1 Consciousness and Cognition 12 (2003) Consciousness and Cognition Do I get what you get? Learning about the effects of self-performed and observed actions in infancy Birgit Elsner a,b, * and Gisa Aschersleben a a Max Planck Institute for Psychological Research, Munich, Germany b Department of Psychology, University of Heidelberg, Hauptstrasse 47-51, D Heidelberg, Germany Received 28 April 2003 Abstract The present study investigated whether infants learn the effects of other personsõ actions like they do for their own actions, and whether infants transfer observed action effect relations to their own actions. Nine-, 12-, 15- and 18-month-olds explored an object that allowed two actions, and that produced a certain salient effect after each action. In a self-exploration group, infants explored the object directly, whereas in two observation groups, infants first watched an adult model acting on the object and obtaining a certain effect with each action before exploring the objects by themselves. In one observation group, the infantsõ actions were followed by the same effects as the modelõs actions, but in the other group, the action effect mapping for the infant was reversed to that of the model. The results showed that the observation of the model had an impact on the infantsõ exploration behavior from 12 months, but not earlier, and that the specific relations between observed actions and effects were acquired by 15 months. Thus, around their first birthday infants learn the effects of other personsõ actions by observation, and they transfer the observed action effect relations to their own actions in the second year of life. Ó 2003 Elsevier Inc. All rights reserved. Keywords: Imitation; Learning; Observational learning; Action effect coupling; Goal-directed actions; Action understanding; Infants 1. Introduction From the earliest days of life, infants learn to act on their environment in order to bring about desired consequences. By exploring the contingencies between self-performed movements and * Corresponding author. Fax: address: (B. Elsner) /$ - see front matter Ó 2003 Elsevier Inc. All rights reserved. doi: /s (03)
2 B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) environmental events, infants learn to predict the effects of their actions. This is important for the development of goal-directed action, in which an action must be chosen that is suitable to bring about a desired effect. Several authors (Neisser, 1991; Rochat & Striano, 2000) state that the ability to identify the environmental effects of oneõs own actions is one source of self-knowledge that is in place from early infancy. However, infantsõ learning about the consequences of selfproduced actions is constrained by motor development. Especially in the first year of life, the range of possible self-performed actions is quite narrow, so it seems unlikely that infants acquire all their knowledge about actions and their effects by individual learning. Observational learning would be an alternative way to acquire action effect knowledge. Infants spend most of their first year observing the world around them. So they have ample opportunity to watch others, like parents or siblings, acting on the environment, and they could learn about actions and their consequences by observation and imitation. There is evidence that infants start to imitate novel actions on objects around 6 9 months of age (Barr, Dowden, & Hayne, 1996; Meltzoff, 1988a; Tomasello, 1999). However, it is unclear whether infants acquire the contingencies between observed actions and their effects in the same way as they do for their own actions. If so, infants could learn to predict the effects of observed actions, and they could transfer these effect-expectations to their own actions. The identification with other agents (Meltzoff & Moore, 1994; Tomasello, 1999) would add an important aspect to infantsõ self-knowledge. The present study investigates whether infantsõ action effect exploration behavior changes after observing another personõs actions and their effects, and how the acquisition of observed action effect relations develops in the first and second year of life. 2. Learning about self-performed actions and their effects There is ample evidence that infants are able to learn contingencies between self-performed movements and environmental events that follow these movements (see Rovee-Collier, 1987, for review). This learning ability exists from birth, or it at least develops within the first 2 months of life. For example, 2- to 5-month-olds learn relations between leg kicks and the contingent movements of a mobile (Rovee & Rovee, 1969) or the sounds of a rattle (Rochat & Morgan, 1998), they learn to turn their heads in anticipation of a bottle (Papousek, 1967), and even newborns learn to vary their sucking to hear their motherõs voice (DeCasper & Fifer, 1980). In general, the experience of contingencies between self-performed movements and sensory events is positively arousing for infants (Lewis, Sullivan, & Brooks-Gunn, 1985; Watson, 1972), and Papousek (1969) reported that 4-month-olds are also pleased by a correspondence of the real events and their expectations. Thus, young infants seem to anticipate the contingent effects of their movements, they smile and coo while carrying out the correct response, and they show distress when the expected effects do not occur (Watson, 1972). The main characteristic of this instrumental learning is that the production of the movement is controlled by an interesting event that follows it, but not by a stimulus that precedes it. Hence, the effects of the action determine the infantõs behavior. One important benefit of acquiring action effect knowledge is that it enables the infant to exert control over the environment. If the infant notices that a certain movement is contingently followed by a certain effect, she can try to reproduce the effect by repeating the movement, and infants start to do this by 4 months (Piaget, 1963) or even earlier (Rovee-Collier, 1987). Around 9
3 734 B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) months of age, infants display a new understanding of action effect relations: They start to perform intermediate action steps and to use multiple behavioral means to the same goal. Tomasello (1999) stated that these behaviors indicate a new level of intentional functioning, because infants now differentiate the goal they are pursuing from the behavioral means they use to pursue it. Goal-directed action requires that the infant has a goal in mind ahead of the action and that she represents actions as means to produce the desired effects. Most probably, infantsõ exploration of the contingencies between self-performed movements and their effects helps them to perform goal-directed actions by 9 months. Several researchers conceptualize infantsõ ability to learn about the consequences of actions as a prerequisite for the development of the self (Gergely, 2002; Rochat & Striano, 2000). Neisser (1991) proposes that while performing movements, the infant co-perceives her own body states and the changes in the environment. This co-perception directly specifies the ecological self, that is the knowledge about the self in relation to physical objects. According to Rochat and Striano (2000), self-perception and implicit self-awareness in infancy are the result of intermodal learning. Infants relate the proprioceptive feedback of their movements to sensory information about environmental events. By this, they experience not only that the body is separate from the environment, but also that perceptual consequences may be controlled by own bodily actions. The early understanding of the self as a physical agent whose actions can bring