Consciousness and Cognition 19 (2010) 802–815

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Consciousness and Cognition

journal homepage: www.elsevier .com/locate /concog

Retro- and prospection for mental time travel: Emergence of episodicremembering and mental rotation in 5- to 8-year old children q

Josef Perner *, Daniela Kloo, Michael RohwerDepartment of Psychology, University of Salzburg, Austria

a r t i c l e i n f o

Article history:Available online 22 July 2010

Keywords:Episodic memoryMental rotationDevelopmentProspectionTheory of mindPreschool periodMental time travel

1053-8100 � 2010 Elsevier Inc.doi:10.1016/j.concog.2010.06.022

q This article is part of a special issue of this jour* Corresponding author.

E-mail address: josef.perner@sbg.ac.at (J. Perner)1 In response to an anonymous reviewer we need

Sometimes it is a concern about a specific future evenNielsen, 2009) but sometimes a timeless assumptionwill take my coat and not the swimsuit; Atance & Mimagined possibilities (i.e., although one intends to dooneself into) a past event that has actually taken plaimagined events in contrast to retrospection for re-e

Open access under CC

a b s t r a c t

We investigate the common development of children’s ability to ‘‘look back in time” (ret-rospection, episodic remembering) and to ‘‘look into the future” (prospection). Experiment1 with 59 children 5 to 8.5 years old showed mental rotation, as a measure of prospection,explaining specific variance of free recall, as a measure of episodic remembering (retro-spection) when controlled for cued recall. Experiment 2 with 31 children from 5 to 6.5years measured episodic remembering with recall of visually experienced events (seeingwhich picture was placed inside a box) when controlling for recall of indirectly conveyedevents (being informed about the pictures placed inside the box by showing the pictureson a monitor). Quite unexpectedly rotators were markedly worse on indirect items thannon-rotators. We speculate that with the ability to rotate children switch from knowledgeretrieval to episodic remembering, which maintains success for experienced events but hasdetrimental effects for indirect information.

� 2010 Elsevier Inc. Open access under CC BY-NC-ND license.

1. Introduction

We naturally speak of ‘‘looking back on past events” or ‘‘looking forward to the future.” Clearly, we cannot literally lookback or forward in time (Martin, 2001). We cannot see the future or the past in the same way as we see an event unfoldingin front of us or behind us. The best we can do to capture past or future experiences of an event is to re-experience the event(retrospection), or imagine experiencing a future event (prospection).1

The ability to retrospect in this sense has become a central feature for episodic memory with Tulving’s (1985) introduc-tion of ‘‘autonoetic consciousness”, namely the awareness that remembering consists of ‘‘calling back into consciousness aseemingly lost state that is then ‘immediately recognized as something formerly experienced’ (Ebbinghaus, 1885, p. 1).” Phi-losophers spoke of ‘‘experiential memory,” at least since Locke (Owens, 1996). Although the different terms all capture thephenomenon adequately, and ‘‘retrospection” does so in nice juxtaposition to ‘‘prospection,” we prefer ‘‘episodic remember-ing” as our standard term. The choice of ‘‘remembering”, rather than ‘‘memory” is to emphasise that it is more than just

nal on Self, Other and Memory.

.to point out that the precise form of how the future is addressed in different prospection studies varies.t (e.g., on the way to the puzzle room I have to think taking the needed implement with me; Suddendorf &suffices that one can treat as placed in the future (e.g., When(-ever) I go to a hibernal resort (tomorrow) Ieltzoff, 2005). In both cases the events one imagines experiencing (into which one projects oneself) are

the puzzle, it is not a fact that one will) in contrast to retrospection, where one re-experiences (projectsce. By precedent and due to this commonality we keep using the term ‘‘prospection” for experiencing

xperiencing actual events.

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retrieval of knowledge about a past episode. It is a re-experiencing of that episode. This distinction is also brought out by thenotion of ‘‘mental time travel” (MTT: Suddendorf & Corballis, 1997; Wheeler, Stuss, & Tulving, 1997): one has to not justretrieve information about the past or think about the likely future. It requires projecting oneself as an experiencing agentinto the past or future. This distinction is also akin to the difference between having a theory of mind (Churchland, 1984;Gopnik & Astington, 1988) as opposed to simulating one’s own (or other people’s) mental processes (Goldman, 2006; Gor-don, 1986; Heal, 1986).

There is the strong and widespread, but not uncontested, intuition that these three abilities, theory of mind, episodicremembering, and prospection belong together. They may be uniquely human abilities (Gilbert & Wilson, 2007; Roberts,2002; Roberts et al., 2008; Suddendorf & Busby, 2003; Suddendorf & Corballis, 1997, 2007; Wheeler et al., 1997). There isnow also fast growing empirical evidence from different quarters that episodic remembering (often investigated underthe label or as part of autobiographical memory), prospection, and theory of mind share a developmental schedule, and com-mon neural substrate as shown in coactivation patterns and in common deficits in clinical cases.

1.1. Brain imaging

Spreng, Mar, and Kim (2008) meta-analyzed, among other areas, all available brain imaging studies on theory of mind(n = 30, as a random selection of 50), autobiographical memory (n = 19), and prospection (n = 6). Direct overlap was observedin the medial temporal lobe (left parahypocampal gyrus: BA 36), medial parietal regions (precuneus, posterior cingulate,bilaterally: BA 31), left temporo-parietal junction (BA 39, touching on BA 19), medial prefrontal cortex (frontal pole: BA10). Convergence within same Brodmann areas were also observed in right TPJ, left ventrolateral prefrontal cortex (BA47), medial prefrontal cortex, and rostral anterior cingulate (BA 32), and lateral temporal lobe (BA 21, 22) especially left.All these regions tend to also be activated by navigation problems and default processing (areas that tend to be morestrongly activated in the absence than in the presence of external stimulation). Two theories have been proposed as tothe common denominator underlying these common activations. Hassabis and Maguire (2007) suggested that all these tasksrequire scene-construction and Buckner and Carroll (2007) that they all require projection of self into different time points orspatial locations.

1.2. Brain injury

Patients without autonoetic consciousness in Tulving’s sense, i.e., amnesics with a special impairment of episodic remem-bering and autobiographical memory, have been reported to also have severe deficits of prospection, Patients K.C. (Tulving,1985), R. (Stuss, 1991), M.L. (Levine et al., 1998), and D.B. (Klein, Loftus, & Kihlstrom, 2002). Loss of autonoetic consciousnessdoes, however, not lead inevitably to an impairment in theory of mind (patients K.C. and M.L.: Rosenbaum, Stuss, Levine, &Tulving, 2007). This finding does not preclude theory of mind being necessary for autonoetic consciousness and episodicremembering, in particular, it may be crucial as a developmental requirement or linkage. In fact, there is growing evidencethat theory of mind development around 4 and 5 years is linked to both, episodic remembering as well as prospection.

1.3. Development

There are studies showing a specific relationship between advances in theory of mind and free recall as a measure of epi-sodic remembering in relation to cued recall (Tulving, 1985). Perner and Ruffman (1995) were able to show that between 3and 5 years, children’s improvement on free recall correlates significantly with their understanding of how knowledge de-pends on experience. Even when cued recall and verbal intelligence were partialled out, correlations stayed above .30. Tasksused included children’s ability to explain why they know the contents of a box (How-do-you-know test: Wimmer, Hogrefe,& Perner, 1988a; Wimmer, Hogrefe, & Sodian, 1988b), to distinguish a lucky guess from proper knowledge (Miscione, Mar-vin, O’Brien, & Greenberg, 1978), and to understand which sense modality to use to find out about colour or weight of anobject (O’Neill et al., 1992). These results were largely replicated by Naito (2003) on a Japanese sample. She also found a rela-tionship between free recall and children’s ability to understand when they had learned a fact (Taylor, Esbensen, & Bennett,1994).

