Infants' attentional preference for object-related

Infant Behavior & Development 35 (2012) 533–542

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Infant Behavior and Development

Infants’ attentional preference for object-related actions of older children compared to object-related actions of peers and adults Norbert Zmyj a,∗ , Moritz M. Daum b , Wolfgang Prinz b , Gisa Aschersleben c a b c

Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany Saarland University, Saarbrücken, Germany

a r t i c l e

i n f o

Article history: Received 12 March 2009 Received in revised form 24 January 2012 Accepted 16 March 2012 Keywords: Infants Children Attention Preference Heart rate

a b s t r a c t Previous research reports mixed results concerning infants’ differential interest for a specific age group. Most of these findings are based on studies using static photographs and drawings as stimuli. Moreover, only behavioral data were used to investigate infants’ attentional preferences. In the present study, we showed video sequences of differently aged models (peers, 3.5-year-olds, and adults) manipulating an object, and measured heart rate as an objective psychophysiological measurement of infants’ attention, in addition to looking time and banging rate. The results showed that 12-month-olds preferred watching older children’s object-related actions compared to those of peers and adults, but 6- and 9-month-olds did not. In subsequent control experiments, alternative explanations that this preference relied merely on the visual appearance or a higher activity level of older children were excluded. We explain this observed developmental shift by the increasing importance of social learning and object use at this age. Thus, 12-month-olds prefer watching more knowledgeable individuals who provide an action repertoire that infants of this age are about to develop. © 2012 Elsevier Inc. All rights reserved.

1. Introduction From early on, infants encounter individuals of various ages in the family or at day care centers. Before any dyadic interaction with another individual can take place, infants have to attend to the other individual’s behavior. This observed behavior can be of different complexity and familiarity depending on, for example, the other’s age. The age of an observed person may therefore be an important cue for infants to guide their attention. It is, therefore, important to learn more about infants’ interest in individuals of different ages. The aim of the present study is to investigate infants’ perception and attentional reaction during the observation of differently aged others. The different age groups infants encounter in their first year of life can roughly be categorized as follows: same aged peers, older children, and adults. Each of these groups might attract infants’ attention for different reasons and each of these attentional preferences may provide a specific benefit. Supporting evidence for each of these preferences can be found in the infancy literature and is summarized below. In this literature review, we focus on studies that were designed to investigate infants’ attentional preference and the results are somewhat contradictory. However, in the studies reported, attentional preference was measured using different methodologies. Accordingly, it is difficult to evaluate whether seemingly contradictory findings were merely based on a difference in methodology.

∗ Corresponding author. Tel.: +49 234 3227783. E-mail address: [email protected] (N. Zmyj). 0163-6383/$ – see front matter © 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.infbeh.2012.03.003

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N. Zmyj et al. / Infant Behavior & Development 35 (2012) 533–542

