Teach to Reach: The Effects of Active Versus Passive ReachingExperiences on Action and Perception

Klaus Libertus1 and Amy Needham21 Psychology & Neuroscience, Duke University, Durham, NC 27708, USA2 Psychology & Human Development, Vanderbilt University, 230 Appleton Place, Nashville, TN37203, USA

AbstractReaching is an important and early emerging motor skill that allows infants to interact with thephysical and social world. However, few studies have considered how reaching experiences shapeinfants’ own motor development and their perception of actions performed by others. In thecurrent study, two groups of infants received daily parent guided play sessions over a two-weektraining period. Using “Sticky Mittens”, one group was enabled to independently pick up objectswhereas the other group only passively observed their parent’s actions on objects. Followingtraining, infants’ manual and visual exploration of objects, agents, and actions in a live and atelevised context were assessed. Our results showed that only infants who experiencedindependent object apprehension advanced in their reaching behavior, and showed changes in theirvisual exploration of agents and objects in a live setting. Passive observation was not sufficient tochange infants’ behavior. To our surprise, the effects of the training did not seem to generalize to atelevised observation context. Together, our results suggest that early motor training can jump-start infants’ transition into reaching and inform their perception of others’ actions.

KeywordsInfant perception; motor development; perception-action; sticky mittens

An important and yet little studied question in development is how new abilities build uponexisting abilities. Developmentalists are often criticized for collecting snapshots of staticabilities: indeed, few methods have been devised that allow us to see developmental changein action and measure the consequences of these changes. However, development is adynamic process that can be shaped by experiences and it is evident that infants readily learnfrom their own actions (e.g., Adolph, 1997; Campos, et al., 2000; DeCasper & Carstens,1981; Rovee & Rovee, 1969).

As infants grow and acquire new motor skills, their behaviors and interactions with theworld around them change. Attaining new motor skill provides infants with access to newkinds of information and opportunities for learning (Bushnell & Boudreau, 1993; Gibson,1988). For example, manual exploration strategies determine the kind of information (e.g.,

Corresponding Author: Klaus Libertus, Duke University, Box 90086, Durham, NC 27708, Phone: 919-660-8754, Fax: 919-660-5726,Klaus.libertus@duke.edu.Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to ourcustomers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review ofthe resulting proof before it is published in its final citable form. Please note that during the production process errors may bediscovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Published in final edited form as:Vision Res. 2010 December ; 50(24): 2750–2757. doi:10.1016/j.visres.2010.09.001.

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shape, texture, or weight) that can be obtained from an object (Lederman & Klatzky, 2009).Advances in postural control increase infants’ interest in objects, ending a period ofexclusive face-to-face interactions between mother and infant (Fogel, Messinger, Dickson,& Hsu, 1999). Once infants start to independently engage in manual exploration, they showmore advanced object segregation abilities (Needham, 2000) and pay more attention tointermodal properties of objects (Eppler, 1995). Similarly, self-produced locomotion altershow infants respond to and interact with others (e.g., Bertenthal, Campos, & Kermoian,1994; Clearfield, Osborne, & Mullen, 2008). Following the onset of independent walking,infants engage in more interactive exchanges with their mother (Clearfield, 2010) and showmore expressions of emotion (Biringen, Emde, Campos, & Appelbaum, 1995). Thesefindings suggest that acquiring a new motor skill can have influences across differentdomains of development. However, studies by Adolph and colleagues also show thatlearning from motor experiences can be quite specific and does not necessarily generalize tonovel situations (e.g., Adolph, 1997; Adolph, 2000; Adolph & Berger, 2006). It remainsunclear what exactly infants learn from motor experience and how far-reaching this learningreally is.

Piaget suggested that self-produced action experiences also contribute the formation ofaction representations (Piaget, 1953). A number of studies have now shown that first-handaction experiences influence infants’ perception and understanding of actions (for review seeHauf, 2007). For example, infants’ ability to identify the goal of an observed action seems todepend on their own ability and experience (natural or artificial) with performing the sameaction (Sommerville & Woodward, 2005; Sommerville, Woodward, & Needham, 2005).Further, infants’ own actions on an object seem to increase their interest in actionsperformed by others on the same object (Hauf, Aschersleben, & Prinz, 2007). Recentfindings show that the amount of self-produced object exploration is related to how quicklyinfants’ orient towards static faces (Libertus & Needham, submitted).

