z2 ¼ 0:43;source-of-knowledge test score, F½2; 35� ¼ 12:02; p50.001, partial Z2 ¼ 0:41;modality-specificity test score, F½2; 35� ¼ 17:69; p50.001, partial Z2 ¼ 0:50); butnot for recall accuracy on the indirect-information memory task, Fð2; 35Þ ¼ 2:28;p > 0:05; partial Z2 ¼ 0:11: All three ToM measures were correlated withcorrelation coefficients ranging from 0.44 to 0.58 (all significant at p50.01)providing a justification for the ToM-competence score. However, as inExperiment 1, the two memory measures were not significantly correlated witheach other (r ¼ 0:22; p > 0:05).

ToM-competence and memory performanceChildren’s performance on the two memory tasks is shown in Table 1. The

developmental relation between ToM-competence and performance on thememory tasks was analysed by a repeated measures ANCOVA on recallaccuracy with experience (direct, indirect) as a within-participants factor, ToM-competence (low, medium, high) and memory task order (direct–indirect,indirect–direct) as between-participants factors, and age as a covariate. The onlysignificant effect was the experience�ToM-competence interaction, Fð2; 31Þ ¼5:79; p50.01, partial Z2 ¼ 0:27: As in Experiment 1, this interaction shown inFigure 2 was due to the fact that children with high ToM-competence recalleddirectly experienced items better than indirectly conveyed items. In contrast,children with low ToM-competence recalled indirectly conveyed items betterthan directly experienced ones.

Discussion of Experiment 2

Comparing recall performance in this experiment with that in Experiment 1shows that the longer inspection time of items (3 instead of 2 s) did not lead to thehoped for increase in number of items recalled (see Table 1). In this experiment,we also avoided the need to insert cards into the boxes, which may have beendistracting children from looking carefully at the picture on the card and mayhave led to the worse recall of directly experienced items than of indirectlypresented items. However, as the data show, this difference was still presentamong the children with less developed ToM understanding, just as in

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Experiment 1. Most importantly, the present results confirmed the theoreticallyimportant results of Experiment 1. Only recall accuracy of directly experiencedevents increased with ToM competence, but not recall of indirectly presenteditems. This pattern of results we interpret as evidence that episodic rememberingdepends on ToM development, since only directly experienced events can beepisodically re-experienced but not indirectly presented items.

GENERAL DISCUSSION

The results from both experiments confirm the relationship between ToMdevelopment and the growth of episodic memory previously reported by Pernerand Ruffman (1995) and by Naito (2003). These earlier studies relied on thedifference between free and cued recall as a measure of episodic remembering.We used a measure more directly related to episodic memory as re-experiencingearlier episodes by contrasting free recall of originally experienced events withrecall of events known through indirect information. In particular, as childrenacquire an understanding of the sources of knowledge and can anticipate fromwhich sense modality they will get information about a particular propertyepisodic memory becomes possible or, cautiously interpreted, improves.

Perner and Ruffman (1995) as well as Naito (2003) identified the presence ofepisodic memory with the difference between retrieval modes (free versus cuedrecall). We identified it with the recall difference across different informationconditions (direct experience versus indirect information). The two studiestogether show that, however, the specific episodic memory ability is captured,one finds a link between it and ToM development.

In our introduction we identified different distinctive features of episodicmemory, in particular: (a) recognition of the retrieved information as somethingpreviously experienced requires an understanding of sources of information, and(b) the recollective experience needs to be understood as a representation of anearlier experienced event. Presumably, since these two-component abilities areboth necessary for episodic memory, the one which develops last will dominate

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Figure 2. Recall accuracy of children in the three ToM-competence groups on the twomemory tasks in Experiment 2.


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the onset of episodic memory. Experiment 1 showed that the representationalunderstanding, as measured by the false-belief test, develops too early to havethe decisive impact. In fact, an ANOVA using only false belief instead of thecompound ToM-competence measure shows no significant interaction withinformation condition, Fð2; 49Þ ¼ 0:88; p > 0:40; partial Z2 ¼ 0:03: This suggeststhat children understand that their recollective experience represents an eventbefore they can encode that their recollective experience was caused byexperiencing the represented event.

Experiment 2 showed that the modality-specificity test dominated the when-did-you-learn test in its predictive value of memory performance: an ANCOVAwith the modality-specificity test as a covariate leaves no variance to beexplained by the when-did-you-learn test, Fð4; 27Þ ¼ 0:48; p > 0:70; partial Z2 ¼0:07; while an ANCOVA with the when-did-you-learn test as a covariate leavessignificant variance to be explained by the modality-specificity test, Fð2; 31Þ ¼4:07; p50:05; partial Z2 ¼ 0:21:

Finally, an ANCOVA for Experiments 1 and 2 combined with the source-of-knowledge test as a covariate leaves significant variance to be explained by themodality-specificity test, Fð2; 85Þ ¼ 3:56; p50:05; partial Z2 ¼ 0:08:

This result raises the interesting question of what part of episodic memoryprocesses the modality-specificity test captures that the source-of-knowledge testdoes not touch upon. To answer this question, we can offer only speculation thatputs a somewhat different interpretation on the data than the one just outlinedabove.