Perner, Kloo, and Gornik (2007) used a different measure of episodic remembering. They contrasted recall of experiencedevents with recall of indirectly conveyed events. In the experience condition children put cards with drawings of simple ob-jects into a box. In the indirect-information condition they were blindfolded and so could not see which cards they put in-side. They were afterwards shown on a monitor the pictures that were on these cards (information about individual cardswas thus indirectly conveyed). The reasoning was that children can have an episodic memory of putting a particular cardinside the box only when they experienced putting that card into the box. Only with this experience can they later re-expe-rience their action. When blindfolded, they cannot experience which card they had put inside. When later shown what wason these cards, they can only infer that they put that card inside the box. Hence there is no experience of putting that cardinside, which they could re-experience. Free recall of experienced events correlated with performance on various theory ofmind tasks (How-do-you-know, When-did-you-learn, and the modality-specificity test). Sprung (2008) and Sprung and Har-ris (2009) found that theory of mind abilities (especially introspective understanding) modulates children’s ability to report

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on their intrusive thoughts, which in case of traumatic experiences (e.g., Hurricane Katrina victims) provides a basis for out-growing the trauma.

Rapidly growing evidence suggests that children’s prospective abilities develop at about the same age. Moore, Barresi, andThompson (1998, Experiment 1) reported some correlations between 3- and 4-year-old children’s understanding of desireand belief and of the benefits of increased but delayed reward.

Bischof-Köhler (2000) investigated several abilities in a group of 3- to 4.5-year-olds with a large battery of tasks includingunderstanding of duration, theory of mind (false belief and deception), planning (shopping, need for preparation), delay ofgratification, and motivational conflict. These abilities all underwent a noticeable improvement from 3 to 4.5 years and cor-related significantly even when children’s age was partialled out.

Atance and O’Neill (2005) investigated 3- to 4-year-olds’ ability to think about what to pack for a trip. About half of thesechildren went beyond packing typical (scripted) or attractive things. They also thought of providing for possible eventualities(e.g., pack telephone to contact someone in case of an emergency). In another task children were given the beginning of adrawing, e.g., a straight line, and then were asked what they wanted to draw on the basis of this first element. There wasa strong correlation r = .65 between children’s ability to anticipate events in the trip task and their choice of a drawing thatwas feasible with the given element (e.g., a sun but not a ladder starting from a circle) even when language ability wascontrolled.

Atance and Meltzoff (2005) tested for mental time travel and found that 3 year olds above chance chose a suitable item(e.g., winter coat) for going to a snowy place (as shown in a photograph) and they were able to explain their choice by ref-erence to their future need created by that environment. By 4 and 5 years all children could do this. It remains unclearwhether this shows children’s ability to project themselves into the future state of going to a wintery landscape. They mightjust know about the need for winter coats in a cold environment. Atance and Meltzoff (2006) overly satiated children on saltypretzels, which made them change their preference from pretzels to water. Even 5 year old children showed little sign ofunderstanding that the next day their preference would return to pretzels. They predicted a lasting preference for water.

Busby and Suddendorf (2005) simply asked 3- to 5-year-old children what they had done yesterday and what they werelikely to do tomorrow. Discounting general, scripted answers (e.g., ‘‘I played”) there was a marked improvement in children’sability to report past and likely future episodes. Suddendorf and Nielsen (2009) tested 3- and 4-year-olds on a simple prob-lem (e.g., use a triangular key to open a box). When the key was not available children went to another room and played for15 min. Before returning to the first room they were given the choice among three different keys (one triangular) and askedwhich one they would like to bring with them to the room. Three-year-olds chose at random, while 4-year-olds chose thetriangular key above chance (with plenty of room for improvement).

Atance and Jackson (2009) assessed different aspects of future thinking in 3- to 5-year-old preschoolers, includingmental time travel (Atance & Meltzoff, 2005; Busby & Suddendorf, 2005), delay of gratification, planning (simple versionof Tower of Hanoi, Carlson, Moses, & Claxton, 2004), and prospective memory (remembering to do something after fin-ishing something else: Kvavilashvili, Messer, & Ebdon, 2001). Children improved on all these tasks and performance be-tween all tasks was correlated but correlations were dependent on age and receptive vocabulary. Ford, Shum, and Driscoll(2009) found that prospective memory performance in 4- to 6-year-olds was related to inhibitory ability and understand-ing false beliefs.

Finally, Russell, Alexis, and Clayton (2010) let 3–5 year old children play blow-football for which one needed to bring astraw for blowing and as player on the blue (as opposed to the red) side a box to stand on as that side of the table was other-wise too high for children at this age. Children were asked questions framed in the past, present and future about what theythemselves or another child needed to play on the blue side. The variable was whether they thought of both required itemsor not. In case children gave different answers for themselves than for their peer, the authors reasoned, this is a likely signthat children bring to bear their own perspective when imagining how they had played, or were going to play, i.e., projectthemselves into the role of player. Systematic comparison of self and other was only carried out for present (Experiment 4)and future (Experiments 2 and 3). In particular, 4-year-olds gave similar answers for self and other in the present and forother in the future, but ignored their own needs for the future. This was interpreted as evidence that between 3 and 5 yearschildren become able to project themselves into future situations. Supportive evidence for this age trend comes from Pren-cipe and Zelazo (2005), who found that 3 year olds make wise choices of delaying an immediate small reward for a larger onelater when choosing for another person but not for themselves. This discrepancy ceases around 4 years.

1.4. Autism

The spectrum of autism consists of a developmental disorder that affects the very triad of theory of mind, retrospection,and prospection. Children with autism spectrum disorder tend to have problems with basic theory of mind tasks (Baron-Co-hen, Leslie, & Frith, 1985; Perner, Frith, Leslie, & Leekam, 1989) or the least impaired cases (Asperger’s syndrome) have def-icits appreciating subtle mental interactions like sarcasm, jokes, etc. (Happé, 1994). They also have executive deficits(Ozonoff, Pennington, & Rogers, 1991; for a review, see, Hill, 2004), which tend to be more pronounced for planning (pro-spection) than for inhibition. When tested for memory their free recall seems to be specifically impaired over cued recalland recognition (Boucher & Lewis, 1989; Boucher & Warrington, 1976; Bowler, Gardiner, & Grice, 2000; Tager-Flusberg,1991) and even the highest functioning individuals with Asperger syndrome give fewer ‘‘remember” judgments in recogni-tion tasks (Bowler, Gardiner, & Gaigg, 2007) than unimpaired people.

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1.5. Sharpening the issues

The neurophysiological and developmental evidence leaves little doubt that there is some common ground for theory ofmind, episodic remembering and prospective abilities. Whether the co-emergence of these different abilities and their shar-ing of common cerebral structures is good evidence for mental time travel, i.e., for the ability to re- and pre-experience pastor future events as the common basis remains an open question. The evidence for that claim is weak in two respects: few ofthe reviewed studies attempt to isolate specific cases of episodic remembering (retrospection: re-experiencing a past situa-tion by projecting oneself into the past) as opposed to merely retrieving knowledge about the past, and of projecting oneselfinto a future experience (prospection) as opposed to knowing what is likely to happen in the future or knowing what isneeded in an imagined future situation. Consequently, the developmental synchrony could easily be explained by quite gen-eral features, e.g., thinking about the past and future.

The contrast between free and cued recall does provide some measure for teasing out the retrospective aspects of mem-ory. Its usefulness is based on Tulving’s (1985) argument that free recall is more dependent on the availability of episodictraces than is cued recall. Hence, if free recall correlates specifically with progress in theory of mind when controlling forcued recall, then that correlation ought to be due to changes in episodic remembering (Perner, 1990) and not some moregeneral ability to think about or retrieve information about the past. The link between free recall and episodic remembering,one has to admit, is rather weak. Free recall does not depend completely on episodic remembering (even in free recall a fewitems can come to mind automatically). Moreover, free recall is not exclusively helped by episodic remembering, which canalso enhance cued recall. The contrast between memory of experienced events and indirectly conveyed events (Perner et al.,2007) is somewhat sharper in this respect. It takes advantage of the fact that only experienced events can possibly be re-experienced. Indirectly conveyed events should, therefore, not profit at all from the developing ability to rememberepisodically.

The self-other contrast used by Russell et al. (2010) helps isolate the prospective aspects of anticipating future needs. Italso allows for projection into the past, unfortunately, not for remembering any past event but only for figuring out what wasneeded for a past action as can be seen from their example test question: ‘‘. . . point to the two things you think the little girlhad to have to play blow-football on the blue side?” (Section 2.1.3). Even for prospection this method depends on the riskybackground assumption that the difference between predicting one’s own future needs and predicting someone else’s futureneeds reflects an inability of projection, which is primarily applicable to oneself and not to others. For believers in simulationtheory projection is also applied in the case of others. More generally, the difference can be due to factors that tend to inter-fere more strongly in the case of self than other.