Neurophysiological studies support the involvement of the motor system in actionobservation. A mirror matching or mirror-neuron system (MNS) has been proposed as apotential neurological basis for the link between action and perception (Rizzolatti &Craighero, 2004). Studies with adults and infants have shown that action experiences andexpertise can modulate the response of the MNS (Cross, Hamilton, & Grafton, 2006; vanElk, van Schie, Hunnius, Vesper, & Bekkering, 2008). Further, already in infancy the motorsystem seems to be involved in predicting the outcome of observed actions (Stapel, Hunnius,van Elk, & Bekkering, 2010). Together, behavioral and neurophyisological findings suggestthat changes in infants’ own motor abilities may influence their perception of objects, actors,and actions.

However, determining the unique contributions of experiences on development ischallenging. Assessing infants’ behavior once they have independently acquired a newmotor skill leaves open the possibility that some general maturational processes may havecaused both the acquisition of new motor skills and the changes in behavior. Age is acommonly used estimate for maturation, but age is confounded with experience. Even withage held constant, there are considerable differences between infants with regard to theirskills and experiences. For example, while some infants start walking by eight months,others only start around 15 months of age (de Onis, 2006). When assessing behavior in 12-month-old infants, about half of the infants will have experienced walking for a month orlonger whereas the other half will not have engaged in walking at all.

To study the effect of experiences while avoiding confounding influences of age, one cancompare infants of the same age but with different levels of expertise (e.g., crawling andnon-crawling seven-month-olds). Using this approach, studies have shown that infants’

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behavior is greatly affected by their first-hand experiences (e.g., Campos, Bertenthal, &Kermoian, 1992). However, experimenters cannot randomly assign infants to the early-crawling and late-crawling groups. Thus, unknown factors could explain differencesbetween the groups.

One way to address the issue of unknown confounding factors is to artificially alterexperiences in same-age infants. A classic example of this approach is the kitten carouselstudy by Held & Hein (1963). Here, kittens were raised in the dark except for brief episodesin a patterned environment. Kittens were either allowed to actively move though thepatterned environment or they only passively observed the environment from a sled that waspulled by a kitten from the active group. Both groups experienced roughly the same amountof visual stimulation, but only in the active group was the visual input contingent on thekitten’s own movement. A subsequent test using the “visual cliff” apparatus (Gibson &Walk, 1960) showed that only the actively-obtained visual experience shaped kittens’visually-guided behaviors. This experiment demonstrated, very impressively, that self-produced actions and contingent feedback provide necessary information required for thedevelopment of (in this case) visually-guided behaviors.

The impact of active experiences on development has also been observed with humaninfants. For example, providing infants who cannot yet reach for objects themselves withreaching experience using ‘sticky mittens’ facilitates exploration behavior and actionunderstanding (e.g., Needham, Barrett, & Peterman, 2002; Sommerville, et al., 2005).However, it is still unknown whether the changes following reaching training are due to theactual physical experience with reaching actions or due to other aspects of the training (suchas context, exposure to objects, engagement with the parent or experimenter, or theencouragement provided by the parent). The current research addresses this issue byinvestigating the effects of active and passive reaching experiences (see Figure 1) on infants’manual and visual exploration of objects, actors, and actions.

The goal of the current research is to investigate the influences of active and passive ‘stickymittens’ training experiences on infants’ manual and visual exploration of objects, actors,and actions. We report longitudinal changes in manual exploration behavior (sampling 5–6times over a two-week period) and compare infants’ visual exploration of objects, actors,and actions in a live (action possible) and televised (observation only) context. Our analysisfocused on reaching and grasping behavior, two important developmental milestones thatenable infants to obtain objects for further inspection on their own. Despite earlier reports ofreaching in newborns (Bower, Broughton, & Moore, 1970), most of the time newborns donot succeed in contacting or obtaining objects with their “prereaching” attempts (vonHofsten, 1982). Successful independent reaching does not emerge until about four to fivemonths after birth (Pomerleau & Malcuit, 1980; von Hofsten & Ronnqvist, 1988).Therefore, the present study tested three-month-old infants who were not able to reach forobjects on their own yet.