about changes in the environment (Gergely, 2002; Leslie, 1995) may be the basis of the explicit sense of self-awareness, or the conceptual self (Neisser, 1991), which develops in the second year of life. To explain infantsõ ability to learn relations between self-produced actions and their effects, Gergely and Watson (1999) proposed an innate contingency-detection module (CDM) that applies two mechanisms: One is looking forward in time and registers the conditional probability that a movement is followed by a certain stimulus event, and the other is testing backwards, monitoring the relative likelihood that a given stimulus event was preceded by a movement. Thus, infants learn about the consequences of actions by simply monitoring self-performed movements and environmental events that occur in close temporal proximity. As this learning relies on the temporal and probabilistic relations between actions and effects, simple associative learning mechanisms are sufficient to provide the infant with basic knowledge for the ecological self (Neisser, 1991). Learning about actions and their effects helps the infant to produce a desired effect by performing a given movement. Thus, action effect learning can be seen as a prerequisite for goaldirected action. Elsner and Hommel (2001) proposed a two-stage model that explicates the transition from the acquisition of action effect relations to the emergence of intentional action control. Stage 1 of the model resembles Gergely and WatsonÕs (1999) CDM: Self-performed movements and sensory events are coded within the cognitive system, and if a given movement and a given sensory event co-occur repeatedly, their representations are connected by a bi-lateral association (Elsner & Hommel, in press). Accordingly, activating one representation on later occasions will tend to activate the other one, too. Stage 2 of the model deals with how movements are selected to reach desired goals. Intending a goal is claimed to activate the representation of a desired action effect. If this effect representation has been associated to a movement representation, activation will spread, and the movement that had been contingently followed by the desired effect is primed. Thus, actions are selected by anticipating their effects (Hommel, M usseler, Aschersleben, & Prinz, 2001). Although this model was developed to explain empirical evidence
4 B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) obtained in adults, its implications are meant to be valid for the emergence of intentional action control in infants as well. InfantsÕ capacity to learn about the consequences of self-performed movements depends on their action repertoire, and on their postural and motor control (Rochat, 2001). Still, associative learning mechanisms (Elsner & Hommel, 2001, in press) or an innate CDM (Gergely & Watson, 1999) could help infants to detect regularities not only between their own, but also between other personsõ actions and their effects. In this way, infants could gather knowledge about the functionality of actions, like grasping, walking, or turning a handle, before they are able to perform these actions by themselves. Although there has been much research on observational learning in infancy during the last decades, we still not know what exactly infants learn from observing other agents (Want & Harris, 2002) and what they transfer to their own behavior. However, as action effect learning is related to the early development of the self as a physical agent, and observational learning is related to understanding the self as a social agent (Gergely, 2002), combining these aspects could provide important insight in the development of the self in the first 2 years of life. 3. Learning about observed actions and their effects Habituation and preferential-looking studies show that from 6 to 9 months of age, infants detect the regularities between other personsõ actions and their effects, and they are surprised when an agent changes his goal and now thrives for a different effect than before (e.g., Csibra, Gergely, Biro, Koos, & Brockbank, 1999; Woodward, 1998). Further studies revealed that 6- to 9-montholds can understand a movement that looks non-purposeful (like touching an object with the back of the hand; Woodward, 1999) as goal-directed when it is combined with a salient action effect (like pushing the object to a new position; Jovanovic et al., 2003; Kiraly, Jovanovic, Prinz, Aschersleben, & Gergely, in press). Gergely and Csibra (1997) proposed that by 9 months, infants take a teleological stance and interpret other agentsõ actions as goal-directed and rational. However, the perceptual detection of contingencies between observed actions and their effects is one thing, while the transfer to oneõs own behavior may be another. Such transfer would presuppose first that the infant is able to relate the observed action to a self-performed motor pattern, and second that the infant would expect her own actions to produce the same, or at least similar, effects as the modelõs actions. Still, if the infant has explored the effects of own actions, this selfknowledge could help her to infer the goals of other agents from watching their actions, and to transfer observed action effect relations to own behavior. Research on infant imitation shows that although human neonates may mimic some movements of adults (cf. Anisfeld, 1991; Meltzoff & Moore, 1994), observational learning develops not before 6 9 months of age (Barr et al., 1996; Collie & Hayne, 1999; Meltzoff, 1988a; Tomasello, 1999). In general, the range of behaviors that infants imitate expands with age from facial and body movements, to actions on objects (which infants begin to copy at 6 9 months), to intended actions and social goals (Meltzoff, 1995a). Recently, the question of what infants learn form observing others has become an issue of investigation (Huang, Heyes, & Charman, 2002; Provasi, Dubon, & Bloch, 2001; Tomasello, 1999; Want & Harris, 2002). The term observational learning describes that the behavior of an observer is influenced by witnessing a modelõs actions and their consequences. Bandura (1977) claimed that observational and instrumental learning processes do
5 736 B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) not differ, except for the feature that the relations between movements and effects are experienced vicariously in the one and directly in the other. Whereas this definition relates to the behavioristic tradition by highlighting the incentive value of the observed consequences (i.e., has the action been rewarded or punished), recent theories assume that the observer acquires functional knowledge by observational learning (Tomasello, 1999; Want & Harris, 2002). To acquire such know how, the observer has to encode not only the incentive aspects of the modelõs action effects, but has to build up a full representation of both the action and its effects. The pure fact that an infant imitates a modeled action does not allow to tell what she has learned by observation, because the imitation can be the result of different mechanisms (Bellagamba & Tomasello, 1999; Want & Harris, 2002): The infant may have concentrated on the movement and copies it without considering the resulting effect, which is called mimicking. Alternatively, she may have concentrated on the effect and tries to obtain it by any movement from her repertoire, which is called goal emulation. However, imitative learning requires that the infant copies the observed movement and tries to produce the same effect as the model, thus both the movement and the effect must have been encoded. Tomasello (1999) claims that in humans, imitative learning emerges as part of the so-called 9-month revolution. At