In sum, the claim for a specific developmental relationship between the ability to retrospect (episodic remembering) andprospection rests on evidence that can be given a more general interpretation (e.g., thinking about different times) or fails toprovide the needed correlations: Perner and Ruffman (1995), Naito (2003) and Perner et al. (2007) only provide evidence forretrospection and ToM but not prospection. Russell et al. only provide evidence for prospection. Our prime objective is toprovide evidence for a specific developmental relationship between retrospection (episodic remembering) and prospection.

To capture retrospection we use the free-cued recall contrast in our first experiment and the experienced-indirectly con-veyed contrast in our second experiment. For measuring children’s prospective abilities (the study by Russell et al. was pub-lished well after our research was conceived and conducted) we relied on children’s ability to engage in mental rotation. Weused the child appropriate simplification by Estes (1998) of the original tasks by Shepard and Metzler (1971). Children wereshown pairs of teddy bears (monkeys in Estes’ original study) with one arm raised. Children had to judge whether the mon-keys had raised the same side arm (e.g., both their left arm) or an arm on different sides (one left the other right). This is easyif the creatures stand side by side but increasingly difficult if one of them is rotated sideways (see Fig. 1). An easy solution isto take the tilted picture and rotate it back to upright. However, children are not allowed to do this physically. In that caseone can rotate it mentally by forming an image of what one sees and rotate the image and then compare the rotated image ofthe tilted figure with the perception of the other figure. This procedure is an instance of prospection: one pre-experiences anactual rotation of the tilted figure. And the reaction times tell us whether a child used this method because mental rotationresults in a linear increase of reaction time with the degree of rotation (Shepard & Metzler, 1971). Estes (1998) reported thatchildren start using this method between 4 and 6 years.

Fig. 1. Examples of stimuli used for the mental rotation task in both experiments.

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2. Experiment 1

2.1. Method

2.1.1. ParticipantsFifty-nine children (25 girls and 34 boys) participated in the study. Children came from a nursery school in Upper

Austria and two after-school care clubs, one in the city of Salzburg and one in Upper Austria. Most participants camefrom a middle-class background. Children’s ages ranged from 4, 11 (years, months) to 8, 7 (M = 6, 8, SD = 13.67 months).

To analyze and display age trends, we divided the children into three approximately same sized age-groups: Twenty chil-dren from 4, 11 to 6, 0 (M = 5, 5, SD = 3.99 months), 17 children ranging in age from 6, 1 to 7, 4 (M = 6, 8, SD = 5.51 months),and 22 children ranging in age from 7, 5 to 8, 7 (M = 7, 11 SD = 4.4 months).

2.1.2. DesignEach child was tested individually in a quiet room of the nursery school or after-school care club. Children were given two

memory tasks (one with free and one with cued recall). In addition, children received a computerized mental rotation taskbased on Estes (1998) and an age-appropriate measure of verbal intelligence (verbal subtest of KISTE, Häuser, Kasielke, &Scheidereiter, 1994; or HAWIK-III, Tewes, Rossmann, & Schallberger, 1999).

All tasks were administered in two sessions a few days apart. Each session started with presentation of items for thememory task and ended with recall of memory items. Between presentation and recall of memory items, half of the chil-dren were given the mental rotation task in the first session and the verbal intelligence measure in the second session;the other half received these tasks in the opposite order. Half of the children received the free recall task in the firstsession and the cued recall task in the second session; the other half started with the cued recall task.

2.1.3. Procedure and materials2.1.3.1. Mental rotation task (Estes, 1998). In a warm-up phase, children were presented with an odd one out game. They wereshown three bears in upright position (two of them both raising the same arm and one of them raising a different arm). Chil-dren were asked to select the bear that was different from the other two.

Then, children were asked to play a computerized mental rotation task presented on a notebook computer using the soft-ware package Presentation (Neurobehavioral Systems Inc., http://www.neuro-bs.com). Children were told to press the but-ton with the smiling face if two bears both raising the same arm appeared on the screen and to press the button with the sadface if two bears each raising a different arm appeared.

After experimenter and child had jointly completed six training trials, children were asked to play on their own. The testphase comprised 56 trials. Each trial consisted of a pair of bears. The bear on the left was always upright, whereas the bear onthe right appeared in seven different orientations. He was either upright (i.e., 0� rotation) or rotated clockwise in 30� incre-ments up to 180�. In addition, each bear raised one of his arms. For half of the trials, both bears raised the same arm (i.e. bothright or both left). For the other half of trials, the bears raised different arms (i.e. the left bear raised its right arm and the rightbear raised its left arm, or the reverse). In total, there were 28 different stimulus pairs: two ‘‘same” and two ‘‘different” pairsfor each of the seven different orientations. Each child was given these 28 different stimulus pairs twice in a fixed randomorder. After the first 28 trials, there was a short 2 min break.

Children had to press as fast as possible the button marked with a smiling face if the two bears had raised their same sidearm and the button marked with a sad face if the bears had raised different side arms. Children had to keep their index fin-gers positioned on the response buttons throughout the trial block. Children were asked if they were ready before the exper-imenter initiated the next trial. Correct responses were followed by a brief tune, errors by silence. No other feedback wasgiven. After Trials 5, 28, and 56, children were asked how they could tell if the two bears had raised their same arms ornot. Sample stimuli are shown in Fig. 1.

2.1.3.2. Memory tasks. For the memory tasks two sets of 20 coloured pictures (21 � 29.7 cm) of familiar objects or animalswere created (similar to Perner & Ruffman, 1995, Exp. 1). Each set comprised five categories, with four items in each category(see Appendix A for list of items). Pictures were presented in a fixed random order. Each child received both sets. Half of thechildren were given Set 1 for the free recall task and Set 2 for the cued recall task. For the other half the two sets wereexchanged.

Children were told to look carefully at each picture they are going to see, because they will be asked about them later.Each picture was shown for 5 s and the child had to name it. Slight misidentifications (e.g., calling the farm a barn) wereaccepted. Completely wrong answers were corrected.

After the intervening task (mental rotation or verbal intelligence measure), children were reminded: ‘‘I’ve shown yousome pictures earlier on. Can you remember?” In the free recall condition, children were then simply asked ‘‘What was inthese pictures?” In the cued recall condition, they were asked for each category, e.g.: ‘‘There were some animals, what werethey?”

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The number of correctly recalled items and of false alarms (items that had not been on the learning list) were recorded.The difference between the number of correct recalls and the number of false alarms was used as a measure of recallaccuracy.

2.2. Results and discussion

First, children’s performance on the memory tasks and on the mental rotation task was analyzed separately, and then welooked at the relationship between these tasks.

2.2.1. Memory tasksRecall accuracy (hits minus false alarms) on the two memory tasks was analyzed by an analysis of variance with age-

group (younger, middle, older) as between participants factor and recall (free, cued) as a within participants factor. Therewas a significant main effect of recall, F(1, 56) = 49.61, p < .001, partial g2 = .47. No other effect was significant p > .50. Cor-relation between free and cued recall accuracy was r = .17, p > .19.

2.2.2. Mental rotationWe first looked at children’s number of correct answers. There was a clear bimodal distribution. One group of 24 children

had values from 24 to 38 normally distributed around the mean of 30.21 correct, which is just two items more than theguessing level of 28 (of 56 items): t(23) = 3.35, p < .003. Presumably these are the children who did not resort to rotation,without which they could only judge about two items consistently correctly. There were no children with values 39–41and the remaining 35 children attained values from 42 to 55 with a mean of 49.89 correct.

To see how children managed to give correct answers they were classified as rotators or non-rotators according to the twocriteria used by Estes (1998). For each child a regression analysis was computed for the median reaction times for each angleas dependent and angle of rotation as independent variable. When the regression coefficient (slope) was significantly differ-ent from zero the child was classified as a ‘‘rotator according to RT”. Children were also asked at the end how they had ap-proached the task. If they indicated that they had rotated the stimuli in their mind (e.g., ‘‘I rotated the bear in my head”) theywere classified as ‘‘rotators according to explanation”. The other children gave no insightful answer (e.g., ‘‘I just know it”).Correlation of these measures with the number correct solutions showed r = .64 for explanation, r = .66 for reaction time,and r = .67 for rotation by reaction time and explanation. We use this binary classification as ‘‘rotators” (rotators by RTand by explanation) vs. ‘‘non-rotators” for all further computations (we checked that the interpretations stay the same ifanyone of the other two is used). This way of classifying children into rotators and non-rotators had a marginally significantrelation with age (r = .25, p = .052) but a clear relationship with verbal intelligence (r = .40, p = .002).