We predicted that active reaching experience would facilitate reaching and graspingbehavior and heighten infants’ attention towards others’ actions (see Needham, et al., 2002;Sommerville, et al., 2005). We did not predict that passive reaching experiences wouldfacilitate reaching and grasping behavior but expected that passive action observation wouldstill increase infants’ attention to and understanding of others’ actions since infant’srepeatedly observed similar actions. It is currently unknown whether self-produced actionexperiences also influence the perception of others’ actions in a televised context. Childrenseem to show more difficulties understanding televised events (Troseth & DeLoache, 1998).However, at least by 6 months of age infants process televised and live events similarly

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(Hofer, Hauf, & Aschersleben, 2007). Therefore, we predicted that self-produced actionexperiences would alter perception of others’ actions in both a live and a televised context.

MethodParticipants

Participants were 58 full-term infants from four groups: two trained groups and two naïvecomparisons groups (see Table 1 for details). The “Active Training (AT) group consisted of18 two- to three-month-old infants who were trained using “Sticky Mittens” forapproximately two-weeks. The “Passive Training” (PT) group similarly consisted of 18 two-to three-month-old infants who observed their parent grasp and move objects forapproximately two-weeks. A control group of 19 three-month-old infants that received notraining (NT3) was additionally recruited. Finally, a control group of 23 five-month-oldinfants that received no training (NT5) was recruited to compare performance on the visualexploration task.

Nine infants did not complete the televised-context assessment due to fussiness (AT=3, PT =1, NT3 = 2, NT5 = 3) and three different infants from the NT3 group did not complete thelive-context assessment due to fussiness (n = 1) or technical difficulties with the recordingequipment (n = 2).

StimuliLive context—Manual and visual exploration in a live context were assessed using a smallinfant rattle that was easily graspable (0.8×6.4×11.5 cm, H×W×D). While infants weresitting on their parent’s lap, the rattle was presented on a reaching table with a half-circle(radius 23 cm) cut out on the infant’s side (lab visits) or on a reaching tray (home visits; seeFigure 2). The reaching tray measured about 30 × 40 cm and had a similar half-circle (radiusabout 14 cm) cut out. The tray ensured similar testing situations during home and lab visits.

Televised context—Visual exploration in a televised context was assessed using eightshort (23 sec.) video clips presented on a 17” computer screen. In the video clips, an actorwas seen with her right hand resting on a table. A bright and salient toy was on the left orright side of the table. After 5 seconds, the actor grasped the toy with her right hand fromabove and either lifted the toy straight up or slid the toy across the table (either action lasted5 seconds). Following the action, the actor’s hand returned to its starting position andremained static for 5 seconds. During this sequence the actor looked down at the table infront of her.

Two different toys were used, an orange box with large blue dots and a yellow hexagon withtwo blue stripes and several small blue dots. Each toy was lifted twice and slid from left toright once and from right to left once. Movies were separated by a fixation stimulus. Theactions used in the video clips were similar to actions infant’s would observe in the passivetraining procedure where parents grasped objects, moved objects over to one side, and liftedobjects.

ApparatusSticky Mittens—Custom-made infant mittens with Velcro® (loop) sewn to the palm(“Sticky Mittens”, see Needham, et al., 2002) were placed on infants’ hands during trainingin both the AT and PT groups.

Training toys—A set of six Duplo® blocks were used as training toys in both the AT andPT group. Blocks measured 4.5 cm on each side with a round dome on top and were

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grouped into three sets of the same color (a singleton, a pair and a triplet). For the AT group,small squares of Velcro® (hook) were attached to the blocks, making them stick to themittens. For the PT group, small squares of electrical tape were attached to the blocks,making them appear visually similar to the blocks in the AT group. In the PT group, theblocks would not stick to the mittens upon contact.