about 9 12 months of age, infants begin to engage in novel joint-attentional behaviors that involve a referential triangle of child, adult, and object (Carpenter, Nagell, & Tomasello, 1998b) and that indicate an emerging understanding of other persons as intentional agents like the self. According to Neisser (1991), these novel behaviors require a coordinated use of two sources of self-knowledge that develop separately in early infancy: The ecological self described above and the interpersonal self that derives from the perception of contingencies between own actions and those of a partner. Tomasello (1999) proposes that in a social learning situation, the infant has to understand and encode three aspects: First, that the model has the intention to achieve a behavioral goal, second, that he chooses a certain movement for doing so, and third, that if the infant had the same goal she could choose the same action. Thus, imitative learning entails that the infant images herself in the situation of the model, and that she expects her own actions to produce the same effects as the modelõs actions. However, these transferred effect-expectations may not always be met, either because the infant performs the movement in a different way than the model, or because the infant has not encoded specific aspects of the situation that are necessary for the effect to occur (e.g., that pressing a key produces a tone, but only if the electric piano has been switched on). The realization that self-performed actions do or do not lead to the same effects as the modelõs actions provides the infant with important knowledge about the capabilities of the self as an agent among other agents. Around 9 months of age, there seems to be a developmental milestone in infantsõ understanding of actions, which is reflected by the emerging capacities to differentiate goals from behavioral means in self-performed actions, and to acquire means-ends relations, or relations between actions and effects, from observed actions. Another important change emerges around 14 months of age, when infants start to show a more general understanding of other personsõ action goals. At this age, infants distinguish between accidental and intentional actions, and they are more likely to imitate actions that are verbally marked as being intended (Carpenter, Akhtar, & Tomasello, 1998a). Additionally, 14-month-olds imitate novel actions that bring about certain effects in unusual ways, like touching a box with the forehead to make a light appear (Meltzoff, 1988b).
6 B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) However, infants imitate such seemingly irrational actions only if the situational constraints indicate that the model could have performed a more usual action, but has deliberately chosen the unusual action (Gergely, Bekkering, & Kiraly, 2002). Moreover, at months, but not at 12 months, infants infer goals from observed failed attempts, and when imitating these actions, they bring about the effects that the model has failed to achieve (Bellagamba & Tomasello, 1999; Huang et al., 2002; Johnson, Booth, & OÕHearn, 2001; Meltzoff, 1995b). Thus, from the second year of life, children infer the goals of other agents just from watching their actions, and to do this, children most probably refer to their own action effect knowledge, telling them how the action is performed and which effects typically follow it. However, if infantsõ ability to imitate the actions of others relies on their own action effect knowledge, the question is how they could process and reproduce novel actions, or understand novel goals. We will come back to this in the discussion. Although current theories on infant imitation stress the role of action effects or of the goals ascribed to the model, the issues of whether infants learn specific action effect relations by observation and whether they expect their own actions to produce the same effects as the observed actions have not yet been addressed directly. There are some studies, however, that suggest that these aspects play a role in infantsõ imitative learning. For example, Provasi et al. (2001) found that 12-month-olds, but not 9-month-olds, benefit form observing means-ends relations, because they obtained significantly more successes in manipulating a knob to retrieve a toy after having watched a model than after equal amounts of free play. Similarly, Carpenter et al. (1998b) showed that by 12 months of age, infants checked whether their actions would produce effects, like the modelõs actions did, whereas 9 11 months copied the modelõs actions without paying attention to the effects. However, both studies did not vary the effects of the imitated actions, so we do not know whether infants have encoded the specific relations between the observed action and a certain effect. If not so, infants would be satisfied when their own actions are followed by any effect, irrespective of whether this is the same effect that the model has obtained or not. 4. Purpose of the present study Until now, the relations between learning about the effects of self-performed and of observed actions have not been addressed directly in infancy research. Because both instrumental and observational learning provides infants with action effect knowledge, which may be the basis for the production and understanding of goal-directed action, one could speculate that these abilities rely on similar learning mechanisms. However, they seem to follow different developmental courses, with imitative learning emerging later. The reason for this may be that imitative learning not only requires the detection of contingencies between other peopleõs actions and their effects, but two further aspects, namely the transition of the observed action to a self-performed motor pattern and the transfer of the observed action effect relations to oneõs own actions. The purpose of the present study was to investigate (1) the way in which 9-, 12-, 15-, and 18- month-old infants explore an object after the observation of a modelõs actions on that object and their effects and (2) by what age infants expect their own actions to produce the same effects as the modelõs actions. The infants explored a novel object (Fig. 1) that allowed two target actions to be performed (i.e., pressing a plastic ring down or pulling it towards the infant) and two effects to be obtained (i.e., producing a sound or light effect). Three experimental groups differed with respect
7 738 B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) Fig. 1. Overview of the experimental design. Two actions can be performed on the ring (i.e., pressing or pulling) and two effects can be obtained (i.e., producing a sound or lighting up). All infants explored the ring for 120 s (right column). Prior to this, infants in the self-exploration group (Self) saw no demonstration (left column), whereas infants in the two observation groups (Obs) watched an adult performing the two target actions (in 12 demonstration trials) obtaining a certain effect with each action. In the Obs-same group, the infantõs target actions were followed by the same effects as the modelõs actions, while in the Obs-diff group, the action effect mapping for the infant was reversed. to what the infants had seen prior to the exploration phase: In a self-exploration group, the infants explored the object on their own, without a prior demonstration. In two observation groups, the infants watched an adult performing the two target actions on the ring and obtaining a certain effect with each action. The two observation groups differed with regard to the action effect mapping experienced by the model and by the infant: In one group, the infantõs actions were followed by the same effects as the modelõs actions, while in the other group, the infantõs mapping of actions and effects was reversed to that of the model. One reason why research on instrumental and imitative learning has thus far rarely been integrated may be the use of different dependent variables: In instrumental learning, learning curves depict how often the operant action is performed in succeeding time intervals. Imitation research, however, puts the question whether or not target actions are performed by infants in an experimental group who have observed a model, and by infants in a control group who have not. Hence, in imitation research, the question is mainly yes or no, whereas in instrumental learning, the question is how much. As the present study was planned to investigate whether infantsõ exploration behavior would be influenced by the observation of a model, we used the frequency of performed target actions as the dependent variable. If infants learn by observing others, the infants in the two observation groups should be more motivated to act on the ring and thus perform