2.2.3. Interrelations between retrospection and prospectionThe argument about the relationship between type of recall and episodic remembering is that both kinds are (can be)

helped by the availability of episodic traces. This can be equally strong, so that no interactive effect of the availability of epi-sodic traces on free vs. cued recall can be expected. However, free recall is more dependent on episodic traces than cued re-call (which profits to a large degree from the availability of the cues). Availability of episodic traces should, therefore,correlate more strongly with free than with cued recall, since more alternative factors influence cued than free recall. Thetheoretical claim is that the ability for episodic remembering requires the ability to project oneself into the past and thatthe same projective ability is required in the mental rotation task by projecting oneself as an observer of a future or hypo-thetical action (rotating one of the items to be compared). On those grounds we expect that mental rotation should show asignificant correlation with free recall even when any correlation with cued recall has been partialled out.

Table 1 shows the correlations between relevant variables in the upper right corner above the main diagonal. Partial cor-relations with age and verbal intelligence taken into account are shown for the remaining variables in italics below the maindiagonal. The correlation between rotation and free recall remains at least marginally significant but the correlation betweenrotation and cued recall reaches only about half its size. More importantly, when cued recall is partialled out the partial

Table 1Correlations and partial correlations with age and verbal intelligence controlled.

1 2 3 4 5

1. Age – .17 .25+ .10 .182. Verbal intelligence – .40** .29* .39**

3. Mental rotation – .35** .29*

4. Free recall: accuracy .26+ – .175. Cued recall: accuracy .14 .06 –

Note: Numbers in italics – partial correlations after partialling out age and verbal intelligence.+ p < .06.* p < .05.

** p < .01.

808 J. Perner et al. / Consciousness and Cognition 19 (2010) 802–815

correlation of rotation with free recall remains clearly significant (pr = .31, p = .016). This is as predicted when retrospection(as measured by free recall beyond cued recall) is developmentally linked with prospection (as measured by mentalrotation). In contrast, when free recall is partialled out the partial correlation of rotation with cued recall is weaker but doesstay marginally significant (pr = .25, p = .06), which attests to the fact, pointed out earlier, that both free and cued recall profitfrom the ability of episodic remembering to project oneself back into the past. This highlights the need for a more discerningmeasure of episodic remembering in the next experiment.

3. Experiment 2

Experiment 1 provided some evidence that the development of prospection, assessed by the ability to engage in mental rota-tion, is specifically linked to retrospection (free recall) when controlling for general ability to retrieve information about the past(cued recall). The differential performance on free over cued recall is a very weak measure of episodic remembering (retrospec-tion) since both types of recall can benefit to equal amounts from the availability of episodic traces. The only difference is thatthe overall variance of free recall should be more strongly dominated by episodic abilities than the variance of cued recall. Thisweakness is also reflected in the controversy over Tulving’s (1985) claim that relatively more items recalled in free recall shouldbe judged as ‘‘remembered” than in cued recall (Jones & Roediger, 1995; Roediger & McDermott, 1995; vs. Hamilton & Rajaram,2003).

In this second experiment we try to get stronger evidence for a specific developmental link by employing a contrast thatdepends more directly on the availability of episodic traces. A suitable contrast is between (directly) experienced events andevents about which one was indirectly informed (e.g., through verbal or pictorial media). Only experienced events can be re-experienced. Though imagined experiences can be mistaken for re-experiences (false memories) this should be relativelyrare if children are not instructed to vividly imagine the event about which they are indirectly informed. Under these pre-mises we can predict that development of retrospective abilities (episodic remembering) should uniquely improve recall ofexperienced events but not at all (except for the occasional false memory) recall of indirectly conveyed events. Following themethod used by Perner et al. (2007) we had children put cards with different pictures into a box. In the direct-experiencecondition the children saw the picture on each card as they put it into the box. In the indirect-information condition theyput the cards into the box when being blindfold and afterwards they were shown on a monitor the pictures on those cards.We expect that children’s ability to engage in mental rotation should coincide with improved recall of directly experienceditems but not of indirectly conveyed items.

3.1. Method

3.1.1. ParticipantsThirty-one children (16 girls and 15 boys) from two nursery schools in towns near the city of Salzburg participated in the

study. Most participants came from a middle-class background. Children’s ages ranged from 5, 0 (years, months) to 6, 4(M = 5, 10; SD = 4.72 months). For later analysis children were divided into a younger (n = 13, M = 5, 5; ranging from 5, 0to 5, 10) and an older group (n = 18, M = 6, 1; ranging from 5, 11 to 6, 4).

3.1.2. 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 with indirect information). In addition, children received the mental rotation task based on Estes(1998) described in Experiment 1. All tasks were administered in three sessions a few days apart. In the first session, childrenreceived the mental rotation task and a modality-specificity task in counterbalanced order.2 In the second and third session,one of the two memory tasks was given. In each session, presentation and recall of memory items were separated by a 10-mindelay. Half of the children started with the direct-experience condition and were then given the indirect-information condition.For the other half, the order was reversed.

3.1.3. Procedure and materialsThe mental rotation task (Estes, 1998) was administered as described in Experiment 1.

3.1.3.1. Memory tasks. For the memory tasks, four sets of 12 coloured pictures (21 � 29.7 cm) of familiar objects, animals, orhuman beings were used. Set 1 and Set 2 were administered in the first session. Set 3 and Set 4 were given in the secondsession. In each session, half of the children were given a particular set as test items and the other set as distractor items.For the other half, the two sets were exchanged, so that each set was equally often used as test or distractor set in the directexperience and in the indirect-information memory task.

The experimenter presented the 24 pictures (test and distractor items), one after the other, alternating between itemsfrom each set. As each picture was produced, the child was asked to name it. If necessary (which was rarely the case),the experimenter provided the correct label.

2 This task was included to make good use of the retention time. It was part of a project of a student who helped testing the children. This task will not befurther analysed.

J. Perner et al. / Consciousness and Cognition 19 (2010) 802–815 809

In the direct-experience memory task, children were then asked to place the 12 test items into a (26 � 40 � 4 cm) box. Theywere allowed to look at each picture for 2 s and were instructed to keep these pictures in mind. In the indirect-informationmemory task, children were also asked to place the 12 test items into a box but they were blindfolded so that they could notsee the pictures. After having placed the 12 items into the box, they were shown ‘‘what these 12 pictures had depicted” bymeans of a computerized presentation. Each picture was shown for two seconds, and children were instructed to keep thesepictures in mind. After a 10-min delay, children were asked in both memory tasks, ‘‘Do you remember the pictures you putinto the box?” If children answered with an item that was not put inside the box it was scored as a false alarm.

On both memory tasks, the number of correct recalls (hits) and the number of false alarms (if children mentioned itemsthat were not put inside the box) were recorded. Mostly, false alarms comprised items from the distractor set used in thefamiliarization phase. The distractor set was introduced to get a more precise measure of remembering the pictures beingput into the box as opposed to mere familiarity with the pictures. The contrast between recall of items placed inside thebox with false alarms (mostly items that children were familiarized with but did not put inside) sharpens the detectionof episodic memories in contrast to mere familiarity answers. For instance, a child who recalls two correct items and no dis-tractors is comparable with one who recalls 12 targets and 10 distractors. Both children vastly differ in recall of familiaritems (pictures) but are similar in terms of memory for items placed inside the box. This is critical, because our manipulationof direct experience and indirect knowledge pertains to the placing of cards into the box, not to familiarity with the pictures(they are directly experienced in both conditions). For this reason it is essential to rely not only on the quantity of picturesrecalled (number of placed pictures recalled in relation to all pictures placed into the box) but also check for accuracy (num-ber of placed pictures recalled in relation to all pictures recalled; as this terminology is used by Koriat and Goldsmith (1996,p. 177)). A measure that captures both these aspects common in signal detection theory is d0 which is based on the differencebetween hits and false alarms. This is typical for forced choice recognition tasks and rarely used with recall (Koriat & Gold-smith, 1996, p. 183). Following this approach, we use the difference between number correct items recalled minus numberfalse alarms as our critical indicator of episodic recall and refer to it, for want of a shorter label and in line with signal detec-tion theory, as: recall accuracy.