Eye Tracking—Eye gaze during visual exploration in a televised context was recordedusing a remote eye tracker (Tobii 1750). Eye-tracking sessions were conducted in a dimly litroom with the infant sitting in a semi-reclined “bouncy chair” about 60 cm away from a 17”computer screen. To the infant’s right there was a wall covered with black fabric and on theinfant’s left there were two large pieces of cardboard also covered with black fabric. Boththe experimenter and parent were in the same room but hidden from the infants’ view.

ProcedureTraining—In the AT and PT groups, parents were asked to train their infants for 10minutes each day for a two-week period. Training started on the first lab visit with anexperimenter-led demonstration session. Parents then took home all training materials andprinted instructions. All remaining training sessions were parent-led except for shortexperimenter-led training sessions during home-visits to clarify the procedure.

In the AT group, one set of the training blocks (sticky) were first placed in front of theinfant. Parents then demonstrated once (per set) that the blocks would stick to the infant’smittens, placed the blocks back on the table, and drew attention to the blocks by pointing,touching, or commenting about the blocks. Infants had to reach out for the blocksthemselves and were allowed to manipulate and shake the blocks for about 10 secondsfollowing contact (see Figure 1a). The blocks were then placed back on the table and thesequence was repeated until a total of 10 minutes had passed (rotating thought the 3 sets ofblocks).

The PT group was trained using an “Object Dance” procedure. One set of training blocks(non-sticky) were first placed in front of the infant and parents drew attention to the blocks.Parents then lifted one block, tapped it briefly on the table, moved over to the infant’s lefthand, tapped the block on the table again, lifted the block to eye level and briefly touchedthe palm of the infant’s hand with the block (see Figure 1b). The block was then returned toits starting position and the same sequence was repeated on the infant’s right side. Thisprocedure was repeated until a total of 10 minutes had passed. The PT group experiencedsimilar levels of exposure to the training materials (mittens and blocks) as the AT group butdid not engage in self-produced reaching. Wearing mittens in the PT group did preventinfants from grasping and manipulating the training toys (by covering the fingers). Thus,infants in this group were not able to experience self-produced reaching during training.

Assessments—Exploration behavior was assessed in a live context and a televisedcontext. In the live context, a four-step reaching assessment (Figure 2) was used to measuremanual and visual exploration in the NT3, AT, and PT groups. The NT5 group did notcomplete this assessment because their performance was expected to be at ceiling. The NT3group completed this assessment once. The AT and PT groups completed this assessment 5–6 times, once each lab visit (before training and after two-weeks of training) and on up to 4home visits (see Table 1). Home visits were conducted every 2–4 days during the two-weektraining period.

During the four-step reaching assessment, a toy was sequentially placed beyond reach, thenfar but within reach, then next to the hand, and finally inserted into the infant’s hand (seeFigure 2 for schematic). If the infant dropped the toy immediately, up to 3 further attempts

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were made to place the toy into the infant’s hand. The four steps were always performed inthe same order (Beyond, Far, Close, Holding) and each step lasted approximately 30seconds before the experimenter moved on to the next step.

In the televised context, visual exploration was assessed once in all groups. The televisedassessment was always conducted before the live-context assessment. In the AT and PTgroups, the televised assessment was conducted following two-weeks of training on lab visit2.

MeasuresLive context—The four-step reaching assessment provided infants’ with differentopportunities to interact with the toy. During Step I, infants could only passively look at thetoy. Here, our analysis focused on infants’ visual attention to the toy and the experimenter.During both Steps II and III, the toy was placed within reach these steps were combinedfocus infants’ reaching and grasping actions. During Step IV, the toy was placed into theinfant’s hands and no reaching was necessary. Here, our analysis focused on how frequentlyinfants shifted their visual attention back and forth from the toy (looking episodes).

Televised context—The televised-context assessment provided similar measures as StepsI and IV of the live-context assessment: 1) attention to the toy or the actor (see Step I live),and 2) shifts in attention between the actor’s face and the toy (see Step IV live). Thisenabled us to compare visual exploration across different contexts: Live observation (StepI), Live hands-on (Step IV), and Televised observation. Eye tracking allows for more fine-grained analyses than looking-duration and switches (e.g., anticipation, latency). However,for comparison between live and televised context we decided to focus on measures thatwere available in both contexts for the present analysis.