1.1. Preference for same-aged peers There may be two reasons why infants might exhibit an attentional preference for their peers. First, as Sanefuji, Ohgami, and Hashiya (2006) pointed out, infants have babyish characteristics and are most similar in appearance to infants. Lorenz (1942) reported that the babyish characteristics, such as relatively big eyes, forehead arch, and chubby cheeks elicit caretaking behavior across different species. It has been suggested that the positive affect elicited by viewing babyish characteristics is already present in infancy (Lorenz, 1942; McCall & Kennedy, 1980). Thus, the mere appearance of an infant makes its observation more interesting than the observation of older children or adults. Second, Piaget (1962) suggested that peers are important for a child’s cognitive development, because they share a similar worldview. In line with this, Meltzoff (2005) suggested that infants perceive others as being “like me”. That is, infants understand others based on their understanding of the own behavior. In terms of the motor repertoire and cognitive abilities, peers are the most similar others to the infant among individuals of various ages. Based on the idea that infants have an attentional preference for individuals whose behavior is easier to make sense of, peers might attract infants’ attention more than older children or adults do. Research on the mirror neuron system in adults supports this idea, as this system is thought to respond to observed familiar and executable actions that are ‘like me’ (Rizzolatti & Craighero, 2004). Evidence for infants’ attentional preference for observing peers comes from McCall and Kennedy (1980). They reported that the time 4-month-olds spend looking at facial drawings of differently aged individuals increased with the decreasing age of the person depicted. Subsequently, controversial findings were reported by Sanefuji, Ohgami, and Hashiya (2005). In their study, 8-month-olds banged their arms more frequently during the observation of adults and infants than during the observation of older children. However, it is disputed whether this motor activity denotes attentional preference (Sanefuji et al., 2005), frustration (Behne, Carpenter, Call, & Tomasello, 2005), or self-induced vestibular stimulation (Thelen, 1980). Since multiple reasons could be responsible for the infants’ banging, this finding is inconclusive. 1.2. Preference for older children Vygotsky (1978) highlighted the importance of knowledgeable others for a child’s development. He speculated about a zone of proximal development, which is created by others when providing knowledge to young children. This zone of proximal development is defined as “the distance between the actual developmental level as determined by independent problem solving and the level of potential development as determined through problem solving under adult guidance or in collaboration with more capable peers” (Vygotsky, 1978, p. 86). According to Vygotsky, it is necessary for the establishment of the zone of proximal development that it does not ask too much of the infant. Older children meet this criterion by default. Therefore, infants might exhibit an attentional preference for older children. Preference for older children received support by empirical findings showing that 7-month-olds preferred looking at video sequences of children’s faces (9 years of age) compared to adults’ faces (25–30 years of age, Bahrick, Netto, & Hernandez-Reif, 1998). Furthermore, in family day care centers, 16–23-month-olds spent more time looking at toddlers in the third year of life than at same-aged toddlers (Rothstein-Fisch & Howes, 1988). 1.3. Preference for adults Finally, there are also reasons for infants to preferably watch adults. Csibra and Gergely (2006) put forward the idea of a natural pedagogy that adapts infants to quickly learn culturally relevant behavior. That is, on the one hand, adults naturally tend to mark their relevant behavior with ostensive cues (e.g., motherese, lifting eyebrows, addressing the infant by name) when they interact with infants. On the other hand, infants are naturally prepared to correctly interpret ostensive and referential cues in order to learn the corresponding behavior. By default, adults are more knowledgeable and experienced in cultural artifacts than children or peers. Accordingly, infants might have a bias towards tracking an adult’s action compared to the actions of peers or older children. So far, there is only indirect evidence for an attentional preference for adults coming from recent imitation studies with differently aged models. In these studies, infants imitated novel actions performed by adults more often than novel actions performed by peers (Seehagen & Herbert, 2011; Zmyj, Daum, Prinz, Nielsen, & Aschersleben, in press). However, despite these studies, we still do not know whether a preference for imitating the adult is caused by a preference for attending to adult models or by other processes that are involved in imitation, such as an evaluation of the model’s relevance. Previous research on infants’ attentional preference is limited by two factors. First, all the studies reported that investigated infants’ attentional preference, when viewing different aged individuals, have used only behavioral methods, such as looking time and banging rate. In order to extend and clarify infants’ perception of different age groups, we used heart rate as an objective psychophysiological measure in the present study, in addition to looking time and banging rate. Heart rate deceleration and a lower mean heart rate is usually associated with an increase in attention (Campos, Emde, Gaensbauer, & Henderson, 1975; Elsner, Pauen, & Jeschonek, 2006; Lansink, Mintz, & Richards, 2000). Heart rate deceleration is attributed to the orienting response, beginning with an initial deceleration in heart rate at stimulus onset and a subsequent phase of sustained lowered heart rate accompanying sustained attention. Finally, when attention ceases, heart rate returns to the pre-stimulus level (Richards, 1997).