3.2. Results

First, children’s performance on the memory tasks and on the mental rotation task was analyzed separately, and then welooked at the relationship between these tasks.

3.2.1. Memory tasksRecall accuracy (hits minus false alarms) was subjected to an analysis of variance with age-group as between participants

factor and experience (direct, indirect) as a within participants factor. There was a significant interaction between age-groupand experience, F(1, 29) = 4.31, p < .047, partial g2 = .13. Whereas the recall of directly experienced items increased with agefrom 2.69 to 3.56 items, recall of indirect items declined with age from 3.46 to 2.50 items. This unexpected decline will bediscussed below when looking at the relationship with mental rotation (prospection). No other effect was significant p > .70.Correlation between direct and indirect recall accuracy was r = .42, p = .019.

3.2.2. Mental rotationThe results mirror those of Experiment 1. The numbers of correct answers range from 28 to 54. There was again a strong

correlation (r = .57, p = .001) between number correct solutions and rotation by explanation (r = .38, p = .033), rotation byreaction time (r = .46, p = .01), and rotation by reaction and explanation (r = .58, p = .001). As in Experiment 1 we use rotationby reaction time and explanation for our further analyses. This classification had a marginal correlation with age in Exper-iment 1 but this time it had no correlation with age at all (r = .00), which is probably due to the much narrower age range inthis experiment.

3.2.3. The relation between retrospection and prospectionThe contrast between directly experienced versus indirectly conveyed events works differently than the contrast between

free and cued recall in Experiment 1. While free and cued recall can profit from episodic remembering, only directly expe-rienced events can do so, because only experienced events can be re-experienced. This means that the emerging ability forepisodic remembering should enhance recall of directly experienced events but not recall of indirectly conveyed events.Moreover, re-experiencing past events (episodic remembering) and pre-experiencing imagined events for mental rotationrequire the same ability of projecting oneself as an observer. Hence, we expect that children who can use mental rotationwill have better recall of directly experienced events than of indirectly conveyed events. Children, who fail to use rotation,will show no, or at least a much reduced, difference in recall.

An analysis of variance of recall accuracy (number of hits minus false alarms) with rotation (rotation by RT and explana-tion: rotators vs. non-rotators) as a between subjects factor and experience (experienced vs. indirectly conveyed events)showed significant main effects of rotation (F(1, 29) = 5.16, p = .031, partial g2 = .15) and experience (F(1, 29) = 4.51,p = .042, partial g2 = .13), and a highly significant rotation � experience interaction (F(1, 29) = 7.83, p = .009, partialg2 = .21). This interaction was predicted. However, the form of the interaction as displayed in the left panel of Fig. 2 harbours

Fig. 2. Results for rotators and non-rotators on three different memory measures in Experiment 2.

810 J. Perner et al. / Consciousness and Cognition 19 (2010) 802–815

a surprise. The ability to mentally rotate does not lead to enhanced memory for experienced events but has a detrimentaleffect on trying to remember indirectly conveyed events.

This decline in accuracy for indirectly conveyed events persists for rotators-by-RT but not for rotators-by-explanation(p = .016), although the pattern of results is still very similar. This sharp decline (by 3.2 items) in accuracy (hits minus falsealarms) is, as the centre panel in Fig. 2 shows, less pronounced (1.6 items) for hits (items correctly recalled) but still signif-icant (interaction: (F(1, 29) = 4.81, p = .037, partial g2 = .14)). At the same time the number of false alarms increases moresharply for indirectly conveyed items than experienced items (F(1, 29) = 4.45, p = .045, partial g2 = .13) as the right panelin Fig. 2 shows.

3.3. Discussion

The ability to engage in mental rotation had a strong differential effect on children’s ability to recall directly experiencedevents and to recall indirectly conveyed events. The finding, however, contained a great surprise: the differential effect didnot consist in rotators’ better recall of experienced events but was due to their worse recall of indirectly conveyed events.This unexpected decline in recall of indirectly conveyed items does, nevertheless, confirm a trend observed in two experi-ments by Perner et al. (2007), where recall of indirectly conveyed items declined with increased theory of mind competence.What seemed initially a curious and haphazard finding now looks increasingly robust: As children improve their theory ofmind and develop mental rotation skills their recall of indirectly conveyed information declines.

It is difficult to find an obvious explanation for this decline. One could suspect that the reason lies in the unusual proce-dure of the indirect condition. But why should the more sophisticated rotators become confused by this procedure, whenadults find it unusual but clear and perform as well as in the more normal experience condition (Stöttinger, 2006). The onlyplausible but highly speculative explanation has been briefly alluded to by Perner et al. (2007, p. 480). The younger childrenuse their non-episodic recall (knowledge retrieval) for both conditions more or less successfully. Then when their theory ofmind competence increases and become able to project themselves as past perceivers of experienced events they switch tousing episodic recall. This switch may (Perner et al., 2007) or may not (current Experiment 2) help them immediately to re-call more items than with non-episodic recall. In any case, this switch does not work for indirectly conveyed items and chil-dren’s performance declines. Presumably some time after discovering episodic recall children will realize that it does notwork in every case and will readjust their strategy for indirect information.

Eventually they may also discover the possibility of indirect episodic recall for indirect information. That is, when toldabout an event they should not try to re-experience (episodically remember) the event (e.g., putting the crocodile intothe box) but to remember the information event (i.e., remember the crocodile appearing on the monitor and the instruc-tions that pictures on the monitor were on the cards put inside the box). It is left to future studies to explore thisdevelopment.

4. General discussion

We have presented some data showing that prospection (as measured by children’s ability to engage in mental rotation)is related to retrospection (episodic remembering: as measured by variance shared with free recall when controlling for cuedrecall and by the difference between recall of experienced events (which can be re-experienced) versus recalling indirectlyconveyed events (which cannot be re-experienced). Our expectation was that recall of indirect information would be unaf-fected while recall of experienced events, which can be re-experienced, would increase with children’s ability to mentallyrotate.

Contrary to expectations recall of experienced events was unaffected while children’s recall of indirect informationdropped drastically with their ability to engage in mental rotation. Although, retrospectively (sic!), this trend was alreadyapparent in investigations of children’s theory of mind competence (Perner et al., 2007), the sharpness of this trend with

J. Perner et al. / Consciousness and Cognition 19 (2010) 802–815 811

mental rotation came as a surprise. The only plausible explanation we found was that acquisition of mental rotationmarks a change in recall strategy. Instead of retrieving knowledge as before, children expect to find answers by trying tore-experience the relevant events. This is a successful replacement for the old strategy in the case of experienced eventsbut fails miserably for indirect information about events. Despite these unexpected results we were able to demonstratea developmental link between retro- and prospection that is Difficult to reduce to a more general connection, e.g., under-standing time, which could account for existing data as reviewed in the Introduction.

The specific connection we identified is children’s ability to project themselves mentally as experiencing events. Thischaracterisation is commensurable with the neurocognitive suggestions of self-projection (Buckner & Carroll, 2007) andscene-construction (Hassabis & Maguire, 2007). In fact, on our view these two abilities are necessary complements: To pro-ject oneself as an observer of events at different times one has to be able to project one self into different times AND be ableto reconstruct the scenes that one is to observe.

Our results are less compatible with the ages observed in earlier developmental studies. Results from many of the studiesreviewed earlier that looked at prospection suggest that the main development takes place between 3 and 5 years, thoughnot from all studies. For instance, Atance and Meltzoff’s (2006) report that 5-year olds still could not imagine/anticipate thattheir current desire for water induced by overfeeding on salty pretzels will have reverted next day to their usual desire forpretzels. The fact that prospection as measured with mental rotation points to later development might mean that the stud-ies that see the development completed by 5 years did not assess children’s ability to project themselves as observers (exper-iencers) of events at different times but assessed their knowledge about events in the past or future.

Research on children’s retrospection (episodic remembering) also finds development in this age bracket but clearly alsopoints to improvements beyond the age of 5 years. The original studies by Perner and Ruffman (1995) and also Naito (2003)included children up to 7 years and their more difficult theory of mind tasks tended to show the stronger correlations withmeasures of episodic remembering. These findings are, therefore, more in line with the developments documented in thepresent studies.