CodingInfants’ motor behavior was coded by trained observers using frame-by-frame codingsoftware (Libertus, 2008). The following behaviors were assessed: looking at the toy or atthe experimenter or elsewhere, reaching for the toy (extending hands towards toy whilelooking at it), touching the toy, grasping the toy (touching toy and bringing one corner of thetoy off the table), bi-manual exploration, swatting at the toy, and mouthing the toy. Twodifferent observers coded a random sample of 41 trials using frame-by-frame codingsoftware and overall reliability was high (r = .90). To control for spurious oversampling andto compare our coding method to previous approaches, all data from the second lab visit(AT, PT, and NT3 groups, total 208 trials) were coded for looking at the toy and touchingthe toy using real-time coding software (see Needham, et al., 2002). Correlations betweenthe different coding methods were high (touching: r = .90; looking: r = .75). For all analysesreported here, scores of the frame-by-frame coding procedure were used.

ResultsLive-context assessment

Following the training period, infants in the AT group showed a decrease in attentiontowards the experimenter on Step I of the manual task, an increase in reaching and graspingbehavior on Steps II and III, and an increased number of looking episodes to the toy on StepIV. Results are shown in Figure 3 and reported as proportions of the total trial duration.Gender differences have been reported for early motor behavior with males being moreactive than females (Eaton & Enns, 1986) but females showing faster and more accurateneonatal imitation skills (Nagy, Kompagne, Orvos, & Pal, 2007). Therefore gender was

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controlled for in all analyses by inclusion as factor. No effects of gender were found in thisstudy.

Between-group differences were of key interest for our analysis. Therefore, on each of thelab visits, percentage scores were compared using a 2 (Gender) × 3 (Group) between-subjects analysis of variance (ANOVA). Because not all infants completed all home-visits,the AT and PT groups were compared to each other on each home visit via separate 2(Gender) × 2 (Group) ANOVAs. On all measures, no significant group differences beforetraining (all ps > .340) were observed. Changes from before to after training (lab 1 vs. lab 2)were expected a priori based on previous findings (see Needham, et al., 2002) and weperformed unadjusted (and more powerful) t-test for these within-group comparisons.

Step I – Looking behavior—On Step I of the manual assessment, no group differenceswith regard to infants’ attention towards the toy were present following training (p = .361).Across the three groups, infants spent about the same amount of time looking at the toy(approximately 65% of the time; other options were experimenter, parent, or distracted).However, looking behavior differed when infants were looking at the experimenter.Significant differences between the AT (M = 6.07%, SD = 9.20) and the PT (M = 28.83%,SD = 29.03) group were present on the 3rd home visit (F(1,32) = 9.439, p = .004, η2 = .227).On the 2nd lab visit, an ANOVA indicated significant between-group differences (F(2,46) =3.709, p = .032, η2 = .157) and planned between-group comparisons revealed that infants inthe AT group (M = 3.22%, SD = 6.41) spent less time looking at the experimenter thaninfants in the PT group (M = 19.26%, SD = 27.97, p = .012, 95% CI [−28.39, −3.67]).Within-group analyses of behavior before and after training showed a borderline significantdecrease in looking at the experimenter for the AT group (t(17) = 2.082, p = .053) but noeffects in the PT group (t(17) = −1.054, p = .307).

Steps II and III – Reaching and Grasping behavior—On Steps II and III of themanual assessment, group-level differences were observed by the 3rd home visit where theAT group (M = 23.82%, SD = 29.66) showed significantly more reaching and graspingbehavior than the PT group (M = 8.13%, SD = 13.12; F(1,32) = 4.380, p = .044, η2 = .128).Similarly, on the 4th home visit the AT group (M = 25.39%, SD = 28.00) showed morereaching and grasping behavior than the PT group (M = 7.56%, SD = 10.04; F(1,28) =5.705, p = .024, η2 = .164). Finally, on the 2nd lab visit, an ANOVA revealed significantbetween-group differences (F(2,46) = 4.380, p = .018, η2 = .156) and planned comparisonsindicated that infants in the AT group (M = 29.93%, SD = 27.42) engaged in more reachingand grasping than infants in the PT group (M = 11.79%, SD = 14.69; p = .009, [4.70,31.57]). Within-group analyses of behavior before and after training revealed a significantincrease in reaching and grasping for the AT group (t(17) = 3.875, p = .001) but not for thePT group (t(17) = 1.149, p = .266).