Our speculation centres on the development of introspection as a thirdnecessary component in addition to the two already identified. When children leta past event run through their mind again (recollective experience), we havepointed out, they need to understand that (a) what they experience has its originin an actual event (understanding source of their experience/knowledge) and (b)that this experience is a representation of the original experience (i.e. a re-experience). To this we can add the third aspect, namely that (c) a recollectiveexperience requires introspective abilities. Unlike a video record of a past event,an episodic memory consists only of a purely mental, internal image (one shouldnot think of this as just visual imagery but also olfactory, auditory, and othersensory modalities, and even motor imagery, e.g. Jeannerod, 1997). This purelyinternal image of the past event needs to be introspectively contemplated.

One could argue that the modality-specificity test requires a combination ofthese three elements on the assumption that children, when they are asked howto find out about an object’s colour (or weight) inside a tunnel in the modality-specificity test, they imagine themselves looking at or grasping the object andintrospect whether each action provides a possible answer about colour. Hence,performance on this task predicts episodic memory the best because it combinesintrospection of an internal imaginative experience with interpreting thisexperience as informative about the actual action to be carried out, in a similarway in which episodic memory requires introspection of an internal recollectiveexperience interpreted as representing an actual past event.

The other ToM tasks used do not require a combination of all three elements.For understanding that a story character, who failed to witness an unexpectedtransfer of an object, mistakenly thinks that the object is still in its originallocation one does not have to imagine the story character’s experiences (thoughsome simulation theorists would assume so, e.g. Goldman, 1993). Similarly, whenseeing an object being put into a box in the source-of-knowledge test, then onesimply realizes that one knows which object is inside from having seen it. If one

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had forgotten, that one has seen the object being put inside, it seems impossibleto recover this information from introspecting on some internal imaginativeexperience.

Our speculation about introspective features being critical also fits Naito’s(2003) finding that the ‘deceptive appearance’ false-belief task was a betterpredictor of episodic memory than the ‘unexpected transfer’ false-belief test. AsNaito herself argued, in the deceptive appearance task children first experiencethemselves having a belief (that a chocolate box contains chocolates) which turnsout to be false (the box contains a tooth brush). Plausibly, this earlier ownexperience is invoked when children are either asked what they themselvesthought was in the box or to predict how someone else would answer in thissituation. To the degree that children do use this strategy, they have to introspecta recollection of an experience and interpret it as a representation of their ownpast experience or of the actual future experience of another person. Since thisown experience is missing in the unexpected transfer version children are lesslikely to use this strategy, which explains why the deceptive appearance versionof the false-belief task was a better predictor of episodic memory than theunexpected transfer version, in line with our speculation.

Research in the last 10 years found that ToM development over the 3–6 yearsperiod coincides with several other memory developments, which are closelyrelated to episodic memory but also need to be distinguished from it.

Recollection versus Familiarity

Episodic memory has been described as involving a recollective experience (e.g.Wheeler et al., 1997) which is missing in pure knowledge about the past. This hasled theorists (e.g. Brainerd, Holliday, & Reyna, 2004; Yonelinas, 2001) to identifythe difference between remembering and knowing with the distinction betweenrecollection and familiarity. This distinction was introduced by Mandler (1980:elaborative and integrative) and captures the phenomenological differencebetween definitely recognizing an item as old versus merely having a feelingof familiarity of having encountered this item before. Although we think thatepisodic memory tends to be associated with recollection in this sense, it shouldnot be equated with it for the following reasons. The distinction betweenrecollection and familiarity has also been used by Jacoby (1991) to mark thedistinction between explicit and implicit memory, hence, the distinction betweenremembering and knowing is different as these are thought to be two kinds ofexplicit memory (e.g. Baddeley, 2001). Moreover, recollection in Mandler’s sensecan also be based on knowing, and need not imply remembering. That is, one canclearly know that one has encountered an item before (beyond any vague feelingof familiarity) and, yet, not be able to relive this experience. This observation alsoimplies that knowing should not be equated with familiarity as Conway,Gardiner, Perfect, Anderson, and Cohen (1997) requested their experimentalparticipants to explicitly distinguish between ‘remember’, ‘know’, ‘familiarity’,and ‘guess’ responses. Nevertheless Brainerd et al. (2004) found that childrenbetween 5 and 14 years show marked increases in recollective experiences butonly slight increases in familiarity experiences. This finding is relevant from ourpoint of view, since the distinction between recollection and familiarity,presumably, requires similar introspective abilities as episodic memory. How-ever, it remains difficult to account for our finding with the recollection–familiarity distinction, since our two information conditions do not differ in the


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relevant aspects. Exposure to the visual details of each item was the same in theindirect-information condition (shown on video or computer) as in the direct-experience condition (visible on cards). Therefore, it is difficult to see how anincrease in recollective experiences should affect recall in the direct conditionmore than in the indirect condition.