We want to end with more general considerations about the methodological difficulties in assessing young children’s andnon-verbal creatures’ explanations and subjective phenomenology. The autonoetic awareness of re-experiencing a formerlyexperienced event is something very subjective, in the sense that evidence for it comes exclusively from introspective verbalreports. With adult participants in memory experiments the relevant experience has been assessed by the ‘‘R–K” test. Peoplehave to judge their subjective experience of recall or recognition as one of merely knowing (K) what had happened (presen-tation of an item) or remembering (R) this event. This test is less than straight forward with adults, its value highly contro-versial (Donaldson, 1996; Dunn, 2004; Gardiner & Richardson-Klavehn, 2000; Stöttinger, Aigner, Hanstein, & Perner, 2009;Stöttinger, Kaiser, & Perner, 2009) and its use for young children beyond contemplation. The only solution seems to be anobjectively measurable indicator of these subjective phenomena.

This enterprise requires a fine instrument in order to distinguish between knowing what happened and re-experiencing(remembering) the event retrospectively, and between knowing what will happen and pre-living the likely event in prospec-tion. The instrument has to be precise because both kinds of mental processes can, in principle, produce the required infor-mation about the world. They are ‘‘computationally equivalent”: both can give the correct answer to the questions posed,e.g.: What happened? Which item was presented? The difference must primarily lie in how the system arrives at the answer.Cognitive Psychology can, supposedly, provide the relevant instruments. So, no wonder that one of its most impressive find-ings, mental rotation, has such appeal in this context. The critical point is not that mental rotation can provide the correctsame–different judgments—there may be infinitely many computationally equivalent ways. It is the pattern of reactiontimes that tells us that the answer is arrived at by mental rotation as we subjectively experience it. However, even the reac-tion time pattern is not a fail safe indicator of prospection.

Several species of animals can give correct responses, e.g., pigeons, but do not show the same linear pattern of reactiontimes with angle of rotation (Hollard & Delius, 1982). Their visual system directly provides rotation invariance and they donot have to mentally simulate perceiving a hypothetical rotation. However, the reaction times of baboons (Vauclair, Fagot, &Hopkins, 1993), a sea lion (Stich, Dehnhardt, & Mauck, 2003) and a lion-tailed macacque (Burmann, Dehnhardt, & Mauck,2005) also show some signs of the linear relationship with angle of rotation, though their times deviate from the humanpattern in ways adaptive for their respective perceptual environment. For argument’s sake let us assume their reactiontimes showed exactly the same pattern. We could still not conclude that these animals project themselves as perceiversof hypothetical rotation events (mental time travel). Their visual system might provide rotation invariance but processingtime happens to depend on angle of rotation. Thus, the ultimate justification for interpreting the linear reaction time patternin humans as a sign of mental time travel hinges on the fact that this linearity goes hand in hand with the subjective expe-rience of mental rotation in adults. This relationship between observable answer and subjective experience in adults is notso tight for other measures. For instance, when asked what to pack for a trip to a place shown in a hibernal scene (Atance &Meltzoff, 2005) my answer ‘‘winter coat” could be given by projecting myself travelling to that place and noticing the needfor a winter coat. However, it could equally well be based on just knowing that in places like this you need a winter coat.Mental rotation (provided the linear reaction time pattern does indicate it) is a much less vulnerable indicator ofprospection.

For investigating episodic remembering (retrospection) in animals and young children several proposals have been made.The technically most sophisticated has been developed by Yonelinas (1999) for distinguishing between recall based on famil-

812 J. Perner et al. / Consciousness and Cognition 19 (2010) 802–815

iarity versus recollection, which can be profitably used even with rats (Sauvage, Fortin, Owens, Yonelinas, & Eichenbaum,2008). Unfortunately the distinction between familiarity of items and recollection of associative information is not quitethe same as between knowing and remembering. Associative information can be known or remembered. We need methodsthat drive a wedge between knowing the past and remembering the past. Perner and Ruffman (1995) followed Tulving’scriterion that free recall produces relatively more experiences of remembering than cued recall. Unfortunately the link tothe one direct method of assessment of the remember–know paradigm remains tenuous (Hamilton & Rajaram, 2003; Jones& Roediger, 1995; Roediger & McDermott, 1995). Perner et al. (2007); our Experiment 2) relied on an objective prerequisitefor episodic remembering, i.e., the direct experience constraint (Stöttinger, Aigner, et al. 2009; Stöttinger, Kaiser, et al., 2009):only an experienced event can be re-experienced.

Neither of these methods is apt to produce positive demonstrations of a child enjoying a re-experience of a past episode.These methods only allow an objective test of developmental hypotheses: if some other ability (theory of mind, mental rota-tion) can be claimed to index the onset of re-experiencing then the method allows for a testable prediction. The developmentof the index ability should have a differential effect on recall conditions (free vs. cued; recall of directly experienced vs. indi-rectly conveyed events).

Although the method falls short of giving a direct existence proof of episodic remembering it does provide an empiricaltest of hypotheses about episodic remembering that could also be used on animals. As it has been applied here it requiressome linguistic proficiency for the indirect-information condition. It would not work without being able to tell children thatthe items shown on the monitor are the same as on the cards they could not see. Indirect knowledge through verbal com-munication is difficult to use with animals but there are dogs (Miklósi, Polgárdi, Topál, & Csányi, 2000) and goats (Kaminski,Riedel, Call, & Tomasello, 2005), who understand pointing gestures, and there are chimpanzees who can infer from seeingthat one of two containers is empty that the object must be in the other container (Call, 2004). So, if we can find a theoryof which individuals (ontogenetic development, enculturation, evolution) are able of episodic remembering, then we canprovide testable predictions of how these individuals differ in recalling directly observed locations vs. gestured or inferredlocations.

Clayton and Russell (2009) made a new suggestion of how to differentiate knowledge of the past from remembering thepast empirically without use of language. Their minimal requirement for remembering is evidence during re-experience ofthe subjective perspective of the original experience. This is clearly a highly relevant aspect—but an important limitation hasto be pointed out. Like the direct experience constraint, this criterion cuts only one way: features of subjective perspective atrecall do not licence claims about re-experiencing. For, perspective features could result from how knowledge of the past isencoded. To use an example from Davies, Russell, and Russell (2009), children observed how to fix a toy boat by performingon a left or right lever either a pumping or levering motion. By 3 years most children imitated after some delay a series of twoconsecutive actions in the correct spatio-temporal order. The authors suggested that this shows earlier episodic remember-ing than commonly expected, because children reproduced the temporal perspective of their original experience. The prob-lem with this conclusion is that the study confounds the subjective order of experiences with the objective knowledge of theorder in which the actions were performed.

What one might be able to do is the following. Let us assume children below 3 years can remember sequences of events tosome degree. One would then have to show that at the purported age of 3 years children show a marked change in the orderin which they recall witnessed events but do not show any change in the order in which they report the events having hap-pened. This method put together with the direct experience vs. indirect information contrast (Perner et al., 2007) may pro-vide a more powerful combination. Reports of events need not follow the order of the events. So, particularly strong evidencewould be forthcoming if at the critical age children began recalling events in the order they had been reported rather thanthe order in which they happened, e.g., when told ‘‘he ate after his nap” the younger ones recall, ‘‘he slept”–‘‘he ate,” whilethe older ones recall, ‘‘he ate”–‘‘he slept”. This kind of reversal would provide an interesting analogy to our finding that rota-tors started to have problems with indirectly conveyed events because—our suggestion—they switched from knowledge re-trieval to episodic remembering.

There has been a certain resentment among animal and infancy researchers against insisting on Tulving’s (1985) andWheeler et al. (1997)) criteria for episodic memory because they seem to be impossible to meet for non- or low verbal crea-tures. With our research and this final discussion we want to make the case that to capture the phenomenon of episodicremembering we need to insist on these criteria but that there is a way of testing theories of when episodic rememberingdevelops or evolves.

Acknowledgments

The authors acknowledge the financial support from the Austrian Science Fund (FWF Grant P16215-G04 ‘‘Episodic Mem-ory and Conscious Experience”). The data of Experiment 1 were collected by Michael Rohwer for his Diploma thesis (2006)‘‘Zusammenhang zwischen episodischem Gedächtnis und mentaler Rotation.” We thank the Head and staff of the Kindergar-ten Seekirchen, Kindergarten Thalgau, Kindergarten Thalheim, Hort Taxham, and Hort Thalheim for their willing participa-tion and Elisabeth Stöttinger for her guidance through the adult memory literature.