Step IV – Looking Episodes—On Step IV of the manual assessment, there were nogroup differences with regard to infants’ attention towards the toy or towards theexperimenter following training (both ps > .598; but there was a significant effect of genderwith males looking more at the experimenter than females). There were differences in howoften (# of looking episodes) infants looked at the toy. On the 2nd home visit, the infants inthe AT group (M = 3.44, SD = 2.28) produced more separate looking episodes to the toythan infants in the PT group (M = 1.61, SD = 1.14; F(1,32) = 8.630, p = .006, η2 = .206). Onthe 2nd lab visit, an ANOVA revealed a significant effect of group (F(2,46) = 3.594, p = .035, η2 = .123) and planned between-group comparisons indicated that the infants in the ATgroup (M = 3.44, SD = 2.28) showed more looking episodes than the infants in the PT group(M = 1.72, SD = 1.78; p = .011, [0.42, 3.03]). Within-group analyses of behavior before and

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after training confirmed a significant increase in the number of looking episodes for the ATgroup (t(17) = −2.257, p = .037) but not for the PT group (t(17) = −0.270, p = .790).

Televised-context assessmentAcross all groups, there were no between-group differences in infants’ attention to theactor’s face or the toy during observation of televised actions (both ps > .164). However,there was a significant effect of group with regard to the number of gaze shifts (switches)infants produced between the face and the toy (F(3,61) = 2.847, p = .045, η2 = .115). Post-hoc comparisons between all groups (Tukey HSD) revealed that the older NT5 group (M =28.45, SD = 19.30) produced significantly more switches than the NT3 group (M = 14.71,SD = 10.72; p = .029, 95% CI [1.06, 26.43]). No other group comparisons were significant(all ps > .268). Five-month-olds produced the highest number of gaze shifts between the toyand the face followed by the infants in the AT group (see Figure 4).

Comparison: Live vs. Televised contextInfants’ attention to the face or the toy were assessed across three different contexts: in alive setting with the infant being a passive observer (Step I of the manual task), in a livesetting with the infant actively manipulating the toy (Step IV of the manual task), and in atelevised setting with the infant being a passive observer (visual task). The events observedin the live and televised context were not identical. Therefore, live and televised contextcannot be compared directly. However, influences of context are still of interest and aresummarized in Table 2. Regardless of the training experience, changes in context seemed tohave similar influences on infants’ behavior with an increase in attention towards faces overtoys in the televised context.

DiscussionThe results reported here show that “Sticky Mittens” training encourages infants’ reachingand grasping behavior and changes their visual exploration of actors and objects in a livecontext. Two groups of three-month-old infants experienced approximately two hours ofobject directed training over a two-week period using different training procedures that weredesigned to be highly similar to each other. The two procedures only differed with regard tothe infants’ own actions. In the Active-Training (AT) group, infants were able to contact andmove objects themselves. In the Passive-Training (PT) group, infants observed the objectsbeing moved and touched to their hands by their parents. Emphasizing the role of self-produced motor experiences in development, this seemingly small difference in procedureled to significant differences in behavior.

The idea that motor development influences perceptual and cognitive development is notnew. Piaget described motor skills as a mechanism that drives development in other domainsby generating new sensorimotor experiences (Piaget, 1953, 1954). More recent formulationsof this idea describe our cognition and perception as “embodied” or grounded in the bodyand its actions (e.g., Gibson, 1988; Needham & Libertus, in press; Smith & Gasser, 2005).Nevertheless, it is surprising that infants’ behavior can be changed by only two hours ofself-produced motor experiences distributed over two weeks and that closely matched butpassive experiences are not sufficient. Several studies have shown that infants are highlysensitive to action-outcome relations and readily learn contingencies between their ownbehavior and outcomes in the world (e.g., DeCasper & Carstens, 1981; Rovee-Collier, 1999;Thelen, 1994). Experiencing success with their actions during active training may haveencouraged and motivated infants to reproduce the outcome with different objectsthroughout the day and thereby fostered the development of reaching and grasping skillsbeyond the actual training duration.

