Beyond the information given: Infants’ transfer of actions learned through imitation

Journal of Experimental Child Psychology 106 (2010) 62–81

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Beyond the information given: Infants’ transfer of actions learned through imitation Dahe Yang, Jason Sidman, Emily W. Bushnell * Department of Psychology, Tufts University, Medford, MA 02155, USA

a r t i c l e

i n f o

Article history: Received 18 August 2009 Revised 12 December 2009 Available online 8 February 2010 Keywords: Transfer Imitation Action affordances Infant learning Innovation Means-ends behavior Goal-directed behavior

a b s t r a c t Five experiments were conducted to investigate infants’ ability to transfer actions learned via imitation to new objects and to examine what components of the original context are critical to such transfer. Infants of 15 months observed an experimenter perform an action with one or two toys and then were offered a novel toy that was not demonstrated for them. In all experiments, infants performed target actions with the novel toy more frequently than infants who were offered the same toy but had seen no prior demonstrations. Infants exhibited transfer even when the specific part to be manipulated looked different across the toys, even when they had not performed the actions with the demonstration toys themselves, even when the actions produced no effects on the demonstrations, and even when the actions were demonstrated with only a single exemplar toy. Transfer was especially robust when infants not only observed but also practiced the target actions on the demonstration trials. Learning action affordances (‘‘means”) seems to be a central aspect of human imitation, and the propensity to apply these learned action affordances in new object contexts may be an important basis for technological innovation and invention. Ó 2010 Elsevier Inc. All rights reserved.

Introduction The capacity to learn by observing and reproducing the behavior of others is widely recognized as a safe and efficient way to acquire new skills. Furthermore, such imitation is extremely useful for perpetuating skills within a group because it allows even the most unknowledgeable and uninventive * Corresponding author. E-mail address: [email protected] (E.W. Bushnell). 0022-0965/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.jecp.2009.12.005

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members to acquire new strategies (Tomasello, 1999). In line with these conceived advantages of imitation, research has established that even preverbal infants readily learn new behaviors through observing and reproducing others’ actions. Meltzoff (1988b) and Herbert, Gross, and Hayne (2006) found that 9-month-olds imitate simple goal-directed actions such as pressing and pulling with novel objects, and by their second year infants also imitate multistep activities (Bauer & Hertsgaard, 1993; Herbert & Hayne, 2000), tool-using strategies (Bushnell & Boudreau, 1998; Chen & Siegler, 2000), and even inefficient actions (Nagell, Olguin, & Tomasello, 1993; Nielsen, 2006) or highly unusual actions (Meltzoff, 1988a). As prevalent and useful as it is, the full value of imitation lies in how the acquired skills may be extended to new situations. Although learning might be efficient, it would be highly constrained and technology would remain stagnant if individuals learning through imitation were limited to acting with just the one object initially demonstrated and to only the original context. Instead, human learners ‘‘transfer” imitated behaviors to other similar objects and to analogous situations, and they even improve, extend, and expand on the goal-directed actions of others; as the saying goes, people ‘‘build better mousetraps.” Such innovation involves more than just the capacity to imitate; it also requires the recognition of some commonality among distinct exemplars and the ability to diverge from the specifics of the original instance. As such, transfer from imitation may be a later development or a more fragile process than imitation itself. Previous literature supports the idea that transfer from imitation imposes a greater cognitive load than imitation alone. Bauer and Dow (1994) and Barnat, Klein, and Meltzoff (1996) found that 16-month-olds and 14-month-olds, respectively, performed actions they had observed earlier with perceptually different objects less robustly than they performed the actions with the precise objects they had seen manipulated originally. Hayne, MacDonald, and Barr (1997) specifically varied the difference between the original and subsequent objects in a generalization design. They found that 12month-olds exhibited generalized imitation when the second object differed from the first object in color only but not when the objects differed in form or in both color and form. Older infants did show generalized imitation across simple form changes but not across more drastic ones. These results suggest that, at least during infancy, generalizing imitation is highly dependent on the degree of similarity between the initial and subsequent object contexts. Other research suggests that transfer is also sensitive to the delay between the model and the infant’s opportunity to imitate (Hayne et al., 1997), to verbal cueing accompanying the demonstration (Herbert & Hayne, 2000), and to whether or not the infant acted or just observed with the initial objects (Hayne, Barr, & Herbert, 2003). Overall, infants’ generalization from imitation seems to be a volatile phenomenon whose boundaries are unclear and shift not only with infants’ age but also in response to other parameters. Moreover, when transfer from imitation does occur, the question of what the basis for the transfer is arises. Has the child recognized that the new object affords the same action as before, or does the child see that it may yield the same effect as before? For example, in Hayne’s puppet paradigm, infants observe an experimenter remove a puppet’s mitten and shake it to ring a bell hidden inside. They are then given a different puppet to play with. If infants generalize imitation and perform the actions with the second puppet, did they learn from the demonstration to remove puppets’ mittens and shake them or did they learn that puppets have bells inside of them? This contrast for generalization is akin to a recent debate regarding whether imitation itself is based on attention to the model’s means or to the ends achieved by them (cf. Want & Harris, 2002). Some researchers maintain that human infants attend especially to the behaviors demonstrated by a model, suggesting that this focus may subserve social purposes (Call & Carpenter, 2009; Nagell et al., 1993; Nielsen, Simcock, & Jenkins, 2008; Tomasello, Savage-Rumbaugh, & Kruger, 1993). Others have shown that infants can successfully reproduce effects they observe even when they have not witnessed the means for achieving them (Huang & Charman, 2005; Huang, Heyes, & Charman, 2002). A compromise stance is that infants are opportunistic imitators and can focus either on the model’s means or on the ends achieved as circumstances warrant (Bauer & Kleinknecht, 2002; Brugger, Lariviere, Mumme, & Bushnell, 2007; Whiten, McGuigan, Marshall-Pescini, & Hopper, 2009). In the research reported here, we examined infants’ ability to generalize from imitation in light of the means/ends distinction highlighted in the imitation literature. In particular, we investigated whether infants can ‘‘transfer the means,” that is, whether they can learn an effective action by imi-