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Second, most of the previous studies investigating infants’ attentional preference when viewing differently aged individuals used static stimuli (for exceptions, see Sanefuji et al., 2005, 2006). However, infants are highly interested in actions. For example, infants attend to actions more than faces (Bahrick, Gogate, & Ruiz, 2002). As a consequence, previous studies using drawings or photographs to demonstrate an attentional preference cover only one aspect of perception of others. Little is known on how infants perceive the actions of differently aged models. Therefore, we presented infants with videos showing differently aged models to make the stimulus presentation more life-like compared to a presentation of static stimuli. Accordingly, the present study was designed to explore the attentional preference of infants in their first year of life, when presented with differently aged models acting with an object. In Experiment 1, 6-, 9-, and 12-month-old infants’ attentional reactions to video sequences of differently aged models were analyzed using the measurement of heart rate, looking time, and banging rate. Experiments 2, 3a, and 3b were designed to more closely investigate the nature of the attentional preference effect found in Experiment 1. In Experiment 2, we investigated the impact of facial features by showing only the hands and the upper body of the actor, but not the face. In Experiment 3a, we showed still images of the three age groups, in order to test whether it is the mere visual appearance of the models that elicits an attentional preference. In Experiment 3b, we examined the role of the overall activity of the individuals presented in the video sequences by showing distorted versions of the video sequences. 2. Experiment 1 We tested 6-, 9-, and 12-month-old infants’ attentional preference when watching video sequences of differently aged models displayed on a monitor. Each infant was presented with six different models (two of each model age group) acting on an object. During the 2 min of presentation, we measured looking time, heart rate, and banging rate. 2.1. Method 2.1.1. Participants Eighty-one infants participated in this experiment: Twenty-seven 6-month-olds (13 girls, 14 boys; M = 6 months 6 days, range = 5;20–6;15), twenty-five 9-month-olds (16 girls, 9 boys; M = 9;02, range = 8;18–9;13) and twenty-seven 12-montholds (13 girls, 14 boys; M = 12;07, range = 11;21–12;15). Twenty-eight additional infants were not included in the final sample due to: equipment failure (6-month-olds: n = 1; 9-month-olds: n = 11; 12-month-olds: n = 3), fussiness (6-month-olds: n = 1; 9-month-olds: n = 5; 12-month-olds: n = 6), or interference by the parent (12-month-olds: n = 1). Infants were recruited from a database of parents who had agreed to participate in infant studies. Thirty-one infants had older siblings (6-month-olds: n = 12; 9-month-olds: n = 8, 12-month-olds: n = 11) under the age of 18 with none of them being twins. One sibling was 26 years old and was not considered an older sibling. 2.1.2. Stimuli The stimulus material consisted of video recordings of twelve infants (four 6-, 9-, and 12-month-olds, respectively), four 3.5-year-olds, and four adults. Each model age group consisted of two male and two female models. During the recording session, all models wore identical blue t-shirts and sat at a table in front of white background. They played freely with one of two objects (yellow rubber duck or multi-colored soft cube). The action consisted of simple object manipulations (e.g., squeezing the soft cube, sliding the rubber duck on the table). Although the actions were similar across the different age groups there were small differences in the velocity, range or intensity of movements. From these recording sessions, eight 10-s video sequences (4 models × 2 toys) without sound were prepared for each model age group. 2.1.3. Test environment, apparatus and measurement Infants were tested in an unfurnished laboratory that only contained a table, a monitor and white curtains. The actions performed by the differently aged models were presented via the software presentation® (Neurobehavioral Systems, Inc., Albany, CA, USA) on a 24-in. monitor (SONY GDM-FW900, screen resolution 800 × 600). During the entire experiment, the infants sat on their parent’s lap at a table (80 cm × 60 cm), which was located between the monitor and the infant. The distance between the infant and the monitor was approximately 70 cm. A camera was positioned above the monitor and recorded a close-up view of the infant during the presentation of the video sequences. A second camera was focused on the monitor to record the video sequences shown. Both camera views were recorded together using a split screen generator. The heart rate of the infant was assessed by three Ag–AgCl electrodes placed on the infant’s chest. The electrocardiogram was sampled at 200 Hz and digitized by a data acquisition interface (MP35, BioPac Inc., Santa Barbara, CA, USA). The R-wave was identified in the electrocardiogram, and the interbeat interval was defined as the duration between successive R-waves. Additionally, the computer software transformed the interbeat interval in the heart rate to beats per minute (bpm) on-line. The experimenter sat in an adjacent room, watched the close-up view of the participating infant and coded looking time on-line by pressing a button that was connected to the computer running the electrocardiogram software. The experimenter held down the button as long as infants looked to the monitor und she released the button when infants looked away. The two computers running the software for the presentation of the stimulus material and for the recording of the electrocardiogram were linked in order to indicate onset and offset of each video sequence within the heart rate data. This parallel recording of stimulus onset, looking behavior and heart rate allowed the computation of mean heart rate while the infant watched

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Table 1 Mean looking time, mean heart rate, mean number of bangs and parental reports of preferred age group for 6-, 9-, and 12-month-olds in Experiment 1. Standard deviations are given in parentheses. Model age group 6-month-olds Peers Older children Adults 9-month-olds Peers Older children Adults 12-month-olds Peers Older children Adults

Mean heart rate (bpm)

Mean looking time (percentage)

Mean number of bangs

Parental report (percentage)

135.6 (11.2) 135.0 (11.3) 135.5 (11.4)

76.7 (14.5) 81.8 (13.0) 81.3 (14.0)

2.4 (2.5) 2.4 (2.4) 2.2 (2.4)

46 58 8

130.1 (10.3) 129.6 (10.0) 129.8 (9.5)

81.1 (12.6) 79.9 (12.2) 81.6 (10.0)

2.5 (1.8) 2.2 (2.1) 2.4 (2.3)

41 44 19

123.0 (10.2) 121.1 (9.9) 123.3 (9.9)

79.8 (13.5) 86.8 (7.8) 85.6 (13.3)

2.4 (3.4) 2.1 (3.5) 1.9 (3.0)