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Motor skills are important for development in general and affect what kinds of informationcan be extracted from the environment (e.g.,Bushnell & Boudreau, 1993; Gibson, 1988;Lederman & Klatzky, 2009). Similarly, infants’ engagement in simultaneous visual-manualobject exploration predicts their 3D object completion skills (Soska, Adolph, & Johnson,2010). Our results show that motor experiences affect both infants’ own motor behavior andtheir visual exploration of observed objects, actors, and actions. During observation in thelive context, infants in the AT group showed only little interest in the experimenter whileinfants in the PT group showed considerable interest in the experimenter. This patternmatches the experiences provided by the AT and PT procedure: In the PT group, adultsacted on objects for the infants. In the AT group, infants had to act on objects themselves.When given the opportunity to manipulate a toy in the live context, the AT and PT groupshowed similar interest in the toy and experimenter. However, infants in the AT groupshowed more looking back and forth between toy and the surrounding environment(experimenter, parent, room). Looking back and forth allows infants to compare the toy toother objects and to assess the interest of others in the toy. Thus, infants of the AT groupshowed more interest in actions and interactions between object and environment in a livecontext. This behavior may facilitate learning about the goals and actions of others.

However, we also observed evidence for specificity of learning from self-produced actions.Even though both motor behavior and visual exploration in a live setting were differentbetween the AT and PT groups, no differences were present during observation in atelevised context. Depending on the context experienced by the infant (live vs. televised),visual exploration of objects, actors, and actions seemed to be affected differently by self-produced reaching experiences. Infants in the AT group showed a clear decrease in attentionto actors and an increase in looking episodes to objects in a live setting, but in a televisedcontext these infants were not significantly different from their age-matched peers.

We are not the first to report different results between perception of a live and televisedactions. In a study with 6–7-month-old infants, Shimada and Hiraki (2006) observedsignificantly different brain responses during action-observation and during observation ofobject-motion in a live context but not in a televised context, suggesting that infants processtelevised events differently than live events. Further, learning from televised actions seemsto be harder for young children than learning from live observation (Troseth & DeLoache,1998). Several factors differed between the live and televised context in our study and couldexplain the absence of an effect of motor training on perception during the televised context.

First, it is possible that infants had difficulty understanding actions in the televised contextbecause of the impoverished and unnatural stimulus. Learning from their own actions mightonly generalize to others in similar contexts at first. In previous studies, the context andobjects during training and action observation were highly similar (Sommerville, et al.,2005). This similarity should facilitate comparison processes such as structural alignmentthat could help infants identify correspondences between two scenarios (Gentner & Gunn,2001; Markman & Gentner, 2000).

Second, infants’ action understanding abilities may not generalize across different posturesof the infant. Motor learning is specific to the particular posture experienced during learning(e.g., Adolph, 1997, 2000). In the present study, infants’ posture differed between themanual and visual tasks. During observation in the live context, infants were seated on theirparent’s lap in an upright posture. During observation in the televised context, infants wereseated in a reclined bouncy chair. It is plausible that the infant action understanding systeminitially requires infants to be in a posture that would allow them to perform an actionthemselves in order to become engaged during observation. Supporting this hypothesis,previous studies already observed effects of posture on visual exploration in newborns

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(Fredrickson & Brown, 1975) and one to six month-old infants (Fogel, et al., 1999). We willinvestigate this idea in future research.

The findings reported here inform our understanding of the development of infants’exploratory skills and the connection between these skills and infants’ ability to understandobserved actions. Future studies should investigate the connections between actionexperience and action perception to further clarify the underlying brain circuits. In thisdomain and others, we need to learn more about how experience influences and shapesinfant’s developing abilities.

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Figure 1.Example of the Active- and Passive-Training procedures. a) Active Training (AT): Toysstick to the mittens upon contact and are moved by the infant. b) Passive Training (PT):Toys are moved by the parent and do not stick to the mittens.