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tation in one context and then apply their knowledge in another context to achieve a different end. The capacity to employ a common means to serve a variety of functions is an important component of human innovation and technology; consider, for example, the wide array of uses for classic tools such as screws, levers, and pulleys. The origins of this kind of inventiveness during infancy have not yet been explored; in all of the prior research on generalization from imitation, the novel objects subsequently offered to infants yielded the same effect as the object initially demonstrated. Indeed, some research on early social learning suggests that means are tightly linked to specific ends for infants. Elsner and Aschersleben (2003) found that 15- and 18-month-olds’ reproduction of an action was reduced when it led to an effect different from the initially observed one, and Barrett, Davis, and Needham (2007) found that 12- to 18-month-olds had difficulty in learning to use a familiar object for a purpose different from the usual one. In our research, infants explicitly learned through imitation that a common action might lead to different effects with different objects during a training phase. They were then offered a novel object with no demonstration, and whether they reproduced the target action was observed. The results of Experiment 1 established that infants are indeed able to transfer the means under these circumstances. This phenomenon was then examined in further detail in several follow-up studies. Experiment 1 Method Participants A total of 24 14- to 16-month-olds (14 boys and 10 girls, mean age = 15 months 7 days, SD = 18.1 days) participated in Experiment 1. An additional 9 infants were also tested but not included in the final sample because of experimenter error or toy malfunction (n = 4), because they did not imitate the target action on at least one demonstration trial (n = 4), or because the test toy was similar to one they had at home (n = 1). A control group of 24 infants (10 boys and 14 girls, mean age = 15 months 3 days, SD = 14.6 days) was also constituted, with each control infant matched to an experimental infant according to the specific toy presented on the baseline (control infant) and test (experimental infant) trials. Approximately half (n = 11) of the control infants also served as experimental infants but with toys from the alternative sets used in these two roles. The remaining control infants were infants whose test trial was not usable but whose baseline trial was usable, and their baseline toy matched the test toy of a given experimental infant. Infants were recruited from the local community by mail solicitations, and their ethnic distribution reflected the local community’s demographics. Setting All testing was done in a psychology laboratory at Tufts University. The parent, child, and experimenter sat around a 45  90-cm table, with the experimenter and parent opposite each other at the short ends and the baby in a booster seat fastened to one of the table’s long sides. A video camera was positioned opposite the infant and hidden behind a partition. An assistant operated the camera and brought the toys out to the experimenter from behind the partition. Stimulus toys Two sets of cause–effect toys were used as stimuli for Experiment 1. All of the toys had a distinct knob that, when manipulated properly (the ‘‘means”), led to an interesting visual and/or auditory effect (the ‘‘ends”). Except for the manipulandum they shared, the toys within each set were different from one another in size, color, shape, and the number and location of distinct parts. In contrast to the stimuli in prior studies of transfer from imitation, the toys also produced different effects when activated. One set of toys, the ‘‘press” toys, consisted of three objects each with a blue knob protruding from the top of the toy. The knob moved in a downward direction when force was applied from above; this pressing action activated each toy in this set. One of these toys was a commercially available spinning

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toy modified to include the blue knob. When the knob was pressed, the floor of the toy spun around and colorful balls encased within the toy tumbled around. A second toy was a battery-operated stuffed dog fastened to a 30  10-cm board with the blue knob also on the board to the dog’s right. When the knob was pressed, the dog barked and wagged its tail. The third toy was a commercially available Cookie Monster figure in a small plastic frame modified to include the blue knob. When the knob was pressed, the Cookie Monster moved and sang a short song. The three press toys are depicted on the left of the top panel in Fig. 1. The second set of toys, the ‘‘pull” toys, consisted of three toys each with a white oval knob protruding from the front of the toy. The knob moved when it was pulled outward from the toy; this pulling action activated each toy in this set. One of these toys was custom-made and consisted of a small rubber frog at the tip of a rod extending up from a 30  10-m wooden base. The white knob protruded from the front of the base, and when it was pulled, the frog swung in an arc. A second toy was a small colorful can enclosed in a clear Plexiglas box (16  20  12 cm) with the knob protruding from the front. When the knob was pulled, the can inverted and produced a mooing sound. The third toy

Fig. 1. Pressing and pulling sets of toys used in each of the five studies. See text for details. (For interpretation of the references to color in the text descriptions of the toys in this figure, the reader is referred to the Web version of this article.)

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was a custom-made jack-in-the box type of toy composed of a stuffed bunny hidden in a pink Plexiglas cylinder (16 cm tall and 16 cm in diameter) with a lid. The white knob protruded from the front of the cylinder, and when it was pulled, the lid lifted and the bunny popped up and said ‘‘yahoo.” The three pull toys are depicted on the right of the top panel in Fig. 1. Design Infants were assigned to either the ‘‘pull” group or the ‘‘press” group (n = 12 per group), corresponding to the toys with which they were to be tested. Each infant participated in a series of six trials: two warm-up trials, a baseline trial, two demonstration trials, and a test trial.1 Infants in the pull group were presented with one of the press toys on the baseline trial; this toy was not demonstrated but was simply given to the infant to explore. On the demonstration trials, the experimenter showed the infant how to work first one of the pull toys and then another one of them. The infant was given a turn with each toy after the experimenter’s demonstration. Finally, on the test trial, the third toy from the set of pull toys was given to the infant to explore; as on the baseline trial, the toy was not demonstrated. Infants in the press group were presented with an analogous series of trials, but their baseline trial involved one of the pull toys and their demonstration and test trials involved the press toys. Which toy was used on each trial was counterbalanced across infants so that the three toys from each set served equally often on the baseline, demonstration, and test trials. Infants’ experience with a particular toy on the baseline trial was identical to that of other infants with the same toy on the test trial; in both cases, infants were given a toy they had not seen before and it was not demonstrated for them. However, when the toy was given on the test trial, infants had already seen and practiced the appropriate action with other toys on the demonstration trials; the question of interest was whether infants would transfer what they had learned from the demonstrations to the novel test toy. The baseline trials provided an index of how likely infants were to discover or engage in the appropriate action spontaneously, that is, without the benefit of having imitated it with other toys. Hence, the critical comparison in Experiment 1 was between behavior on the baseline trials and behavior on the test trials with the same toy. The baseline trials of infants in the pull group served as the control to which the test trials of infants in the press group were compared and vice versa. Procedure After introductions and informed consent materials were completed, the parent and infant were led into the testing room and seated at a table. Parents were asked to remain supportive but quiet and nondirective throughout the procedure. Two warm-up trials were initially conducted to familiarize the infant with receiving toys from the experimenter and to establish the infant’s comfort with touching the toys. On each warm-up trial, an assistant placed a toy in front of the experimenter, who commented on it enthusiastically and then placed it in front of the child. The child was allowed to explore the toy freely for approximately 60 s, and then the assistant took it away while simultaneously placing the toy for the next trial in front of the experimenter. The warm-up toys were a clear cylinder with beads inside and a pair of colorful blocks. These afforded behaviors such as shaking, banging, and rotating, but they did not have movable parts like the knobs on the stimulus toys and manipulating them did not yield any special effects. After the infant had explored the second warm-up toy, the assistant removed it and placed the stimulus toy designated for the infant’s baseline trial in front of the experimenter. The experimenter commented on the baseline toy and then offered it to the infant to explore; she did not demonstrate how to work the baseline toy or even touch the activating knob. The child was given 30 s to freely explore the baseline toy, and then the assistant removed it and placed the first demonstration toy in front of the experimenter. The experimenter commented on the demonstration toy as she had for all the prior toys and then demonstrated it for the child. The demonstration consisted of two complete activations of the toy out of the child’s reach. The toy was then given to the infant to explore freely for approximately 30 s, after which the experimenter took the toy back, demonstrated the appropriate ac1 Some infants in Experiment 1 and in subsequent studies were given an additional baseline trial following the test trial. This variation and results pertaining to it are discussed in the Additional Data section after all five individual experiments are reported.