8 B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) more target actions than the infants in the self-exploration group. The benefits of observational learning should affect the infantsõ behavior directly and should thus be evident at the beginning of the exploration phase. The transfer of effect-expectations should be reflected by a difference in the number of performed actions in the two observation groups: If infants expect their own actions to produce the same effects as the modelõs actions, they should be more motivated to act on the ring when this expectation is met, and thus, the number of performed actions should be higher in the group in which the modelõs and the infantõs action effect mapping correspond. Moreover, cumulated learning curves of the number of performed target actions allow to depict how the potential group differences unfold during the exploration phase. 5. Materials and methods 5.1. Participants The participants were 144 healthy, full-term infants, 36 in each of the four age samples (mean age in months and days: 9;03, 12;00, 15;07, and 18;00, respectively, 9 days). All infants scored within their age range in selected tasks of the Bayley Scales (Bayley, 1993). Fifty-three additional infants were dropped from the study because they did not pull the ring (n ¼ 12), or due to procedural errors (n ¼ 6), malfunctioning of the ring (n ¼ 3), refusal to participate (n ¼ 15), fussiness (n ¼ 13) or parental interference (n ¼ 4) Stimuli and apparatus The test object was a red plastic ring (diameter: 12 cm and height: 3 cm) that was attached horizontally to a wooden stick and placed 5 cm above the table top (Fig. 1). The stick protruded from a white wooden box (length: 30 cm, width: 30 cm, and height: 11.5 cm) and allowed the ring to be pressed down for 2 cm or to be pulled away from the box for 2 cm. When the ring was pressed down or pulled, it produced either a light effect, which consisted in the illumination of small light bulbs hidden inside the ring, or a sound effect, which consisted in the presentation of a c-major triad of MIDI tones via a loudspeaker hidden inside the box. A panel with two switches allowed to vary the mapping of action and effect (i.e., press! light and pull! sound, or press-! sound and pull! light) Design and procedure Each infant was randomly assigned to one of the three experimental groups that consisted of 12 infants in each of the four age samples. All infants went through a similar exploration phase, in which they were allowed to act on the ring for 120 s. Prior to this exploration phase, the infants in a self-exploration (Self) group saw no demonstration and thus assessed the spontaneous exploration behavior on the ring, and the learning of relations between self-produced actions and their effects. The infants in two observation (Obs) groups observed the experimenter pressing and pulling the ring and producing a specific effect with each target action. In the Obs-same group, the infantõs actions in the exploration phase were followed by the same effects as the experimenterõs
9 740 B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) actions, whereas in the Obs-diff group, the mapping of the infantõs actions and effects was reversed to that of the experimenter (see Fig. 1). During the experiment, the parent was seated at a table with the infant on his/her lap, facing the experimenter who sat to the infantõs left. The parent was asked to refrain from speaking and to remain neutral throughout the experiment. When the infant seemed comfortable, the experimenter began with the demonstration in the Obs groups or immediately put the ring into the infants reach in the Self group. During both demonstration and exploration, the ring pointed towards the infant so that the actions and the light effects were completely visible. If the infant became distracted, the experimenter tried to regain the infantõs attention by calling the infantõs name and asking her to look at the ring. However, the experimenter did not use any words that described the actions or effects. The whole session was videotaped for later coding. In the Self group, the infant was allowed to act on the ring for 120 s. The mapping of action and effect was balanced across participants: For half of the infants, pressing of the ring was followed by the sound effect and pulling was followed by the light effect (i.e., action effect mapping A; press! sound and pull! light). The other half of the infants experienced the alternative action effect mapping B (i.e., press! light and pull! sound). In the two Obs groups, the experimenter first kept the ring outside the infantõs reach and demonstrated the two target actions. The whole sequence of 12 demonstration trials consisted of performing 3 target action 1, then 3 target action 2, then again 3 target action 1, and 3 target action 2. For half of the infants, pressing and for the other half, pulling was shown as target action 1. Each target action was followed by an effect, and the mapping of the modelõs actions and effects was balanced across participants: Half of the infants observed the experimenter obtaining action effect mapping A, whereas the other half observed the experimenter obtaining the alternative action effect mapping B. Immediately after the demonstration, the experimenter touched the two-switch panel to change the action effect mapping in the Obs-diff group, or to produce the same noise but leave the action effect mapping unchanged in the Obs-same group. After that, the ring was put inside the infantõs reach and the exploration phase continued as described for the Self group. Thus, all infants were allowed to act on the ring in the same way, but the infants of the Obs groups had previously observed an adult presenting actions and effects, which the infants in the Self group had not. Moreover, an Obs-same infant who experienced action effect mapping A and produced the sound by pressing and the light by pulling the ring had also observed an adult with action effect mapping A, whereas an Obs-diff infant who experienced action effect mapping A had observed an adult with action effect mapping B Scoring The videotapes were scored by a coder who was uninformed of the infantsõ group assignment. The coder recorded how often the infant pressed down or pulled the ring in the 120-s exploration period. To test whether all infants were equally interested in the ring, the latency to the first action and the overall looking time at the ring were also analyzed. A second coder re-scored a randomly selected 25% of the data set. Intercoder agreement was high as evaluated by j (0.94). Analyses were based upon the first coderõs scoring.