22 70 11

the video. Additionally, a research assistant used the video recording in order to code the frequency of banging arms offline while the participant looked at the stimulus. Banging arms was defined as fast vertical upwards movement of at least one arm that was followed by a fast vertical downward moment (or vice versa). A second independent observer recoded 25% of the infants using the video recording. Good levels of inter-rater reliability were obtained for looking time (r = .88, Intraclass correlation) and banging (r = .80, Intraclass correlation). To assess infants’ preferred age group, parents received a questionnaire after testing, including the question “Which age group does your child prefer in everyday life?” The parent was given the choice between the categories “adults”, “older children”, “peers” and “none of the above”. Multiple answers were possible. 2.1.4. Procedure Each participant and their parent were first escorted to a reception room. For approximately 10 min, the infant was allowed to explore the room while the research assistant described the test procedure to the parent. The research assistant then placed the electrocardiogram electrodes on the infant’s chest and the infant and parent were brought to the testing room. Infants were individually tested in the laboratory with one parent present. Infants were seated on their parent’s lap in front of the computer monitor. The research assistant then left the room and started the computer-controlled presentation of the stimulus material from an adjacent room. An audio-visual attention getter preceded each presentation of a new model. Each video sequence was presented twice in succession. Infants viewed 6 models (2 of each model age group) in a randomized order playing with either the duck or the cube. It should be noted that each infant was presented with a set of videos that included only one toy and that the differently aged participants (6-, 9-, and 12-month-olds) were presented only with peer models of their age group and not with infant models of the remaining age groups. 2.2. Results 2.2.1. Heart rate To analyze the infants’ mean heart rate data, we conducted a mixed design analysis of variance (ANOVA) with repeated measures, with model age as within-subjects variable (peer models, older child models, and adult models) and participant age as between-subjects variable (6-, 9-, and 12-month-olds). There was a main effect of model’s age, F(2, 75) = 3.31, p < .05, and no interaction between participant age and model age, F(4, 73) = 1.08, p = .37. In order to explore the possibility of a developmental trend, we then calculated the mean heart rate measured in bpm for the periods when the infants looked at the screen (see Table 1). An ANOVA with repeated measures revealed no reliable effect of model age group for the 6- and 9-month-olds, F(2, 24) = .46; p = .63, F(2, 22) = .27; p = .76, respectively. However, 12-month-olds differentiated between the model age groups, F(2, 24) = 3.74; p < .05. Separate t-tests revealed that 12-month olds’ heart rates tended to be lower while observing older children than while observing peers, t(26) = 2.04, p = .052 and was significantly lower than when viewing adults, t(26) = 2.80, p < .05. The difference in heart rate between peers and adults was not significant, t(26) = .26, p = .80. 2.2.2. Looking time We analyzed infants’ mean looking time by conducting a mixed design ANOVA with repeated measures, with model age as within-subjects variable (peer models, older child models, and adult models), and participant age as between-subjects variable (6-, 9-, and 12-month-olds). There was a main effect of model age, F(2, 75) = 3.59, p < .05 and no interaction between participant age and model age, F(4, 73) = 1.29, p = .29. In order to explore the possibility of a developmental trend, we compared percentages of looking time toward the three model age groups within each participant age group separately (see Table 1). An ANOVA with repeated measures for the 6- and 9-month-olds indicated no effect of model age group, F(2, 24) = 1.98; p = .16, F(2, 22) = .55; p = .41, respectively. In contrast, the group of 12-month-olds differentiated between the three model age groups: An ANOVA conducted on the looking times yielded a main effect of the model’s age, F(2, 24) = 3.47; p < .05. Separate t-tests showed that 12-month-olds looked longer at the video sequences of older children than at video


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sequences of peers, t(26) = 2.76; p < .05. Likewise, 12-month-olds tended to look longer at the video sequences of adults than at video sequences of peers, t(26) = 1.73; p = .10, and looking times did not differ between older children and adults, t(26) = .46; p = .64.

2.2.3. Banging We analyzed the mean number of bangs in response to the different aged models in the three participant age groups (for means, see Table 1). ANOVAs for each participant age group revealed no significant effects of model age group (all Fs < 1).

2.2.4. Parental report We asked parents which age group their infant preferred in everyday life (see Table 1). Friedman’s two-way analysis of variance revealed that 6-month-olds differed in their preference for different age groups, 2 (1, N = 26) = 13.9; p < .01. Separate Sign tests indicated that parents perceived their infants as preferring peers and older children compared to adults (p < .01, and p < .001, respectively) but they were not perceived as differentiating between older children and peers. In contrast, the parents of 9-month-olds did not report any significant differences in the preferential behavior, 2 (1, N = 25) = 5.06; p = .08, Friedman’s test. However, a Friedman’s two-way ANOVA revealed that there are differences in the preferences of 12-montholds (2 (1, N = 27) = 19.73; p < .001). Separate Sign tests indicated that they the infants were reported to prefer older children over peers and adults (p < .01 and p < .001, respectively), whereas they did not prefer peers over adults or vice versa (p = .45).