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tion two more times, and then gave the toy back to the child for another 30 s. After the child’s second turn, the assistant removed the first demonstration toy and brought out the second one, and the same two cycles of experimenter demonstrations and infant turns was given with this toy. Finally, the assistant removed the second demonstration toy and brought out the toy designated for the infant’s test trial, which was administered just like the baseline trial. That is, the experimenter commented on the test toy and then offered it to the child to explore freely for 30 s, but she did not demonstrate how to work the toy or even touch the activating knob. After the test trial, the parent and infant were given an appreciation gift and escorted from the lab. Scoring The video records of infants’ behavior on the baseline, demonstration, and test trials were scored for several target behaviors, including touching the toy in general, touching the activating knob in particular, and actually generating the toy’s effect. These behaviors were scored on a second-by-second timeline representing the 30-s trial, so that in addition to their presence or absence, approximations of each behavior’s duration were also available. Scoring was done by two student assistants; one watched the video and identified behaviors as she saw them, and the other recorded these behaviors in the appropriate time slots. Infants were included in the final sample only if they generated the effect on at least one demonstration trial and touched the toy on the test trial for at least 3 s. Similarly, baseline trials were used in the control group only if the infant touched the toy for at least 3 s. These criteria were imposed to ensure that the infants were willing and able to interact with the toys. The 3-s cutoff represented the minimum time touching the toy by infants who generated the effect; thus, it was possible to activate the toy with just 3 s of touching it. The videotapes of 7 infants (30% of the sample) were reviewed independently by another team of scorers to assess reliability for scoring the target behaviors. The two scoring teams were considered to agree about the presence/absence of a given behavior if they both recorded it for the trial in question and, furthermore, recorded it within 1 s of each other on the timeline. Across the 28 trials that were scored twice, the two scoring teams agreed in 100% of the instances regarding touching the toy, touching the knob, and generating the effect. Results The numbers of infants who successfully generated the effect or not on the baseline and test trials for each set of toys are shown in the top panel of Table 1. As can be seen, vastly more infants activated

Table 1 Numbers of infants performing the target actions or not on the baseline and test trials in each of the experiments. Press toys

Pull toys

Overall

Yes

No

Yes

No

Yes

No

Experiment 1 Baseline Test

2 12

10 0

0 10

12 2

2 22

22 2

Experiment 2 Baseline Test

3 11

12 4

3 7

12 8

6 18

24 12

Experiment 3 Baseline Test

5 9

7 3

1 8

11 4

6 17

18 7

Experiment 4 Baseline Test

3 9

9 3

5 11

7 1

8 20

16 4

Experiment 5 Baseline Test

3 10

9 2

1 7

11 5

4 17

20 7

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the toy on the test trial than on the baseline trial. Preliminary analyses showed that performance with the press toys did not differ from that with the pull toys in this experiment or any of the subsequent experiments, so the data were collapsed across the two action categories in all analyses further reported. To statistically compare infants’ behavior on the baseline and test trials, a sign test was conducted on the matched pairs of infants who were given the same toy. Infants performed the target action and activated the toys significantly more frequently on the test trial than their matched controls did on the baseline trial (two-tailed binomial p < .001). In considering the test versus baseline trial comparison, it is important to note that infants interacted with the toy enthusiastically on the baseline trial. In fact, infants interacted with the toy overall for as much time on the baseline trial (M = 19.2 s, SD = 1.4) as on the test trial (M = 21.7 s, SD = 1.6), t(46) = 1.132, p = .263. Furthermore, infants also touched the knob in particular for as much time on the baseline trial (M = 9.2 s, SD = 1.3) as on the test trial (M = 6.7 s, SD = 1.4), t(46) = 1.364, p = .179. However, despite their equivalent activity with the toy and their equivalent attraction to the knob in particular, infants in the control group rarely discovered how to manipulate the knob effectively on their own. Discussion The results corroborate many other reports that infants readily learn goal-directed behaviors through imitation (cf. Barr, Dowden, & Hayne, 1996; Bauer & Hertsgaard, 1993; Chen & Siegler, 2000; Meltzoff, 1985; Meltzoff, 1988b). Although infants who were given the toys to explore spontaneously rarely executed the target actions, infants almost always did so after seeing the experimenter perform the actions on the demonstration trials. In comparison with trial-and-error exploration, imitation is a powerful and efficient learning mechanism. What’s more, the results indicate that imitation is also a generative learning mechanism. After imitating the model on the demonstration trials, infants almost always executed the target actions on the test trial with a new toy that had not been demonstrated. These results support prior reports that infants generalize modeled behaviors to objects different in size and color from the demonstration objects (Barnat et al., 1996; Hayne et al., 1997). The results also extend prior results in that the test toy here was different from the learning toys not only in color and size but also in shape and even with regard to the effect it yielded. Only the manipulandum and the action required to operate it were similar across the several toys. On the test trial, infants must have recognized the relevant object part in the context of an otherwise wholly new object and then reapplied the action affordance they knew for it from the prior trials. We have dubbed this process ‘‘transfer of the means” to emphasize that attention to the effective object part and knowledge of its action affordance is what seems to be carried over from the learning trials to the novel toy. It is important to note that the process of transfer from observational learning (as on our test trials) is more demanding in comparison with straightforward imitation with the identical object (as on our demonstration trials). For example, Hayne and colleagues have shown that infants are unable to generalize target actions to novel stimuli at certain ages and across particular delays, whereas they do reproduce the actions on the initial object shown to them at those same ages and across the same delays (Hayne et al., 1997; Hayne et al., 2003; Herbert & Hayne, 2000; Morgan & Hayne, 2005). Similarly, although chimpanzees, orangutans, and even some nonprimate mammals and birds may learn goaldirected behaviors through observational learning (cf. Byrne, 1999; Custance, Whiten, & Bard, 1995; Heyes, Jaldow, Nokes, & Dawson, 1994; Heyes & Saggerson, 2002; Russon & Galdikas, 1993; Whiten & Ham, 1992), only enculturated chimpanzees have been reported to generalize demonstrated actions to novel objects (Bjorklund, Yunger, Bering, & Ragan, 2002). As a clear case in point, Yunger and Bjorklund (2004) found that two enculturated orangutans exhibited deferred imitation but showed no evidence for generalization of imitation. Transfer from observational learning involves more than straightforward imitation in another sense as well, and that is with regard to the scope of the knowledge acquired. When individuals learn a goal-directed behavior by imitation, they have learned something useful to be sure; however, without transfer, the new knowledge can be (re)applied in only very limited circumstances, namely with just the same kind of object as was demonstrated in the first place. But with transfer, the learned behavior may be applied to a wide range of other objects, indeed to anything that affords acting on