10 B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) Results 6.1. Total number of target actions in the 120-s exploration phase To make sure that all infants had explored the two target actions and perceived the two effects, infants who did not pull the ring (n ¼ 12; 1 9 months Obs-same, 1 9 months Self, 2 12 months Obs-same,2 12 months Self,1 15 months Self,2 18 months Obs-same,2 18 months Obs-diff, and 1 18 months Self) were excluded from the analysis and replaced by infants of the same age. All infants performed each target action at least once, and a first analysis of the data revealed that generally infants pressed the ring more often than they pulled it. On average, each infant performed 67.2 target actions, of which were 13.9 pulling and 53.3 pressing actions. Because the ratio of pressing and pulling was about the same in all groups, and the hypotheses referred to the overall frequency of target actions, analyses were conducted on the total number of target actions in the 120-s exploration phase, which was calculated by adding the frequency of pressing and pulling for each infant. Fig. 2 displays the mean number of target actions produced in each of the three experimental groups and four age samples. A 4 3 analysis of variance (ANOVA) with the between-subject factors age and experimental group showed significant main effects of age (F ð3; 132Þ ¼ 18:5; p <:001) and of experimental group (F ð2; 132Þ ¼17:1; p <:001), and a significant age-bygroup interaction (F ð6; 132Þ ¼2:3; p <:05). Paired comparisons yielded that the number of performed target actions increased with age: The 18- and 15-month-olds, which did not differ, performed more target actions than the 12- (p <:001) and 9-month-olds (p <:001), which did also not differ. The main effect of experimental group was due to a higher number of target actions in the Obs-same than in the Obs-diff (p <:005) and the Self condition (p <:001), and to a higher number in the Obs-diff than in the Self condition (p <:01). Fig. 2. Mean number of performed target actions (i.e., pressing and pulling) for the four age samples (9-, 12-, 15-, and 18-month-olds) and the three experimental groups (Self, Obs-same, and Obs-diff) in the 120-s exploration phase. Error bars represent standard errors between participants.
11 742 B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) To investigate the group-by-age interaction, separate ANOVAs were performed within each age sample. These analyses revealed that for the 9-month-olds, the total number of performed target actions did not differ between the experimental groups (F ð2; 33Þ < 1:0). In the 12-, 15-, and 18-month-olds, however, there was a significant main effect of experimental group (12 months: F ð2; 33Þ ¼3:87; p <:05; 15 months: F ð2; 33Þ ¼8:14; p <:005; and 18 months: F ð2; 33Þ ¼ 9:13; p <:005). Planned contrasts indicated that for the 12-month-olds, both the Obs-same (p <:005) and the Obs-diff group (p <:05) performed significantly more actions than the Self group, but that the two observation groups did not differ (p ¼ :24). The differences between the Obs groups and the Self group were also present in the 15- and 18-month-olds (Obs-same vs. Self: p <:001 in both age samples; Obs-diff vs. Self: p <:05 in both age samples). Additionally, the 15- and 18-month-olds in the Obs-same groups produced more target actions than in the Obs-diff groups (p <:05 in both age samples). Hence, from 12 months of age, infants who have observed the model acting on the ring perform more target actions than infants who have not seen the model, and from 15 months of age infants perform more target actions when their own actions are followed by the same effects as the modelõs actions Looking time at the ring and latency to the first action These two measures were about the same in the age samples and experimental groups: Two 4 3 ANOVAs with the between-subject factors age and experimental group yielded no significant main effects or interactions for the latency to the first action (all ps >:13) or for the total looking time at the ring (all ps >:10). Thus, all infants were equally interested in the ring. Nevertheless, the number of target actions they performed was affected by the observation of another personõs actions and their effects Cumulated learning curves To analyze how the group differences in the total frequency of target actions unfold over the 120-s exploration phase, this phase was divided into s intervals, and the total number of performed target actions was calculated for each infant in each interval and cumulated successively over the 12 intervals. Fig. 3 displays the cumulated learning curves for each of the three experimental groups in the four age samples. A ANOVA with the between-subject factors age and experimental group and the within-subject factor block yielded in addition to the already described results for the variables age and experimental group (see section on total number of actions) a significant main effect of block (F ð11; 1452Þ ¼777:4; p <:001), and significant block-by-age (F ð33; 1452Þ ¼15:33; p <:001), block-by-group (F ð22; 1452Þ ¼13:19; p <:001), and age-by-group-by-block interactions (F ð66; 1452Þ ¼2:08; p <:001). So, the differences in the total frequency of target actions emerge in a different way in the age samples and experimental groups. If the group differences between the Obs groups and the Self group would result from observational learning, one would expect the number of performed target actions to differ already in the first 10-s interval. This was confirmed by separate t tests: For the 9-month-olds, the number of target actions performed by the groups in the first block did not differ significantly (all ps >:09). In the 12-, 15-, and 18-month-olds, however, the Obs-same group performed significantly more target
12 B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) Fig. 3. Cumulated learning curves for the four age samples (9-, 12-, 15-, and 18-month-olds), and the three experimental groups (Self, Obs-same, and Obs-diff). The exploration phase was divided into s intervals, and the total number of performed target actions (i.e., pressing and pulling) was calculated for each infant in each interval and cumulated successively over the 12 intervals. actions than the Self group in the first block (12 months: p <:05, 15 months: p <:001; and 18 months: p <:01). This was also the case for the 12- and 15-month-old Obs-diff and Self infants (12 months: p <:005 and 15 months: p <:01), but the 18-month-old Obs-diff infants outperformed the Self infants only from the 5th block (p <:05). The differences between the Obs-same and Obs-diff group in the 15- and 18-month-olds emerge later than between the Obs and the Self groups: In the 15-month-olds, the first significant difference between Obs-same and Obs-diff infants occurs in the 4th block (p <:05), and in the 18-month olds, it occurs in the 10th block (p <:05). Hence, the observation of a model has rather direct impact on the infantsõ behavior, whereas the detection of correspondences between oneõs own and the modelõs action effects takes some time. 7. Discussion The purpose of the present study was to investigate whether 9- to 18-month-old infantsõ individual exploration behavior on an object would change after having observed another personõs actions on that object and their effects, and whether infants would transfer observed action effect relations to their own behavior. The results showed that 12-, 15-, and 18-month-old infants, but