2.2.5. Influence of having an older sibling We analyzed whether having an older sibling had an impact on the heart rate, looking time, or banging rate. A mixed design analysis of variance (ANOVA) with repeated measures, with model age as a within-subjects variable (peer models, older child models, and adult models) and presence of an older sibling as a covariate (sibling vs. no sibling) revealed no main effect of the presence of an older sibling and no interaction between the presence of an older sibling and model age for all three dependent measures (all ps > .25).

2.3. Discussion In sum, Experiment 1 revealed that infants preferably observe object-related actions of older children in comparison to the object-related actions of peers and adults, as indicated by looking time and heart rate. Separate analyses for each participant age group revealed that this effect is mainly driven by the data of the 12-month-olds. Accordingly, while this attentional preference for older children might be present during the whole second half of the first year of life, it becomes more robust and evident at around 12 months of age. This attentional preference was mirrored by parental reports. In contrast to studies showing the sensitivity of infants’ banging to different visual stimuli (Sanefuji et al., 2005, 2006), infants banged their arms regardless of the stimuli when viewing the video sequences in the present study. Furthermore, unlike the 12-month-olds, no consistent effects of model age group were found in 6- and 9-month-old infants, except that parental reports regarding 6- and 9-month-olds indicated an attentional preference for peers and older children over adults. Since infants at 6 and 9 months of age are known to be more fearful when viewing an unfamiliar adult as compared to an unfamiliar child (Greenberg, Hillman, & Grice, 1973), the parental report about a preference for peers and older children might be also motivated by the infants’ avoidance of unfamiliar adults. One possible interpretation of the pattern of results obtained is that the 12-month-olds’ attentional preference for older children might be based on their own emerging ability to imitate actions of others. Imitative abilities increase rapidly between 9 and 12 months of age (Carpenter, Nagell, & Tomasello, 1998). As a consequence, 12-month-olds preferably watch object-related actions of older children because older children are within the zone of proximal development (Vygotsky, 1978), and have cognitive and sensorimotor skills that these infants are about to develop. However, because in Experiment 1 both the models’ face and upper body was visible, the infants might have attended primarily to the models’ faces rather than to their actions. For this reason, in many studies on action understanding, infants only see a person’s torso in order to exclude this face bias (e.g., Daum, Prinz, & Aschersleben, 2008; Falck-Ytter, Gredeback, & von Hofsten, 2006; Woodward, 1998). Therefore, in Experiment 2 we tested if 12-month-olds still preferably observe the object-related actions of older children if they see only the torso and the hands but not the model’s face in the video sequences of Experiment 1.

3. Experiment 2 Infants were presented with the same video sequences as in Experiment 1, except that we only showed the torso and the hands and not the models’ face. In this experiment, only 12-month-old infants were tested, because this age group was the one that showed a reliable preference for older children.