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in that way. For instance, when infants learn by imitation to pull the knob to make the frog jump, with transfer they are also prompted to pull knobs attached to a variety of other objects. Often this action may be unproductive, but in some instances it may lead to the discovery of unanticipated new effects. Thus, transfer ‘‘guides” the exploration of novel objects and may thereby be integral to innovation; paradoxically, transfer from imitation may serve as the ‘‘roots of invention” (see Bushnell, Sidman, & Brugger, 2006). Given its potential significance and its distinction from straightforward imitation, it is important to further understand the process of transfer in infants and young children. What circumstances promote transfer, and what are its limitations and boundaries? What, more precisely, is learned during the demonstrations and then carried over to the new toy? In Experiment 1, infants’ transfer seems to have been facilitated by attention to the manipulandum and knowledge of its action affordance. Attention to the manipulandum alone (‘‘stimulus enhancement”) was probably insufficient to support transfer given that infants focused on the knobs just as much on the baseline trial as on the test trial yet rarely succeeded in activating the toys. Thus, familiarity with the target action was also important to the transfer observed. However, familiarity with the action can be decomposed into two distinct aspects. First, there is the perceptual/spatial nature of the action; in the case of pressing, for example, infants see the knob moving downward relative to the top of the object. Developmental research has established that infants are visually sensitive to such object-relative movement patterns (Kellman & Spelke, 1983; von Hofsten & Spelke, 1985) and motion trajectories (Arterberry & Yonas, 1988; Gibson, Owsley, & Johnston, 1978; Gredeback & von Hofsten, 2004). Thus, the perceptual information available during the demonstration trials may have supported transfer by showing infants what part of the test object to reach for and what sort of motion path to recreate with it. Conversely, there is also a motoric/kinesthetic aspect of the action provided by the demonstrations. While imitating the experimenter on these trials, infants generate and internally experience certain muscular forces exerted at particular angles, distances, and rhythms. Repeating these movements on the demonstration trials may lead to ‘‘muscle memory” for them, generating a so-called ‘‘motor attractor” (cf. Diedrich, Thelen, Smith, & Corbetta, 2000; Thelen, Schoner, Scheier, & Smith, 2001). Thus, when presented with the test toy, infants could have been ‘‘primed” to execute the same motor pattern. To further investigate these distinct aspects of the action component that may be learned by imitation and support subsequent transfer, we conducted another experiment following the general paradigm of Experiment 1. In Experiment 2, infants observed the experimenter activate two different toys on the demonstration trials as before, but they were not given a turn to imitate the experimenter. Thus, when presented with the novel toy on the test trial, infants had seen the pressing or pulling action directed to the knob on other toys, but they had not practiced these actions themselves. Infants’ performance on the test trial compared with that on the baseline trials and compared with the results of Experiment 1 may clarify the relative roles of perceptual and motor representations as they support transfer from imitation. Experiment 2 Method Participants A total of 30 14- to 16-month-olds (21 boys and 9 girls, mean age = 14 months 29 days, SD = 19.5 days) participated in Experiment 2. An additional 6 infants were also tested but not included in the final sample because of experimenter error or parental interference (n = 2), because they were uncooperative or wary (n = 3), or because the test toy was similar to one they had at home (n = 1). A control group of 30 infants (18 boys and 12 girls, mean age = 15 months 3 days, SD = 18.7 days) was also constituted as in Experiment 1, with each control infant matched to an experimental infant according to the toy presented on the baseline (control infant) and test (experimental infant) trials. Of the 30 control infants, 19 also served as experimental infants but with toys from the alternative sets used in these two roles. The remaining control infants were infants whose test trial was not usable but whose baseline trial was usable, and their baseline toy matched the test

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toy of a given experimental infant. Infants were recruited in the same way and from the same population as for Experiment 1. Setting, design, procedure, and scoring The setting, overall design, general procedure and scoring scheme were identical to those for Experiment 1 except that in Experiment 2 infants were not given a turn to imitate the experimenter’s actions on the demonstration trials. Infants were presented with two warm-up trials and a baseline trial involving a toy from the alternative action set as described earlier. Then the first toy from the target action set was given to the experimenter, who solicited the infant’s attention and activated the toy twice. The experimenter then paused, commented on the toy generically, and allowed the infant to look at but not touch the toy for a brief period. This pause and filler conversation substituted for the turn infants had with the demonstration toy in Experiment 1. After the pause, the experimenter solicited the infant’s attention again and activated the toy twice more. Then the second toy from the target action set was brought out and demonstrated in the same way, again without turns for the infant to imitate. Finally, the toy designated for the infant’s test trial was brought out and offered to the infant with no demonstration. The infant was permitted to explore the test toy freely for approximately 30 s. Stimulus toys As in Experiment 1, three toys activated by pressing and three others activated by pulling were used in Experiment 2. The press toys used were the same as in Experiment 1—the spinning balls, dog, and Cookie Monster toys. The pull toys consisted of the same frog and mooing toys as in Experiment 1 and a new toy developed to replace the bunny toy that was in repair at the time. The mooing toy was slightly altered in that it was covered with opaque material to soften the corners and prevent infants from trying to access the sounding can directly. The new gopher toy was very similar to the bunny toy; it was composed of a battery-operated plastic gopher hidden in a purple cylinder (11 cm tall and 18 cm in diameter) with a clear dome at the top. The pull knob protruded from an ovoid base attached to the cylinder, and when the knob was pulled, the gopher rose up into view through the dome accompanied by a whirring noise. The pull toys in Experiment 2 each had a spherical yellow knob protruding outward from the toy; this knob replaced the white ceramic knob used in Experiment 1 because some infants had trouble gripping the ceramic knob. All of the toys used in Experiment 2 are depicted in the second panel in Fig. 1. Results The numbers of infants who successfully generated the effect or not on the baseline and test trials in Experiment 2 are shown in the second panel of Table 1. Two things are immediately apparent from the data. First, as in Experiment 1, more infants activated the toys on the test trial than on the baseline trial. A sign test conducted on the matched pairs of infants who were given the same toy showed that infants performed the target action and activated the toys significantly more frequently on the test trial than their matched controls did on the baseline trial (two-tailed binomial p < .005). In considering this comparison, it is again important to note that on the baseline trial, infants were motivated and willing to interact with the toy. Infants in Experiment 2 interacted with the toy overall for as much time on the baseline trial (M = 19.9 s, SD = 1.3) as on the test trial (M = 21.3 s, SD = 1.3), t(58) = 0.762, p = .449, and they also touched the knob in particular for as much time on the baseline trial (M = 9.0 s, SD = 1.3) as on the test trial (M = 10.8 s, SD = 1.5), t(58) = 0.900, p = .372. The control infants’ failure to activate the toy despite interest in it coupled with the success of infants on the test trial indicates the importance of merely observing the model. However, the second result notable in Table 1 is that infants in Experiment 2 did not activate the toy as consistently as infants in Experiment 1. Whereas 60% of the infants in Experiment 2 activated the toy on the test trial, more than 90% of the infants in Experiment 1 did so. Because the toys and most aspects of the procedure were similar in Experiments 1 and 2, we directly compared the test trial performance of infants in the two experiments. Infants in Experiment 2 were significantly less successful at activating the toys than infants in Experiment 1, v2 = 6.96, two-tailed p < .01. Thus, merely