Source Memory, Reality Monitoring, and Suggestibility

As our first characteristic of episodic memory we listed recognition of the contentof the recollective experience as something formerly experienced (Ebbinghaus,1885). This implies the ability to distinguish and remember sources ofinformation. There have been several reports that source memory and realitymonitoring improve in the age bracket from 3 to 5 or 6 years (Drummey &Newcombe, 2002; Roberts & Blades, 2000; Robinson, 2000; Sluzenski, Newcombe,& Ottinges, 2004; Whitcombe & Robinson, 2000) in line with ToM development(Naito, 2003). Improvements in source memory have also been specifically linkedto significant reductions in suggestibility in this age range (Ceci & Bruck, 1993;Giles, Gopnik, & Heyman, 2002; Leichtman, Morse, Dixon, & Spiegel, 2000), andsource memory training can reduce suggestibility (Thierry & Spence, 2002). Thisis to be expected since memory of source enables a more critical appreciation ofthe relative trustworthiness of received information. Moreover, since ToMdevelopment is linked to source memory, which is linked to reductions insuggestibility, progress in ToM is also related to reductions in suggestibility(Welch-Ross, 1999; Welch-Ross, Diecidue, & Miller, 1997; though Templeton &Wilcox, 2000, came to the opposite conclusion).

Although improvements of source memory may lead to improved recall, it isdifficult to understand our results purely in these terms, because it would notexplain why recall improves particularly for directly observed events but onlymarginally (or not at all) for information from indirect sources as children getmore sophisticated in understanding their mind. It is this differential relationshipbetween recall of directly experienced events and ToM tests (the modality-specificity test in particular) that speaks for a specific relationship betweendevelopment of ToM and episodic memory, rather than other kinds of memorydevelopment, like better source memory.

CONCLUSIONS

The reported data reinforce the idea that theory of mind and episodic memorydevelopment are intertwined. This should not be understood as a claim thattheory of mind development is in any way prior to episodic memory. Rather, thedaily routines of reminiscing on the day’s events (Nelson, 1989) and theadvantage of having an elaborative mother (Fivush, 1991; Hudson, 1990; Welch-Ross, 2001) may be prime movers of memory as well as theory of minddevelopment through the fostering of episodic memories.

The finding that the modality-specificity test proved to be the best predictor offree recall of directly experienced events suggests that the peculiar combinationof introspecting recollective experiences and interpreting these experiences asbeing products and representations of actually experienced events may be theessential difficulty for young children. This, however, is only a suggestion that

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needs to be followed up in future research with clearer measures of children’sability to interpret mental images as representations of external events.

In sum, the present results confirm the relationship between theory of mindand episodic memory development shown in previous studies (Naito, 2003;Perner & Ruffman, 1995) with converging evidence from a novel andtheoretically more forceful indicator of episodic memory traces. Whereas,previous research used free recall over cued recall, we used free recall accuracy(hits minus false alarms) of directly experienced events over free recall accuracyof indirectly known events as the indicator of episodic memory. Using thiscontrast is theoretically sharper because there is a necessary connection betweenhaving experienced an event and the ability to later re-experience it (episodicmemory).

The results also confirmed that not all theory-of-mind measures are equallygood predictors of episodic memory. Understanding which sense modality to usefor getting information about a particular property (modality-specificity test)came out as a top predictor in several studies. It was a better predictor than thesource-of-knowledge test (also Perner & Ruffman, 1995) and the false-belief task(see also Naito, 2003) study. We speculate that the modality-specificity test shareswith episodic remembering the need to introspect an ongoing experience. In themodality specificity test one has to imagine looking inside or feeling the objectinside and then introspect what information one would get, and one has tounderstand that this provides information of what one will actually perceivewhen one carries out these actions. In episodic remembering one has to introspecton one’s recollective experience of re-experiencing an event and has tounderstand that this provides information about an actual event in the past: aspeculation in need of being tested.

ACKNOWLEDGEMENTS

This study is part of a research project financed by the Austrian Science Fund(FWF project P16215-G04).

The data of a pilot experiment were presented as a paper ‘Development ofEpisodic Memory and Theory of Mind: The Role of Direct Experience’ at theinvited symposium Autonoetic consciousness (Endel Tulving), XXVII InternationalCongress of Psychology, 23–28 July 2000, Stockholm, Sweden. The data of thispilot experiment and of Experiment 1 were presented as a paper ‘The Role ofDirect Experience in the Development of Episodic Memory’ at the symposiumLinking Reasoning about Mental States and Developing Memory for PersonallyExperienced Events, biennial meeting of the Society for Research in ChildDevelopment, 19–22 April 2001, Minneapolis, Minnesota.

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Running head: EPISODIC MEMORY DEVELOPMENT Episodic memory development: Theory of mind is part of re-experiencing experienc ed events