13 744 B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) not 9-month-olds, perform more target actions after having observed the model than when exploring the ring on their own. This replicates and extends previous research and documents that infants benefit from watching other personõs actions and their effects from the beginning of the second year of life. However, the transfer of specific action effect relations to own behavior seems to emerge a bit later. Only from 15 months, infants perform more target actions when their own actions lead to the same effects as the modelõs actions. Thus, although infants learn the contingencies between self-performed actions and their effects from the first months of life (Papousek, 1967; Rochat & Morgan, 1998; Rovee & Rovee, 1969; Watson, 1972), the acquisition of action effect relations by observation emerges not before the second year. This is probably due to the fact that observational learning requires not only the perceptual detection of action effect contingencies, but also the transition of an observed movement into a self-performed action and the transfer of observed action effect relations to own actions. The results of the present study indicate that these capacities develop at different time points around the first birthday Nine-month-olds The exploration behavior of the 9-month-olds was about the same in all groups, irrespective of what the infants had seen prior to the exploration phase. This can be concluded not only from the total number of target actions, but also from the progress of learning as depicted in the cumulated learning curves. Hence, when 9-month-olds get the ring after having observed the model, they explore its functionality as if they had never seen the model. It is important to notice that the lack of group differences is not due to the fact that pressing or pulling implied too high demands on the 9-month-oldsÕ motor capacities. The infants performed about 50 pressing or pulling actions in the 120-s exploration phase, so their motor performance is comparable to that of the 12-month-olds in the Self group, who explored the ring on their own. Instead, the absence of group differences in the 9-month-olds can most probably be attributed to a lack of observational learning in the two Obs groups. Given TomaselloÕs (1999) considerations on the 9-month revolution and the general evidence that infants start to imitate novel actions on objects by 6 9 months of age (e.g., Barr et al., 1996; Meltzoff, 1988a), these results seem surprising. However, the evidence for imitation in this age is restricted on simple actions with novel objects. So, for example, Meltzoff (1988a) showed that 9- month-olds perform more target actions (like shaking a plastic egg) after having seen a model performing these actions, than after having seen the model merely touching the objects, performing alternative actions, or after no demonstration. Similar results were obtained with infants from 6 to 9 months by Heimann and Meltzoff (1996), Barr et al. (1996), Collie and Hayne (1999), and Carver and Bauer (1999). All of theses studies comprised novel combinations of simple actions and unfamiliar objects like pulling a handle, shaking a mitten, or pressing a button. Additionally, all of these studies asked yes-or-no questions by comparing whether more infants who had observed a model would perform the target actions than infants who had seen different manipulations or nothing at all. Thus, these studies show that 6- to 9-month-olds are able to copy novel actions on objects and that the target actions were actually novel because the infants in the control groups did not invent them by themselves (Elsner, in press; Meltzoff, 1988b). In contrast, studies on imitative learning (Carpenter et al., 1998b; Provasi et al., 2001) showed that 9-month-olds did not learn means-end-relations by observation. Hence, younger infantsõ
14 capacity to imitate novel actions on objects may not be the result of imitative learning, but rather of mimicking (cf. Want & Harris, 2002, for a similar conclusion): Although 9-month-olds copy the actions of a model, they seem to be oblivious to the effects of those actions. The results of the present study confirm these findings. Apparently, the actions of pressing and pulling were not novel for the 9-month-olds, because the infants in the Self group, who have not observed the model, were equally likely to perform the target actions as the infants in the Obs groups. The novel information that could have been learned was that the target actions are means to bring about interesting light or sound effects. The results indicate that 9-month-olds either do not detect the functional relations between target actions and effects in the modelõs behavior, or that they do not transfer the observed action effect relations to their own behavior. Still, the demonstration of two actions and two effects may have made the task too difficult for the infants. Habituation studies demonstrate that 9-month-olds and even younger infants are very well able to visually detect regularities between actions and their effects (Csibra et al., 1999; Jovanovic et al., submitted; Kiraly et al., in press; Woodward, 1998, 1999). Therefore, 9-month-olds seem to have difficulties in transferring the observed action effect information to self-performed actions. Yet, further studies that use simpler demonstration conditions are needed to clarify this issue. One could speculate that at 9 months, infants still rely on the ecological self (Neisser, 1991), or the self as physical agent (Gergely, 2002), and thus, they have to perform actions by themselves in order to explore their consequences (i.e., their cognitive functioning reflects Stage 1 in the model of Elsner & Hommel (2001)). When observing other agents, they learn about novel movement patterns, and they are able to transfer these patterns into self-performed actions. Thus, the first prerequisite of observational learning, the transition of visually perceived actions to motor patterns, is present at 9 months, and it enables the infant to mimic the action. However, 9-month-olds seem to disregard the effects of the observed actions, or they seem not to transfer the observed action effect-relations to their own actions Twelve-month-olds B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) By the age of 12 months, infants benefit from observing the model. This is not only evident from the total number of target actions (i.e., Obs infants perform more target actions than Self infants) but also from the learning curves (i.e., the difference between the Obs groups and the Self group is present from the beginning of the exploration phase). After observing the model who performs the target actions and produces interesting light or sound effects, the infants perform more target actions than when exploring the ring on their own. However, the behavior of the two Obs groups does not differ significantly in the 12-month-olds. Thus, infants benefit from observing other personsõ actions and their effects, but the fact that their own action effect mapping does or does not correspond to the observed mapping has no strong impact on their exploration behavior. The lack of performance differences between the two Obs groups makes it difficult to decide whether the infants have learned action effect relations at all, or whether they were just mimicking the target actions (Tomasello, 1999; Want & Harris, 2002). However, other studies have shown that 12-month-olds do learn means-ends relations by observation. For example, Hauf, Elsner, and Aschersleben (in press) demonstrated that infants of this age are more likely to imitate the step of an action sequence that is followed by a salient action effect. Thus, they must have learned which