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observing the model on the demonstration trials does facilitate pressing and pulling the knobs on the novel test toy, but it is not as effective as observing the model and also practicing the actions prior to the test trial.2 Discussion The results of Experiment 2 indicate that both perceptual and motor representations derived from prior imitation contribute to transferring an action to a novel object. Infants who merely observed the experimenter perform an action with two toys nevertheless performed this action on a novel toy more frequently than infants who had not seen any demonstrations. These results are consistent with those of Barnat and colleagues (1996), who found that 14-month-olds who only observed a model act on some toys later acted similarly on enlarged and differently colored versions of the toys. Both the results of Experiment 2 and those of Barnat and colleagues seemingly conflict with Hayne and colleagues’ (2003) report that infants who did not practice actions themselves failed to exhibit transfer. However, the task demands in Hayne and colleagues’ research were arguably greater than in Experiment 2 given that three action steps were involved in the demonstrated events and the novel test toys were offered after a 24-h delay. The results of Experiment 2 make it clear that, at least with simple one-step behaviors and minimal delays, merely observing an effective action is sufficient to support transfer to a novel object. Infants could see from the demonstrations that the object’s knob is the part to act on, and they could see the trajectory through which it moved. They were evidently able to recruit this perceptual knowledge to generate their own effective actions for the first time with the novel test toy. However, the results of Experiment 2 also indicate that motor practice supports transfer above and beyond the utility of perceptual knowledge alone. Infants in Experiment 2 who merely observed the experimenter act on the demonstration trials did not activate the test toy as frequently as infants in Experiment 1 who observed and also imitated the model’s action prior to the test trial. This crossstudy result is consistent with Hayne and colleagues’ (2003) finding that motor practice facilitates generalization (and indeed is necessary for it in their paradigm). Those authors suggested that practice facilitates transfer more than just observing because it generates a richer multimodal memory representation that is, therefore, more retrievable. We would also emphasize a more proactive account based on the concept of motor priming. Infants who imitated the experimenter’s action on the demonstration trials would have formed a procedural memory or ‘‘motor attractor” for the action. This representation would include parameters of the action not easily seen in another’s demonstration such as the amplitude and direction of force required to move the toy’s knob. Infants who had only observed the action would need to discover these parameters with the test toy, whereas infants who had practiced the actions before would have worked them out already. Thus, they are effectively ‘‘primed” to execute the same motor pattern when given the test toy, and this may underlie their robust transfer. Motor practice may support transfer in some more indirect ways as well. For example, with one’s own movement on the demonstration (imitation) trials, the action’s causal nature may be more apparent. When infants just see the experimenter’s hand moving and parts of the toy moving or sounding accordingly, they essentially observe a correlation. However, when they are acting themselves, babies can slow their hands’ movement and see that the toy’s movement slows, they can press the knob again and hear that the sound repeats, and so on. Thus, with motor practice, infants may get a stronger sense of agency and, therefore, more readily transfer the action to a new toy expecting to generate an effect. Overall, the results of Experiment 2 are consistent with those of Experiment 1 in establishing that from observational learning, infants gain knowledge that goes beyond the information given in the specific learning context. After watching an experimenter perform an action on two demonstration 2 We subsequently ran another study also very similar to Experiment 1 except that in place of the infant’s turn on the demonstration trials, the experimenter commented on and labeled the action with a nonsense word. This variation was designed to increase the infant’s attention to the action. However, the labeling manipulation had no effect. Hence, this experiment amounted to a replication of Experiment 2, and indeed the results were quite similar to those for Experiment 2; on the baseline trial, 6 infants generated the effect and 18 did not, and on the test trial, 14 infants generated the effect and 10 did not.