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3.1. Method 3.1.1. Participants Participants were twenty-seven 12-month-olds (14 girls, 13 boys; M = 12 months 2 days, range = 11;15–12;14). Ten additional infants were not included in the final sample due to fussiness (n = 5), equipment failure (n = 3), inattentiveness (n = 1), or interference by the parent (n = 1). 3.1.2. Stimuli We edited the video sequences used in Experiment 1 to show only the upper body and the hands of the model. A black border was inserted into the videos using the software Avidemux® so that only the lower half of the video was visible. Thus, the faces and shoulders of the models could not be seen. The display size of the video sequences of the three model age groups were equivalent. Consequently, infants only saw the torso and the hands but not the model’s face. Similar to Experiment 1, eight 10-s video sequences (4 models × 2 toys) displaying only the upper part of the body, without sound, were prepared for each model age group. 3.1.3. Test environment, apparatus and measurement The test environment and the apparatuses used were as in Experiment 1. A second, independent observer recoded 25% of the infants using the video recording. Good levels of inter-rater reliability were obtained for looking time (r = .93, Intraclass correlation). 3.1.4. Procedure The procedure of Experiment 2 was identical to that followed in Experiment 1. 3.2. Results 3.2.1. Heart rate The mean heart rates for the different model age groups (peers, older children, adults) were 126.2 bpm (SD = 8.9 bpm), 126.2 bpm (SD = 10.3 bpm), and 126.2 bpm (SD = 10.4 bpm), respectively. An ANOVA with repeated measurement revealed no reliable effect of model age group (F(2, 24) = .01; p = .99). 3.2.2. Looking time The percentages of looking time for the different model age groups (peer, older child, adult) were 70.5% (SD = 13.1%), 78.6% (SD = 11.3%), and 75.1% (SD = 15.4%), respectively. An ANOVA with repeated measures indicated an effect of model age group (F(2, 24) = 4.56; p < .05). Separate t-tests showed that 12-month-olds looked longer at the video sequences of older children than at video sequences of peers (t(26) = 3.50; p < .01). However, there was no difference between looking times to peers and adults (t(26) = 1.58; p = .12), and no difference in looking times to older children and adults (t(26) = 1.25; p < .22). 3.2.3. Banging The mean number of bangs for the peer, older child, and adult models were 3.3 (SD = 4.9), 2.7 (SD = 4.2), and 2.7 (SD = 4.1), respectively. An ANOVA with repeated measures indicated no effect of model age group (F(2, 24) = .41; p = .67). 3.3. Discussion In Experiment 2, infants showed similar looking-behavior as the infants in Experiment 1, where longer looking times for older children were not influenced by the view of the model’s face. However, contrary to what was found in Experiment 1, infants did not differ in their heart rate when viewing the video sequences of the various age groups. The lack of any differentiation in the psychophysical data could be for one of two reasons. Infants might have preferably observed older children, but we did not find this preference in our heart rate data because looking behavior and psychophysical measures are not perfectly matched (Lansink & Richards, 1997). Alternately, and more likely, obscuring the models’ faces reduced the number of age-related cues and resulted in a weaker attentional preference for older children. Before coming to the conclusion that infants exhibit an attentional preference for older children’s object-related actions, we put two alternative possibilities that might explain this preference to the test. First, an attentional preference for object-related actions of older children might be based merely on their visual appearance and not on the actions they demonstrated. Second, although eight stimuli were designed for each model age group, video sequences of the three model age groups might have contained a different amount of movement and therefore attracted attention differently. Thus, Experiments 3a and 3b were conducted to explore these alternative explanations. 4. Experiment 3a In some studies that used drawings and photographs as stimuli, it was reported that infants differentiate between various age groups (Bigelow, MacLean, Wood, & Smith, 1990; Sanefuji et al., 2006). To control for such a preference, we designed


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Experiment 3a and investigated whether the mere visual appearance of older children could be the reason for the longer mean looking time and lower mean heart rate obtained in Experiment 1. Therefore, we presented still images extracted from the video sequences of Experiment 1. 4.1. Method 4.1.1. Participants Participants were twenty-seven 12-month-olds (10 girls, 17 boys; M = 11 months 26 days, range = 11;15–12;15). Twentytwo additional infants had to be excluded due to inattentiveness (n = 8), fussiness (n = 7), equipment failure (n = 6), or interference by the parent (n = 1). The high number of drop-outs is probably due to the fact that the still images we presented were not as interesting as the video sequences presented in Experiment 1. As a consequence, some infants did not look at the monitor and there was sometimes slightly increased motor activity (e.g., because they tried to get off their parents’ laps). If the electrodes became detached because of increased motor activity, we labeled the exclusion criterion of these infants “equipment failure”. If an infant did not look at the monitor at least once during the presentation of one video sequence, we excluded this infant from the data set and labeled the exclusion criterion “inattentiveness”. 4.1.2. Stimuli We extracted still images from the video sequences of Experiment 1. All models held a toy in their hand and focused either on the object itself or a point approximately 1 m beside the camera. In doing so, the models never looked in the participating infant’s eyes. Similar to Experiment 1, eight 10-s video sequences (4 models × 2 toys) with still images were prepared for each model age group. 4.1.3. Test environment, apparatus and measurement The test environment and the apparatus used were as in Experiment 1. A second independent observer recoded 25% of the infants using the video recording. Good levels of inter-rater reliability were obtained for looking time (r = .97, Intraclass correlation). 4.1.4. Procedure The procedure of Experiment 3a was comparable to Experiment 1 with the following exception. Due to infants’ reduced interest in the static stimuli, we presented only 3 rather than 6 models. Accordingly, the duration of stimulus presentation decreased by 50%. 4.2. Results 4.2.1. Heart rate The mean heart rates for the different model age groups (peer, older child, adult) were 123.7 bpm (SD = 10.7 bpm), 124.9 bpm (SD = 11.1 bpm), and 124.3 bpm (SD = 9.7 bpm), respectively. An ANOVA with repeated measures revealed no reliable effect of model age group (F(2, 24) = .36; p = .70). 4.2.2. Looking time The percentages of looking time for the different model age groups (peer, older child, adult) were 58.7% (SD = 22.38%), 63.8% (SD = 16.4%), and 64.5% (SD = 17.9%), respectively. An ANOVA with repeated measures indicated no effect of model age group (F(2, 24) = 1.06; p = .36). 4.2.3. Banging The mean number of bangs for the peer, older child, and adult models were 1.9 (SD = 3.3), 2.4 (SD = 3.7), and 2.0 (SD = 2.2), respectively. An ANOVA with repeated measures indicated no effect of model age group (F(2, 24) = .16; p = .82). 4.3. Discussion From these results, we can conclude that mere visual appearance is not sufficient to elicit a selective interest for older children in 12-month-olds. 5. Experiment 3b As noted above, one could argue that the video sequences of the three model age groups might have contained a different amount of movement and therefore attracted infant attention differently. This alternative interpretation of the results obtained in Experiments 1 and 2 was tested in the present experiment by showing a scrambled version of the original videos, resulting in the overall amount of movement in the videos remaining the same but the identity and age of the actors not being transparent any more.