J. Perner et al. / Consciousness and Cognition 19 (2010) 802–815 813

Appendix A

Memory items used in Experiment 1, ordered by category. Original German words (English translation)

Set 1

Set 2

Tiere (animals)

Pflanzen (plants) – Schaf (sheep)– Pferd (horse)– Schwein (pig)– Kuh (cow)

– Baum (tree)– Sonnenblume (sun flower)– Rose (rose)– Getreide/Weizen (wheat)

Gemüse (vegetables)

Obst (fruit) – Karotte (carrot)– Erbse (pea)– Zwiebel (onion)– Paprika (red pepper)

– Birne (pear)– Weintrauben (grapes)– Kirschen (cherries)– Apfel (apple)

Möbel (furniture)

Kleidung (clothes) – Bett (bed)– Tisch (table)– Stuhl (chair)– Schrank (wardrobe)

– Pullover (sweater)– Schuhe (shoes)– Socken (socks)– Hose/Jeans (trousers/Jeans)

Gebäude (buildings)

Fahrzeuge (vehicles) – Kirche (church)– Burg (castle)– Haus (house)– Scheune (barn)

– Bus (bus)– Auto (car)– Lastwagen (lorry/ truck)– Motorrad (motorbike)

Werkzeuge (tools) Musikinstrumente (musical instruments)

– Säge (saw)– Schaufel/Spaten (spade)– Zange (pliers)– Hammer (hammer)

– Trompete (trumpet)– Klavier/Piano (piano)– Geige/Violine (violin)– Trommel (drum)

References

Atance, C. M., & Jackson, L. K. (2009). The development and coherence of future-oriented behaviors during the preschool years. Journal of Experimental ChildPsychology, 102(4), 379–391.

Atance, C. M., & Meltzoff, A. N. (2005). My future self: Young children’s ability to anticipate and explain future states. Cognitive Development, 20(3), 341–361.Atance, C. M., & Meltzoff, A. N. (2006). Preschoolers’ current desires warp their choices for the future. Psychological Science, 17(7), 583–587.Atance, C. M., & O’Neill, D. K. (2005). The emergence of episodic future thinking in humans. Learning and Motivation, 36(2), 126–144.Baron-Cohen, S., Leslie, A. M., & Frith, U. (1985). Does the autistic child have a ‘‘theory of mind”? Cognition, 21, 37–46.Bischof-Köhler, D. (2000). Kinder auf Zeitreise: Theory of mind, Zeitverständnis und Handlungsorganisation. Bern ua: Hans Huber.Boucher, J., & Lewis, V. (1989). Memory impairments and communication in relatively able autistic children. Journal of Child Psychology and Psychiatry and

Allied Disciplines, 30(1), 99–122.Boucher, J., & Warrington, E. (1976). Memory deficits in early infantile autism: Some similarities to the amnesic syndrome. British Journal of Psychology, 67,

73–87.Bowler, D. M., Gardiner, J. M., & Gaigg, S. B. (2007). Factors affecting conscious awareness in the recollective experience of adults with Asperger’s syndrome.

Consciousness and Cognition, 16(1), 124–143.Bowler, D. M., Gardiner, J. M., & Grice, S. (2000). Episodic memory and remembering in adults with Asperger syndrome. Journal of Autism and Developmental

Disorders, 30, 305–316.Buckner, R. L., & Carroll, D. C. (2007). Self-projection and the brain. Trends in Cognitive Sciences, 11(2), 49–57.Burmann, B., Dehnhardt, G., & Mauck, B. (2005). Visual information processing in the lion-tailed macaque (Macaca silenus): Mental rotation or rotational

invariance? Brain, Behavior and Evolution, 65(3), 168–176.Busby, J., & Suddendorf, T. (2005). Recalling yesterday and predicting tomorrow. Cognitive Development, 20(3), 362–372.Call, J. (2004). Inferences about the location of food in the great apes (Pan paniscus, Pan troglodytes, Gorilla gorilla, and Pongo pygmaeus). Journal of

Comparative Psychology Copyright, 118, 232–241.Carlson, S. M., Moses, L. J., & Claxton, L. J. (2004). Individual differences in executive functioning and theory of mind: An investigation of inhibitory control

and planning ability. Journal of Experimental Child Psychology, 87, 299–319.Churchland, P. M. (1984). Matter and consciousness: A contemporary introduction to the philosophy of mind. Cambridge, MA: MIT Press. A Bradford book.Clayton, N. S., & Russell, J. (2009). Looking for episodic memory in animals and young children: Prospects for a new minimalism. Neuropsychologia, 47(11),

2330–2340.Davies, J., Russell, C., & Russell, J. (2009). Making deferred imitation a measure of episodic memory. Unpublished manuscript, Department of Experimental

Psychology, Cambridge University.Donaldson, W. (1996). The role of decision processes in remembering and knowing. Memory and Cognition, 24, 523–533.Dunn, J. C. (2004). Remember–know: A matter of confidence. Psychological Review, 111(2), 524–542.Ebbinghaus, H. (1885). Über das Gedächtnis. Leipzig: Duncker und Humblot.Estes, D. (1998). Young children’s awareness of their mental activity: The case of mental rotation. Child Development, 69(5), 1345–1360.

814 J. Perner et al. / Consciousness and Cognition 19 (2010) 802–815

Ford, R., Shum, D., & Driscoll, T. (2009). Event-based prospective memory in young children: An individual difference analysis. Paper presented as part of thesymposium on prospective memory at the BPS Cognitive Section 26th annual meeting, University of Hertfordshire, 1–3 September 2009.

Gardiner, J. M., & Richardson-Klavehn, A. (2000). Remembering and knowing. In E. Tulving & F. I. M. Craik (Eds.), The Oxford handbook of memory(pp. 229–244). Oxford, New York: Oxford University Press.

Gilbert, D. T., & Wilson, T. D. (2007). Prospection: Experiencing the future. Science (New York, NY), 317(5843), 1351–1354.Goldman, A. I. (2006). Simulating minds: The philosophy, psychology, and neuroscience of mindreading. Oxford: Oxford University Press.Gopnik, A., & Astington, J. W. (1988). Children’s understanding of representational change and its relation to the understanding of false belief and the

appearance-reality distinction. Child Development, 59, 26–37.Gordon, R. M. (1986). Folk psychology as simulation. Mind and Language, 1, 158–171.Hamilton, M., & Rajaram, S. (2003). States of awareness across multiple memory tasks: Obtaining a ‘‘pure” measure of conscious recollection. Acta

Psychologica, 112, 43–69.Happé, F. (1994). An advanced test of theory of mind: Understanding of story characters’ thoughts and feelings by able autistic, mentally handicapped, and

normal children and adults. Journal of Autism and Developmental Disorders, 24, 129–154.Hassabis, D., & Maguire, E. A. (2007). Deconstructing episodic memory with construction. Trends in Cognitive Sciences, 11(7), 299–306.Häuser, D., Kasielke, E., & Scheidereiter, U. (1994). Kindersprachtest für das Vorschulalter (KISTE). Bern, Göttingen: Hogrefe.Heal, J. (1986). Replication and functionalism. In J. Butterfield (Ed.), Language, mind, and logic (pp. 135–150). Cambridge: Cambridge University Press.Hill, E. L. (2004). Executive dysfunction in autism. Trends in Cognitive Sciences, 8, 26–32.Hollard, V., & Delius, J. (1982). Rotational invariance in visual pattern recognition by pigeons and humans. Science, 218(4574), 804–806.Jones, T. C., & Roediger, H. L. I. (1995). The experiential basis of serial position effects. European Journal of Cognitive Psychology, 7, 65–80.Kaminski, J., Riedel, J., Call, J., & Tomasello, M. (2005). Domestic goats, Capra hircus, follow gaze direction and use social cues in an object choice task. Animal

Behaviour, 69, 11–18.Klein, S. B., Loftus, J., & Kihlstrom, J. F. (2002). Memory and temporal experience. The effects of episodic memory loss on an amnesic patient’s ability to

remember the past and imagine the future. Social Cognition, 20, 353–379.Koriat, A., & Goldsmith, M. (1996). Memory metaphors and the real-life/laboratory controversy: Correspondence versus storehouse conceptions of memory.

Behavioral and Brain Sciences, 19, 167–228.Kvavilashvili, L., Messer, D. J., & Ebdon, P. (2001). Prospective memory in children: The effects of age and task interruption. Developmental Psychology, 37,

418–430.Levine, B., Black, S. E., Cabeza, R., Sinden, M., Mcintosh, A. R., Toth, J. P., et al (1998). Episodic memory and the self in a case of isolated retrograde amnesia.