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objects (Experiment 2) and especially after also acting on those toys themselves (Experiment 1), infants systematically applied the same action to a novel toy. We think that this transfer depends on attending to the effective object part and learning its action affordance during the demonstrations. Infants then recognize the same part and apply the action accordingly in a new context on the test trial. Such transfer of the means is significant for the generativity and innovation it can engender. It might be argued that the transfer shown in Experiments 1 and 2 was to be expected because although the training and test toys were different overall, the object parts that activated them (i.e., the knobs for pressing or pulling) were identical. Thus, infants may simply have learned a specific response to a stimulus that was constant across objects, for example, to press the blue button. It is still noteworthy that infants were able to abstract this constant part from the diverse objects carrying it; that is, their stimulus–response knowledge was not context bound and, thus, can serve the generative function we have emphasized. Nevertheless, the question arises as to how broad the transfer process is for infants. We investigated this issue in a third experiment employing the same transfer paradigm, but this time with the stimulus toys also varying with respect to the parts that activated them. Thus, in Experiment 3, the manipulanda of the several toys presented to each infant were different in color, shape, composite material, and their position on the objects. The purpose of Experiment 3 was to further establish the transfer phenomenon observed in the prior studies and to investigate whether infants are able to transfer from imitation across an even broader range of objects. Experiment 3 Method Participants A total of 24 14- to 16-month-olds (13 boys and 11 girls, mean age = 14 months 21.3 days, SD = 19.1 days) participated in Experiment 3. An additional 6 infants were also tested but not included in the final sample because of experimenter error (n = 1) or because they did not imitate the target action on at least one demonstration trial (n = 5). As for Experiments 1 and 2, a control group of 24 infants (13 boys and 11 girls, mean age = 14 months 23.9 days, SD = 18.8 days) was also constituted, with each control infant matched to an experimental infant according to the specific toy presented on the baseline (control infant) and test (experimental infant) trials. Of the 24 control infants, 14 also served as experimental infants but with toys from the alternative sets used in these two roles. The remaining control infants were infants whose test trial was not usable but whose baseline trial was usable, and their baseline toy matched the test toy of a given experimental infant. Infants were recruited in the same way and from the same population as before. Setting, design, procedure, scoring, and stimulus toys Except for certain aspects of the stimulus toys to be described, the method for Experiment 3 was identical to that for Experiment 1. The key feature of Experiment 3 was that the manipulanda of the several toys presented to each infant (as well as the toys themselves) were different from one another. A set of eight different knobs or handles was created for Experiment 3. For the press toys, these consisted of a green wooden cube, a silver metal faucet handle, a red wooden cylinder, and the blue circular knob used in Experiments 1 and 2. For the pull toys, the knobs consisted of a red 12-sided dice-like object, a blue wooden cylinder, a silver metal D-ring, and a yellow wooden sphere. The toys were modified so that within each set, any given knob could be attached to any one of the toys. The four toys presented to each infant all had different knobs, and the various knobs were used equally often across infants with particular toys and on particular trials. Two of the press toys used in Experiment 3 were the same Cookie Monster and dog toys used in the first two experiments except that for Experiment 3 the knobs were modified as described and the dog was enclosed in Plexiglas (to discourage infants from picking it up). The third press toy was a press version of the mooing toy used as a pull toy in Experiments 1 and 2. The press mooing toy was a small sounding can enclosed in a blue box (17  15  18 cm) with an L-shaped shaft for the knob protruding from the front. When the knob was pressed down, the can inverted and produced a mooing sound. The

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press mooing toy was developed to replace the spinning balls toy because several infants in the prior studies had a similar toy at home and needed to be eliminated from the sample. The pull toys for Experiment 3 were the same toys used for Experiment 1—the frog, pull mooing, and bunny toys—except that for Experiment 3 the knobs were modified as described and the mooing toy’s casing was opaque as for Experiment 2. All of the toys used in Experiment 3 are shown in the third panel of Fig. 1, which also shows an assortment of the different knobs used. Results The numbers of infants who successfully generated the effect or not on the baseline and test trials in Experiment 3 are shown in the third panel of Table 1. A sign test conducted on the matched pairs of infants who were given the same toy showed that infants performed the target action and activated the toys significantly more frequently on the test trial than their matched controls did on the baseline trial (two-tailed binomial p < .005). Because the toys and most aspects of the procedure were similar in the two studies, we also directly compared the performance of infants in Experiment 3 with that of infants in Experiment 1. Although the results in general are less robust in Experiment 3, the test trial performance of infants in Experiment 3 was not significantly different from that of infants in Experiment 1 (Fisher exact p = .136).3 In considering the test versus baseline trial comparison, it is again important to note that infants interacted enthusiastically with the toy on the baseline trial. As in the first two experiments, infants in Experiment 3 interacted with the toy overall for as much time on the baseline trial (M = 18.8 s, SD = 1.7) as on the test trial (M = 22.4 s, SD = 1.4), t(46) = 1.661, p = .104, and they also touched the knob in particular for as much time on the baseline trial (M = 10.1 s, SD = 1.3) as on the test trial (M = 12.0 s, SD = 1.4), t(46) = 1.011, p = .317. However, despite this activity with the toy and even with the knobs in particular, most infants in the control group still did not discover how to manipulate the knob to generate the toy’s effect. Discussion As in Experiment 1, infants in Experiment 3 exhibited transfer from the imitative context to a novel toy. After they observed and imitated an experimenter acting on toys in two demonstration trials, infants applied the target action to a novel toy more frequently than infants who had no prior demonstrations. Although successful activation was somewhat diminished in Experiment 3, overall performance was not significantly different from that in Experiment 1. Thus, from the demonstration trials, most infants seemed to learn something more abstract than a simple action response to a particular kind of handle. They learned the appropriate action from imitating the experimenter with the first two toys and extended the action to the third toy despite the fact that the test toy and its activating knob (and also the effect it yielded) were different from the toys and their knobs on the demonstration trials. The breadth of stimuli over which transfer from imitation may occur makes the process all the more valuable as a guide for exploring new objects and a potential source of innovation. Because the toys, their knobs, and their effects all were deliberately varied across the demonstration and test trials in Experiment 3, the only common factor across the trials was the action component, that is, the pressing or pulling movement directed toward a generic appendage on the stimulus toy. This action affordance seems to be what infants learned through observation and practice on the demonstration trials and then carried over to the novel test toy. This interpretation is consistent with an emphasis on attention to the means during infants’ imitation (Call & Carpenter, 2009; Nagell et al., 1993; Nielsen et al., 2008; Tomasello, 1999), and we suggest that it is the means in particular that is transferred when infants go beyond the initial learning context. In Experiments 1 to 3, all of the action affordances that infants observed and practiced led to interesting auditory–visual effects, albeit different ones across the series of toys. Thus, the actions on the knobs were supported and reinforced by an ensuing effect of some sort. What role does this ‘‘causal” 3 The Fisher exact probability test was used as the recommended default to the chi-square test when the expected value for one or more cells was less than 5.