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5.1. Methods 5.1.1. Participants Participants were twenty-seven 12-month-olds (14 girls, 13 boys; M = 12 months 5 days, range = 11;20–12;15). Twentythree additional infants were not included in the final sample due to inattentiveness (n = 9), fussiness (n = 7), equipment failure (n = 5), or interference by the parent (n = 2). As in Experiment 3a, this high dropout rate might have been caused by the fact that the video sequences were not as interesting as in Experiment 1, this time because they only showed a scrambled version of the original videos. 5.1.2. Stimuli We transformed the video sequences used in Experiment 1 into video sequences with a mosaic pattern using the Software EDIUS Pro 3.0® (Canopus Co., Ltd., San Jose, CA, USA). The size of each mosaic was 18 × 18 pixels. This transformation ensured that the unspecific activity remained in the video sequences. However, the mosaic video sequences concealed the fact that a human being caused this activity. As in Experiment 1, eight 10-s video sequences (4 models × 2 toys) with mosaic pattern, without sound, were prepared for each model age group. 5.1.3. Test environment, apparatus and measurement The test environment and the apparatuses used were as in Experiment 1. A second independent observer recoded 25% of the infants using the video recording. Good levels of inter-rater reliability were obtained for looking time (r = .96, Intraclass correlation). 5.1.4. Procedure The procedure was identical to that followed in Experiment 1. 5.2. Results 5.2.1. Looking time The percentages of looking time for the different model age groups (peers, older children, adults) were 59.6% (SD = 16.4%), 63.6% (SD = 16.1%), and 60.1% (SD = 17.4%), respectively. An ANOVA with repeated measures indicated no effect of model age group (F(2, 24) = .97; p = .39). 5.2.2. Heart rate The mean heart rates for the different model age groups (peers, older children, adults) were 131.4 bpm (SD = 8.6 bpm), 131.2 bpm (SD = 9.4 bpm), and 131.6 bpm (SD = 8.4 bpm), respectively. An ANOVA with repeated measures revealed no reliable effect of model age group (F(2, 24) = .11; p = .90). 5.2.3. Banging The mean number of bangs for the peer, older child, and adult models were 6.9 (SD = 9.5), 3.9 (SD = 5.4), and 6.3 (SD = 8.1), respectively. An ANOVA with repeated measures indicated no effect of model age group (F(2, 24) = 1.94; p = .15). 5.3. Discussion Experiment 3b, in which modified video sequences of Experiment 1 with mosaic patterns were used, no longer revealed a preference for the video sequences with older children. Thus, we can conclude that the overall motor activity that was displayed in the video sequences in Experiment 1 is not sufficient to elicit a selective interest in older children in 12-montholds. 6. General discussion In the present study, we investigated whether infants exhibit an attentional preference for a specific age group performing object-related actions. In contrast to previous studies, infants in the first years of life showed an attentional preference for older children performing object-related actions (Experiment 1). This effect became robust at 12 months of age. The attentional preference for older children relies at least partially on the actions themselves and not on any age-related cues provided by the models’ faces (Experiment 2). Control experiments ruled out the possibility that this is an attentional preference for the visual appearance of older children (Experiment 3a) or that the finding can be traced back to the general amount of activity of the differently aged models (Experiment 3b). In accordance with Rothstein-Fisch and Howes (1988), we assume that older children provide both a level of similarity as well as increased competence that creates a zone of proximal development for their younger cohorts (Vygotsky, 1978). Therefore, 12-month-olds might have preferred watching older children’s object-related actions in order to learn from them. The lack of attentional preference for older children in the group of 6- and 9-month-olds might be due to the object manipulation demonstrated. Object use becomes increasingly important at the end of the first year of life (Vandell, Wilson,