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Figure 2.Example of the four-step reaching assessment used in the live context. A small toy wassequentially placed I) beyond reach, II) far but within reach, III) close to hands at midline,and IV) placed into the infant’s hands. Each step lasted about 30 sec. This test wascompleted once on each lab and home visit. During home visits, a reaching tray as depictedin steps I–III was used.

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Figure 3.Results of the reaching assessment in the live context for a) Step I – Looking duration toexperimenter; b) combined Steps II and III – Reaching and grasping behavior; and c) StepIV – Separate looking at toy episodes. Longitudinal patterns are reported from the first labvisit (Lab 1), over up to 4 home visits (Home 1–4), and the second lab visit (Lab 2).Significant differences (p < .05) between the AT and PT group are indicated with a *,differences between AT and untrained 3-month-old infants (NT3) with a †, and significantwithin-group differences for the AT group (lab visit 1 vs. lab visit 2) are indicated with a #.Error bars represent SEM.

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Figure 4.Number of face-toy gaze shifts in the televised context. Untrained 3-month-old infantsshowed the least number of gaze shifts, untrained 5-month-old infants showed the highestnumber of gaze shifts. Both AT and PT groups fell in-between the younger and olderuntrained infants and showed similar amounts of gaze shifting. Error bars represent SEM. *p < .05.

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Tabl

e 1

Gro

upn

#FR

ace

Age

1st

lab

visi

tT

rain

ing

dura

tion

(min

.)#o

f hom

e vi

sits

Age

2nd

lab

visi

tPa

rent

Edu

.B

irth

wei

ght

AT

189

15C

, 1A

, 2M

10.9

0 (1

.75)

125

(23.

70)

3.80

(0.3

8)12

.92

(1.7

7)9.

38 (2

.99)

3621

(578

)

PT18

1014

C, 1

B, 1

A, 2

M10

.90

(1.5

2)14

4 (2

3.70

)3.

80 (0

.331

)12

.93

(1.5

5)9.

94 (2

.24)

3544

(470

)

NT

319

817

C, 1

B, 1

M--

----

12.6

1 (2

.17)

10.0

5 (1

.61)

3280

(377

)

NT

523

1118

C, 2

B, 1

A, 2

M--

----

19.7

0 (1

.93)

9.60

(1.3

0)34

18 (5

15)

Not

e: T

he to

tal n

umbe

r of p

artic

ipan

ts in

eac

h gr

oup

(n) a

nd th

e nu

mbe

r of f

emal

es p

er g

roup

(#F)

are

indi

cate

d. A

ll ot

her v

alue

s are

gro

up a

vera

ges w

ith st

anda

rd d

evia

tions

giv

en in

par

enth

eses

. Age

isre

porte

d in

wee

ks, b

irth

wei

ght i

n gr

am, t

rain

ing

dura

tion

in m

inut

es. P

aren

ts’ e

duca

tion

leve

l was

ass

esse

d on

a sc

ale

from

0 (n

o H

igh

Scho

ol d

egre

e) to

6 (P

ost-d

octo

ral T

rain

ing)

for e

ach

pare

nt a

ndsu

mm

ed (m

ax. 1

2). R

ace

abbr

evia

tions

: C =

Cau

casi

an, B

= B

lack

or A

fric

an A

mer

ican

, A =

Asi

an, M

= M

ore

than

one

race

.

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Table 2

Measure Group

Context

Live passive Live active TV passive

Face

AT 3.23 (6.41) 25.69 (23.76) 48.11 (19.92)

PT 19.26 (27.97) 25.61 (31.03) 44.23 (18.76)

NT3 8.97 (11.55) 21.50 (21.55) 37.69 (17.27)

Toy

AT 69.89 (25.75) 45.54 (36.10) 14.37 (10.05)

PT 59.63 (35.45) 53.54 (40.71) 16.43 (9.52)

NT3 70.85 (23.44) 38.17 (32.05) 17.41 (13.62)

Note: Average looking duration for all groups are reported as proportion of total looking time with standard deviations given in parentheses.

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