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nature of the actions play in the learning and transfer process? The action component in our paradigm may be attended to, learned, and applied to new objects specifically because of its effectiveness; thus, infants may come to perceive and value the action as a generic ‘‘way to make things happen.” Alternatively, infants may learn the action affordances of the knobs in and of themselves as ‘‘the thing to do” with an appendage protruding from an object; an effect following the action may be unessential. To distinguish between these two accounts for learning and transferring actions, we conducted Experiment 4. New stimuli were developed for the demonstration trials so that infants could observe and practice the target actions prior to the test trial, but during the demonstrations the actions did not lead to any effects. Thus, from the demonstration trials, infants could learn an action affordance for the knobs and develop a motor attractor for the actions, but they would not acquire a sense of agency or be reinforced for performing the actions. The relative importance of these aspects of imitation for subsequent transfer may become clear from the results of Experiment 4 in comparison with those of the prior studies. Experiment 4 Method Participants A total of 24 14- to 16-month-olds (14 boys and 10 girls, mean age = 14 months 26.1 days, SD = 16 days) participated in Experiment 4. An additional 4 infants were also tested but not included in the final sample because they did not imitate the target action on at least one demonstration trial. A control group of 24 infants (14 boys and 10 girls, mean age = 14 months 28.7 days, SD = 15.4 days) was also constituted, with each control infant matched to an experimental infant according to the specific toy presented on the baseline (control infant) and test (experimental infant) trials. Of the 24 control infants, 20 also served as experimental infants but with toys from the alternative sets used in these two roles. The remaining control infants were infants whose test trial was not usable but whose baseline trial was usable, and their baseline toy matched the test toy of a given experimental infant. Infants were recruited in the same way and from the same population as for the prior studies. Setting, design, procedure, scoring, and stimulus toys Except for certain aspects of the stimulus toys to be described, all other aspects of the method for Experiment 4 were identical to those for Experiment 1. As in the previous experiments, two sets of stimuli were used: one involving pressing and the other involving pulling as the target actions. In Experiment 4, infants were presented with a complete toy that could yield an effect only on the baseline and test trials. On the demonstration trials, they were presented with ‘‘detached” versions of the press and pull knobs that could be manipulated as usual, but this manipulation did not lead to any consequent effect. This experimental variation required toys from which the manipulanda could be removed, so some new stimulus materials were developed. One toy adapted for Experiment 4 was the gopher toy described for Experiment 2. Press and pull versions of this were created. In the pull version, a knob protruded out from an ovoid base attached to the front of the cylinder forming the toy’s main body. In the press version, a knob protruded up from a similar ovoid base. For each version, the ovoid base containing the knob and its movement mechanism could be detached from the toy itself. When the knobs were attached to the toy, manipulating them appropriately led to the gopher rising and whirring as described earlier. The second toy developed for Experiment 4 was a new ‘‘spinner” toy. This consisted of a cream-colored Plexiglas cylinder taller (22 cm) and thinner (15 cm in diameter) than that for the gopher toy. The cylinder was opaque and covered with colorful stickers except for the top portion (7 cm), which was plain and transparent. Inside the cylinder and visible through the clear portion was an upright disk. When the activating knob was pressed or pulled, this disk rotated rapidly and colored lights on its rim flashed in a sort of disco ball display. As with the gopher toy, press and pull versions of the spinner toy were created, with the appropriate activating knob projecting from the same kind of detachable base at the bottom of the cylinder. The knob for the press versions of both toys was a small blue cylinder; for the pull versions, it was a yellow sphere.

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Infants were presented with the press version of one of the toys on the baseline trial and with the pull version of the other toy on the test trial or vice versa. The two toys were used equally often on the baseline and test trials, and the press and pull versions of each toy were likewise counterbalanced. The critical manipulation for Experiment 4 involved the objects used for the demonstration trials. These were the ‘‘detached means” from the gopher and spinner toys; the ovoid bases containing the press and pull knobs were removed from the bodies of the toys and presented to infants by themselves. The knobs could be pressed and pulled as usual, and the experimenter modeled this and gave infants a turn to do it on the demonstration trials, but the actions did not lead to any special effect. A blue rectangular cover and also a red mounded cover were made to fit over the ovoid bases so that there were two perceptually different versions of the detached means for the demonstration trials. Thus, an infant assigned to the press action set, for example, would be shown how to press the knob and given a turn to do it with the blue rectangular detached means on one demonstration trial and with the red mounded detached means on the other one. The infant would then be given the complete gopher or spinner toy with the plain ovoid base and press knob attached on the test trial without any demonstration of the toy. The two versions of the detached knobs as well as the gopher and spinner toys used in Experiment 4 are depicted in the fourth panel of Fig. 1. Results The numbers of infants who successfully generated the effect or not on the baseline and test trials in Experiment 4 are shown in the fourth panel of Table 1. These results are similar to those for Experiments 1 and 3; most infants activated the toys on the test trial but not on the baseline trial. A sign test conducted on the matched pairs of infants who were given the same toy showed that infants performed the target action and activated the toys significantly more frequently on the test trial than their matched controls did on the baseline trial (two-tailed binomial p < .005). Although the test toys were necessarily somewhat different from those in the prior studies, we took the liberty of comparing performance in Experiment 4 to that in Experiment 1, where the demonstrated actions led to effects, and also to that in Experiment 2, where the actions likewise led to effects but infants had only observed them. Infants in Experiment 4 activated the test toy more frequently than infants in Experiment 2, v2 = 3.48, p = .06, and just as frequently as infants in Experiment 1 (Fisher’s exact p = .67). It is again important to note that infants interacted enthusiastically with the stimuli on the baseline trial. Infants in Experiment 4 interacted with the toy overall for as much time on the baseline trial (M = 18.9 s, SD = 1.8) as on the test trial (M = 20.7 s, SD = 1.3), t(46) = 0.843, p = .404, and they also touched the knob in particular for as much time on the baseline trial (M = 12.2 s, SD = 1.3) as on the test trial (M = 10.4 s, SD = 1.0), t(46) = 1.132, p = .264. However, this interest in the toys and knobs did not usually lead to discovery of the target actions. Discussion The results of Experiment 4 suggest that the reinforcement or sense of agency that infants may receive from acting to produce an effect is not essential to transferring actions to novel objects. Infants in Experiment 4 readily performed the target actions on the test trial even though neither the experimenter’s prior demonstrations nor the infant’s prior imitations had been followed by interesting effects. Of course, infants may have perceived some alternative ends to their actions in Experiment 4; for example, perhaps simply moving the knobs or matching the experimenter’s behavior on the demonstration trials was reinforcing. However, an effect of the conventional sort—external to the self and consequent to the action—does not seem to be crucial for transferring an action learned by imitation. Infants undoubtedly are intrigued by such effects and find producing them to be satisfying. Nevertheless, the results of Experiment 4 establish that merely knowing that the knobs afford certain movements and practicing these are sufficient for infants to apply the actions to novel objects with similar knobs. The results of Experiment 4 in conjunction with the results of the previous studies support the idea that developing a motor attractor is an important feature of imitation that facilitates transferring actions to new object contexts. Infants who performed the target actions on the demonstration trials