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& Buchanan, 1980) as does imitation of object-directed actions (see Anisfeld, 2005 for a review). Tomasello, Carpenter, Call, Behne, and Moll (2005) recently pointed out that by 14 months of age, infants start to imitate actions based on their analysis of what kind of means are necessary to achieve a certain goal. This form of social learning is regarded as the beginning of cultural learning (Tomasello et al., 2005). Recent research has shown that 12-month-olds are already capable of this kind of social learning (Schwier, Van Maanen, Carpenter, & Tomasello, 2006; Zmyj, Daum, & Aschersleben, 2009). Thus, the attentional preference for older children who provide an action repertoire which infants are about to develop might be a adaptive strategy for acquiring new skills from the age of 12 months on. This interpretation is in line with imitation studies showing that 1-year-olds imitate older children more accurately and more often than adults (Ryalls, Gul, & Ryalls, 2000; for different findings, however see Seehagen & Herbert, 2011; Zmyj et al., in press). With the present study, our aim was to look more closely at infants’ attentional preferences for differently aged models. We followed this aim by using a more objective additional dependent measure (i.e., heart rate) and by using stimuli (i.e., video sequences of simple object-directed actions) that were more ecologically valid than those used previously. Three main implications are related to these changes of stimuli and dependent measures. First, Sanefuji et al. (2005, 2006) emphasized the role of banging in the measurement of infants’ attentional preference. Based on these findings, we expected a close link between infants’ banging rate on the one hand, and looking time, heart rate and parental report on the other. However, we did not find banging to be indicative of the infants’ attentional preference. This might be a result of the multiple motives that are behind an infant’s banging. As Behne et al. (2005) pointed out, banging also signifies frustration, while Thelen (1980) suggested that banging is related to the development of the sensorimotor function. Thus, in our study, infants’ banging might have been driven by one of these opposite motives and not necessary by attentional preferences. This might be a reason why no effect was found in this domain in the present study. To further qualify these inconclusive results, in the present study, infants’ heart rate was also measured. Since heart rate has been shown to be closely related to attention (Richards & Casey, 1991), we believe that our results are less ambiguous than studies using such purely behavioral responses. Second, in contrast to a few previous studies (Lewis & Brooks-Gunn, 1975; McCall & Kennedy, 1980; Sanefuji et al., 2005 Experiment 2), we did not find an attentional preference for peers when presenting video sequences or still images. We assume that this finding might be related to our use of a different method of presenting the models. Most previous studies used close-up views of the faces, where babyish characteristics are more obvious than in the video sequences and the still images we used. In the present study, the dynamic presentation of sequences of object-related actions might have drawn more attention to the actions themselves. As Experiment 2 has shown, the present findings are at least partially based on the perception of the models’ action and not the face. In addition, in virtually all previous studies in this area, drawings, photographs or still images were used as stimuli (Lewis & Brooks-Gunn, 1975; McCall & Kennedy, 1980; Sanefuji et al., 2005 Experiment 2). To our knowledge, only Sanefuji et al. (2005, Experiment 1) used video stimuli of differently aged models and reported a preference for peers based on infants’ increased banging when viewing these age groups, which was interpreted as a sign of interest. However, as described above, the interpretation of banging behavior is inconsistent (Behne et al., 2005; Thelen, 1980). Accordingly, it is not clear whether Sanefuji et al.’s (2005) data relating to banging responses contradicts our finding showing attentional preference for same aged peers (interest account, Sanefuji et al., 2005), whether it is line with our findings as it shows less attentional interest in same aged peers compared to older children (frustration account, Behne et al., 2005), or whether it is not related to attention and hence to our findings at all, as suggested by our own data and by Thelen (1980). One might further assume that when infants watch other individuals in action, they preferentially observe older children in order to learn about these actions. In contrast, when infants perceive salient babyish characteristics infants might preferably watch peers. Before we can use banging as valid source of information about infants’ attention we need to know more about how to distinguish such different kinds of motivations that underlie infants’ banging. To sum up, in the present study, we showed that infants in the first year of life exhibit an attentional preference for older children acting with objects compared to peers and adults acting with objects. This selective preference is strongest at around the age of 12 months. This is the age when infants become especially interested in various object-related actions (Rothstein-Fisch & Howes, 1988) performed by more experienced models, who are in the zone of proximal development (Vygotsky, 1978). 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