15 746 B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) of the observed action steps had produced the effect. Carpenter et al. (1998a) delayed the effect of the infantõs action (i.e., a bulb lighting up) and checked whether infants would look at the location where the effect of the modelõs action had appeared. Nine- and 12-month-olds copied the target actions, but only the latter checked whether their actions would bring about an effect. Thus, 12- month-olds have encoded that the modelõs actions had produced an effect, and they expected their own actions to be effective, too. However, because the infants always obtained the same effect as the model, we do not know whether they would be surprised by obtaining a different effect, say a tone instead of the light. The same is true for the study of Provasi et al. (2001), in which 12-montholds, but not 9-month-olds, benefited from observing a model when manipulating a knob to retrieve a toy. Thus, although there is evidence that by 12 months, infants learn action effect relations by observation, in the present study infants at this age did not alter their exploration behavior when their own action effect mapping was reversed to that of the model. This implies that they did not encode the specific relations between observed actions and their effects. If 12-month-olds do not encode specific action effect relations, their behavior could either result from goal emulation or from blind imitation (Tomasello, 1999; Want & Harris, 2002): In goal emulation, the observer learns by observation that a particular goal can be achieved and sets about achieving the goal by his own behavioral means. As the ring did not allow too many actions to be performed, infants who would have ignored the target actions but concentrated on the light and sound effects would most likely discover the target actions by themselves, just like the infants in the Self group do. However, several studies (Bellagamba & Tomasello, 1999; Elsner & Aschersleben, 2003; Provasi et al., 2001) failed to find goal emulation in 12-month-olds. These studies comprised an emulation condition, in which the model presented only the effects, but not the target actions that produce them. Twelve-month-olds in such a condition performed less target actions than in a full demonstration condition. Hence, they apparently need to see both the actions and the effects to be able to reproduce the target actions. This was further supported by Bellagamba and Tomasello (1999) with a group who observed an adult demonstrating arbitrary actions that did not result in any salient effects, and in the study by Hauf et al. (in press) in which only one of two action steps produced a salient effect. In both studies, 12-month-olds did not imitate many of the effect-less actions, and thus, one can conclude that infants at this age need to observe both the action and its effects to see the action as something worth imitating. The fact that 12-month-olds need to see both the actions and the effects speaks against the assumption that their behavior results from goal emulation. Instead, it might be better described as blind imitation (Want & Harris, 2002): Here, the observer replicates both the form and the goal of an observed behavior, but fails to understand the link between the target action and the effects. The cumulated learning curves of the present study provide evidence for blind imitation. If the infantsõ behavior would result from goal emulation, all groups should perform an equal amount of target actions in the first 10-s interval, because all infants would have to discover the action possibilities of the ring by trial and error. However, the Obs infants perform more target actions than the Self infants already in the first 10-s interval. Hence, they have learned by observation not only about the effects that could be obtained, but also about the target actions that could be performed. But they seemingly paid no attention to exactly which action produced which effect. Taken together, there is evidence that 12-month-olds learn relations between observed actions and their effects by observation, but only when they see both the action and the effect. This implies that they are still in the phase of gathering knowledge about actions and their effects (i.e., Stage 1
16 in the model of Elsner & Hommel, 2001). Yet, they are already able to learn not only from their own actions, but also from observing others. Moreover, observing others is more motivating for the infants. Hence, 12-month-olds are able to translate observed actions into self-performed actions and they expect their own actions to be as effective as the modelõs actions. However, their imitation is still blind (Want & Harris, 2002), because they do not yet understand the specific relations between the observed actions and their effects Fifteen- and 18-month-olds B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) From 15 months on, infants not only perform more target actions after having seen the model, but are especially motivated to perform the target actions when their own actions lead to the same effects as the modelõs actions. This indicates that 15- and 18-month-olds encode the specific relations between the observed actions and their effects. The cumulated learning curves demonstrate that the infants need some time to detect whether the effects of their own actions do or do not correspond to the effects of the modelõs actions: For the 15-month-olds, the Obs-same group starts to perform more target actions than the Obs-diff group after 30 s. Somewhat surprisingly, this interval is longer for the 18-month-olds, where the difference emerges only after 90 s. This may be due to the fact that the detection of the mismatch between the infantõs and the modelõs action effect mapping may affect behavior in different ways: Younger infants may be more motivated when they obtain the same effects as the adult, but older infants may be more motivated to explore the box in order to find out what is wrong when their own actions lead to different effects than the modelõs actions. However, the older Obs-diff infants seem to loose interest in this exploration after 90 s, and this may be the reason for the overall group difference. Still, the different overall number of performed target actions in the Obs-same and the Obs-diff groups indicates that 15- and 18-month-olds learn specific action effect relations by observation. The capacity to learn specific action effect relations by observation might be the prerequisite for a new class of imitation behaviors that emerge around 14 months, like the imitation of novel and seemingly irrational actions (like touching a box with the head to produce a light; Meltzoff, 1988b). To reproduce this target action, the infant has to encode both the specific action and the effect that it leads to. Gergely et al. (2002) demonstrated that 14-month-olds also encode situational constraints that may force the model to choose a certain action. The infants imitated the head-on-box action only when the modelõs hands were free during demonstration. However, when the modelõs hands were occupied, most of the infants used their hands (which were not occupied like the modelõs) to touch the box and make the light appear, which is a more rational action in the sense of Gergely and Csibra (1997). Thus, by 14 months, infants encode the observed action, its effects, and the situational constraints, and they are able to decide whether they imitate the model or whether they choose a more rational action from their repertoire to obtain the same effect. Fourteen-month-oldsÕ readiness to imitate an action is not only dependent on situational constraints, but also on verbal cues indicating whether the demonstrated action was intended or occurred by accident. In a study by Carpenter et al. (1998a), 14- to 18-month-olds were more likely to imitate actions when the model said There! while performing them than when the model said Whoops!. Thus, the infants did not automatically reproduce actions they had seen, but their emerging ability to understand verbal cues helped them to decide which action should be