Brain, 121(10), 1951–1973.Martin, M. G. F. (2001). Out of the past: Episodic recall as retained acquaintance. In C. Hoerl & T. McCormack (Eds.), Time and memory: Issues in philosophy

and psychology (pp. 257–284). Oxford: Clarendon Press.Miklósi, A., Polgárdi, R., Topál, J., & Csányi, V. (2000). Intentional behaviour in dog-human communication: An experimental analysis of ‘‘showing” behaviour

in the dog. Animal Cognition, 3, 159–166.Miscione, J. L., Marvin, R. S., O’Brien, R. G., & Greenberg, M. T. (1978). A developmental study of preschool children’s understanding of the words”know” and

‘‘guess”. Child Development, 49, 1107–1113.Moore, C., Barresi, J., & Thompson, C. (1998). The cognitive basis of future-oriented prosocial behavior. Social Development, 7, 198–218.Naito, M. (2003). The relationship between theory of mind and episodic memory: Evidence for the development of autonoetic consciousness. Journal of

Experimental Child Psychology, 85, 312–336.O’Neill, D. K., Astington, J. W., & Flavell, J. H. (1992). Young children’s understanding of the role that sensory experiences play in knowledge acquisition. Child

Development, 63, 474–490.Owens, D. (1996). A Lockean theory of memory experience. Philosophy and Phenomenological Research, LVI, 319–332.Ozonoff, S., Pennington, B. F., & Rogers, S. J. (1991). Executive function deficits in high-functioning autistic children: Relationship to theory of mind. Journal of

Child Psychology and Psychiatry, 32, 1081–1105.Perner, J. (1990). Experiential awareness and children’s episodic memory. In W. Schneider & F. E. Weinert (Eds.), Interactions among aptitudes, strategies, and

knowledge in cognitive performance (pp. 3–11). New York, Berlin, Heidelberg, London, Paris, Tokyo, Hong Kong: Springer-Verlag.Perner, J., Frith, U., Leslie, A. M., & Leekam, S. R. (1989). Exploration of the autistic child’s theory of mind: Knowledge, belief and communication. Child

Development, 60, 689–700.Perner, J., Kloo, D., & Gornik, E. (2007). Episodic memory development: Theory of mind is part of re-experiencing experienced events. Infant and Child

Development, 16, 471–490.Perner, J., & Ruffman, T. (1995). Episodic memory an autonoetic consciousness: Developmental evidence and a theory of childhood amnesia. Journal of

Experimental Child Psychology, 59(3), 516–548 (special issue: early memory).Prencipe, A., & Zelazo, P. D. (2005). Development of affective decision making for self and other: Evidence for the integration of first- and third-person

perspectives. Psychological Science, 16(7), 501–505.Roberts, W., Feeney, M., MacPherson, K., Petter, M., McMillan, N., & Musolino, E. (2008). Episodic-like memory in rats: Is it based on when or how long ago?

Science, 320(5872), 113–115.Roberts, W. A. (2002). Are animals stuck in time? Psychological Bulletin, 128(3), 473–489.Roediger, H. L. I., & McDermott, K. B. (1995). Creating false memories: Remembering words not presented in lists. Journal of Experimental Psychology:

Learning, Memory and Cognition, 21, 803–814.Rosenbaum, R. S., Stuss, D. T., Levine, B., & Tulving, E. (2007). Theory of mind is independent of episodic memory. Science, 318, 1257.Russell, J., Alexis, D., & Clayton, N. (2010). Episodic future thinking in 3- to 5-year-old children: The ability to think of what will be needed from a different

point of view. Cognition, 114(1), 56–71.Sauvage, M. M., Fortin, N. J., Owens, C. B., Yonelinas, A. P., & Eichenbaum, H. (2008). Recognition memory: Opposite effects of hippocampal damage on

recollection and familiarity. Nature Neuroscience, 11(1), 16–18.Shepard, R. N., & Metzler, J. (1971). Mental rotation of three-dimensional objects. Science, 171, 701–703.Spreng, R. N., Mar, R. A., & Kim, A. S. (2008). The common neural basis of autobiographical memory, prospection, navigation, theory of mind, and the default

mode: A quantitative meta-analysis. Journal of Cognitive Neuroscience, 21(3), 489–510.Sprung, M. (2008). Unwanted intrusive thoughts and cognitive functioning in kindergarten and young elementary school-age children following Hurricane

Katrina. Journal of Clinical Child and Adolescent Psychology, 37(3), 575–587.Sprung, M., & Harris, P. (2009). Intrusive thoughts and young children’s knowledge about thinking following a natural disaster. Journal of Child Psychology

and Psychiatry.Stich, K. P., Dehnhardt, G., & Mauck, B. (2003). Mental rotation of perspective stimuli in a California sea lion (Zalophus californianus). Brain, Behavior and

Evolution, 61(2), 102–112.Stöttinger, E. (2006). Episodisches Gedächtnis – Erinnern als wirkliches Wiedererleben. Unpublished thesis, University of Salzburg.Stöttinger, E., Aigner, S., Hanstein, K., & Perner, J. (2009). Grasping the diagonal: Controlling attention to illusory stimuli for action and perception.

Consciousness and Cognition, 18(1), 223–228.Stöttinger, E., Kaiser, W., & Perner, J. (2009). ‘‘Remember” judgments and the constraint of direct experience. Psychological Research – Psychologische

Forschung, 73, 623–632.Stuss, D. T. (1991). Disturbance of self-awareness after frontal system damage. In G. P. Prigatano & D. L. Schacter (Eds.), Awareness of deficit after brain injury

(pp. 63–83). Oxford: Oxford University Press.

J. Perner et al. / Consciousness and Cognition 19 (2010) 802–815 815

Suddendorf, T., & Busby, J. (2003). Like it or not? The mental time travel debate: Reply to Clayton et al.. Trends in Cognitive Sciences, 7, 437–438.Suddendorf, T., & Corballis, M. C. (1997). Mental time travel and the evolution of the human mind. Genetic, Social, and General Psychology Monographs, 123,

133–167.Suddendorf, T., & Corballis, M. C. (2007). The evolution of foresight: What is mental time travel, and is it unique to humans? The Behavioral and Brain

Sciences, 30(3), 299–313 (discussion 313-51).Suddendorf, T., Nielsen, M. (2009). The development of foresight: Children’s capacity to remember a novel problem and to secure its future solution. Unpublished

manuscript, University of Queensland.Tager-Flusberg, H. (1991). Semantic processing in the free recall of autistic children: Further evidence for a cognitive deficit. British Journal of Developmental

Psychology, 9, 417–430.Taylor, M., Esbensen, B., & Bennett, R. T. (1994). Children’s understanding of knowledge acquisition: The tendency for children to report they have always

known what they have just learned. Child Development, 65, 1581–1604.Tewes, U., Rossmann, P., & Schallberger, U. (1999). Hamburg-Wechsler-Intelligenztest für Kinder III (HAWIK-III). Handbuch und Testanweisung (3. überarbeitete

und ergänzte Auflage). Bern: Verlag Hans Huber.Tulving, E. (1985). Memory and consciousness. Canadian Psychology, 26, 1–12.Vauclair, J., Fagot, J., & Hopkins, W. D. (1993). Rotation of mental images in baboons when the visual input is directed to the left cerebral hemisphere.

Psychological Science, 4(2), 99–103.Wheeler, M. A., Stuss, D. T., & Tulving, E. (1997). Toward a theory of episodic memory: The frontal lobes and autonoetic consciousness. Psychological Bulletin,

121(3), 331–354.Wimmer, H., Hogrefe, J., & Perner, J. (1988a). Children’s understanding of informational access as source of knowledge. Child Development, 59, 386–396.Wimmer, H., Hogrefe, J., & Sodian, B. (1988b). A second stage in children’s conception of mental life: Understanding sources of information. In J. W.

Astington, P. L. Harris, & D. R. Olson (Eds.), Developing theories of mind (pp. 173–192). New York: Cambridge University Press.Yonelinas, A. P. (1999). The contribution of recollection and familiarity to recognition and source-memory judgments: A formal dual-process model and an

analysis of receiver operating characteristics. Journal of Experimental Psychology: Learning, Memory and Cognition, 25(6), 1415–1434.