17 748 B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) imitated. The fact that 14-month-olds are able to decide whether they imitate an action or not indicates that at this age, infants are able to use their action effect knowledge in a flexible way. Moreover, if the infant touches the box with the hand in Gergely et al.õs (2002) study, she has to be able to operate on broad action effect knowledge in order to find an alternative action that is suitable to obtain the observed effect. Thus, infantsõ behavior at 14 months indicates that Stage 2 of Elsner and HommelÕs (2001) model has emerged, and that infants are able to activate acquired action effect representations bi-directionally. This enables them to predict the typical effect of a self-performed or observed action, and also to find an action that is suitable to produce a desired effect. Most probably, the flexible use of action effect knowledge also enables 15- to 18-month-olds to infer action goals from observed failed attempts. Meltzoff (1995b), Bellagamba and Tomasello (1999), Johnson et al. (2001), and Huang et al. (2002) showed that 15- to 19-month-olds who observed a model trying, but failing to achieve the end result of a target action (e.g., to pull apart a dumbbell), produced about as many target actions as infants who observed a successful demonstration. This re-enactment of failed attempts has been interpreted as evidence that the infants can infer the modelõs intentions, which enables them to produce the intended instead of the observed effect. However, Huang et al. (2002) demonstrated that re-enactment could as well result from non-imitative learning processes that do not involve the infantõs ascription of intentions to the adult. Similarly, the action effect learning perspective proposed here would not require that the infant reads the modelõs intentions in a mentalistic fashion. All the infant would have to do is encode the observed action and retrieve its typical effect from her action effect knowledge. Under this perspective, younger infantsõ disability to re-enact failed attempts (Bellagamba & Tomasello, 1999) may have two reasons: They either have not yet acquired the necessary action effect knowledge, or they fail to relate the observed action to their knowledge. If infantsõ imitation is based on their action effect knowledge, the question is how they could imitate novel actions or novel goals. To many researchers, imitation of novel behaviors is a milestone in cognitive development (Meltzoff, 1988b; Piaget, 1963), but the problem is how to define novelty. According to Meltzoff (1988b), an act can be novel in six senses: It has never been (a) seen, (b) performed, or (c) imitated by the infant before; (d) it is not a well-practiced game; (e) it has not been performed with a particular object before; and (f) it occurs with near-zero probability in spontaneous play. The evidence for infant imitation obtained so far mostly fulfills criteria (d) (f). Most studies demonstrate a novel combination of an action that is familiar to the infant (e.g., shaking, pulling, and touching) with an object that may or may not be familiar (e.g., a toy or a self-built apparatus) to produce an interesting effect that is mostly not familiar in this special setting. So the novel part is the combination of more or less familiar components, which is reflected in criteria (d) (f). The problem with MeltzoffÕs criteria (a) (c) is how individuals could at all imitate behaviors that are not in their repertoire (Elsner, in press). This becomes especially obvious in infant imitation: A 9-month-old who has difficulty in releasing a small object from her hand will not imitate putting a ball in a cup (Elsner & Aschersleben, 2003). Similarly, older infants in most cases do not copy the actions of the adult model in all their kinematic aspects, but perform an approximation of the observed behavior. For example, in the present study, while the model used a flat hand to press the ring down (Fig. 1), most infants closed the fingers of one or both hands around the ring. This could indicate that infants have to rely on motor patterns in their repertoire when
18 B. Elsner, G. Aschersleben / Consciousness and Cognition 12 (2003) transferring the observed actions to self-performed movements, and the copy of the action would be as good as the fit of the infantõs and adultõs motor pattern. However, this does not mean that infants cannot imitate actions they have never performed before. If the novel action comprises a combination of familiar action steps, or if it can be approximated by an action in the infantsõ repertoire, the infant may well be able to imitate. Besides helping the observer to anticipate the typical effects of self-performed or observed actions, the flexible use of action effect knowledge is also a prerequisite for goal emulation, in which the observer chooses an action of his repertoire to produce an observed effect. Taken this way, it is astonishing that 18-month-olds do not produce target actions after having seen only the end result (Bellagamba & Tomasello, 1999). However, Huang et al. (2002) showed 17- and 19-month-olds both the initial state of the object and the end result in an emulation condition, and in this condition, infants showed emulation and performed about the same proportion of target actions as the infants in the full demonstration condition who had observed the target action. Moreover, studies that have recorded other behaviors than only the target actions provide additional evidence for goal emulation in 14- to 19-month-infants: Gergely et al. (2002) reported that all infants who imitated the head-on-box action also touched the box with their hands, and they explain this behavior by an automatic process by which remembering the effect (i.e., illumination by touch) activates the response that is most strongly associated with producing this effect (i.e., hand action). Similarly, Huang et al. (2002) report that some infants try to activate a buzzer hidden in a box not with a stick (which would have been the target action), but with their finger (which is the typical way to activate a switch). In conclusion, by 14 months, infants may be able to emulate actions when they see the initial state and the end result, but only when the observed action can be substituted by an action for which the infant has acquired sufficient action effect knowledge. Taken together, although infants learn about the effects of self-performed actions from the first months of life, and although they are able to perceptually detect relations between other personsõ actions and their effects from the middle of the first year, the transfer of observed action effect relations to own behavior seems to emerge not before the first birthday. However, by about 14 months of age, infants seem to have acquired broad action effect knowledge that may be the basis for their capability to infer the effects of observed actions and to infer the actions that may have led to observed effects. Thus, learning about the effects of self-performed and observed actions equips the infant with knowledge that supports both the production and the understanding of goal-directed action. Acknowledgments Parts of these findings were reported at the International Conference on Infant Studies (ICIS) in Toronto, Canada, in April 2002, and at the EURESCO Conference Brain Development and Cognition in Acquafredda di Maratea, Italy, in June Much appreciation to the infants and parents who participated in this research. We thank Malinda Carpenter and G unther Knoblich for their helpful comments. Thanks also to Maria Zumbeel for making the appointments, Inga Gegner, and to the student research assistants for running the experiments and scoring the video tapes, and to Fiorello Banci and Karl-Heinz Honsberg for constructing the apparatus.
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