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(e.g., Experiments 1 and 4) exhibited more robust transfer than infants who only observed the actions (Experiment 2). Moreover, infants who only practiced the actions on the demonstration trials (Experiment 4) transferred them just as robustly as infants who both practiced the actions and learned that they produced effects (as in Experiment 1). It seems that having a chance to explore and master the kinematics of an action helps to form a vivid representation that can be easily accessed in the context of a novel object. Before a firm conclusion about the importance of motor practice can be drawn, however, another issue must be addressed. In the transfer paradigm as implemented in Experiments 1 to 4, infants who performed the target actions on the demonstration trials saw the actions both when the experimenter modeled them and when they themselves imitated them, whereas infants who merely observed on the demonstration trials had only approximately half of this exposure to the actions before the test trial. Thus, it is possible that the more robust transfer shown by infants who were given a turn to imitate on the demonstration trials is an effect of additional exposure rather than an effect of motor practice per se. To explore this possibility, a final experiment was conducted using a truncated paradigm. In Experiment 5, infants both observed and imitated the experimenter during the demonstration phase, but this consisted of just one demonstration trial. Thus, their sheer exposure to the target actions was approximately equivalent to that of infants in Experiment 2, who only observed the actions but did so on two demonstration trials, and it was approximately half that of infants in the previous studies permitting motor practice. Experiment 5 Method Participants A total of 24 14- to 16-month-olds (16 girls and 8 boys, mean age = 15 months 5.7 days, SD = 17.0 days) participated in Experiment 5. An additional 6 infants were also tested but not included in the final sample because of experimenter error (n = 2), because of toy malfunction (n = 1), or because they did not imitate the target action on the demonstration trial (n = 3). A control group of 24 infants (16 girls and 8 boys, mean age = 15 months 4.3 days, SD = 19.4 days) was also constituted as in the prior studies. Of the 24 control infants, 21 also served as experimental infants but with toys from the alternative action sets used on their baseline and test trials. The remaining control infants were infants whose test trial was not usable but whose baseline trial was usable, and their baseline toy matched the test toy of a given experimental infant. Infants were recruited in the same way and from the same population as for the prior studies. Setting, design, procedure, and scoring The method for Experiment 5 was identical to that for Experiment 1 except that infants in Experiment 5 had just one demonstration trial. Thus, each infant was presented with a baseline trial with a toy from one action set, a demonstration trial with a toy from the alternative action set, and a test trial with another toy from the action set used on the demonstration trial. As in Experiments 1, 3, and 4, the demonstration trial included both modeling by the experimenter and turns for the infant. However, because infants had just one demonstration trial, they had only half as much exposure to the target action as infants in Experiments 1, 3, and 4 and approximately the same level of exposure as infants in Experiment 2 (who had two demonstration trials but no turns for themselves with the toys). Stimulus toys As in the previous studies, two sets of toys were used in Experiment 5: one involving pressing and the other involving pulling. The press toys were the Cookie Monster toy and the press versions of the gopher and spinner toys described for earlier experiments. The activating knob for all of the press toys was the flat blue knob used in Experiment 1. The pull toys in Experiment 5 were the frog toy and the pull versions of the gopher and spinner toys described for earlier experiments. The activating knob for all of the pull toys was the yellow sphere used in Experiments 2 and 4. All of the toys used in Experiment 5 are depicted

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in the last panel in Fig. 1. Half of the infants were tested with press toys and half with pull toys, and the different toys within each action set were used equally often on the various trials. Results The numbers of infants who successfully generated the effect or not on the baseline and test trials in Experiment 5 are shown in the last panel of Table 1. As in all of the prior experiments, more infants activated the toys on the test trial than on the baseline trial. A sign test conducted on the matched pairs of infants who were given the same toy showed that infants performed the target action and activated the toys significantly more frequently on the test trial than on the baseline trial (two-tailed binomial p < .001). Although the toys differed somewhat, we also compared the performance of infants in Experiment 5 with that of infants in Experiment 2, who had similar exposure to the target actions but did not perform them prior to the test trial. The performance of infants in Experiment 5 did not differ from that of infants in Experiment 2, v2 = 0.69, p = .406. We also compared the performance of infants in Experiment 5 with that of infants in Experiment 1, who practiced the target actions on two demonstration trials and, thus, had twice the exposure to them as in Experiment 5. The performance of infants in Experiment 5 did not differ from that of infants in Experiment 1 (Fisher’s exact p = .13). As in the prior studies, infants interacted with the stimuli enthusiastically on the baseline trial. In Experiment 5, infants touched the toy overall for as much time on the baseline trial (M = 22.0 s, SD = 1.4) as on the test trial (M = 21.6 s, SD = 1.3), t(46) = 0.216, p = .828, and they also touched the knob in particular for as much time on the baseline trial (M = 13.8 s, SD = 1.4) as on the test trial (M = 12.5 s, SD = 1.2), t(46) = 0.661, p = .512. However, this spontaneous activity on the baseline trial did not usually lead to discovering the target action and the toy’s effect. Discussion The results of Experiment 5 are somewhat ambiguous with regard to the relative importance (for transfer) of exposure to an action versus the opportunity to practice it. Infants’ performance on the test trial was in effect midway between that of infants in Experiments 1 and 2 and was not statistically different from either one. Thus, infants’ behavior was similar to that of infants who had the same exposure to the target actions but no motor practice (Experiment 2), suggesting that seeing an action performed additional times may be an adequate substitute for executing it oneself. This interpretation is consistent with the intriguing concept of ‘‘mirror neurons” (see Brass & Heyes, 2005). However, infants’ performance was also similar to that of infants with approximately twice as much exposure to the target actions (Experiment 1), whereas the performance of infants without motor practice differed from this same comparison group. This contrast suggests that motor practice does add something to the equation so far as subsequent transfer is concerned. This interpretation is consistent with the findings of Hayne and colleagues (2003), who found that regardless of the amount of exposure, only infants with motor practice generalized the actions to a new stimulus. The results of Experiment 5 speak more clearly to another issue, namely that of multiple exemplars. In Experiments 1 to 4, infants observed the experimenter demonstrate the target action with two different toys before the test trial. In Experiment 5, however, infants observed the experimenter demonstrate the action to only one toy; thus, they did not see the experimenter model transferring the action to a new toy. Nevertheless, infants in Experiment 5 transferred the action to a new toy themselves, and they did so as readily as infants who had seen demonstrations with different toys. These results indicate that seeing and imitating an action with a single sample object is sufficient to prompt transfer. Although multiple exemplars might conceivably enhance transfer, they are by no means necessary for it. Additional data In each of the experiments reported above, infants performed the target actions more frequently on the test trial than on the baseline trial. These results suggest that infants learned an action affordance from observing and in most cases practicing the action on the demonstration trials and then trans-

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ferred this knowledge to apply the action to a new object on the test trial. However, in Experiments 1 to 5, the baseline trial always preceded the test trial. Such free play with the stimuli prior to demonstrations with them is a conventional control procedure in studies of infant imitation (cf. Bauer & Hertsgaard, 1993; Bauer & Mandler, 1992). Even so, this design feature may raise order effect concerns regarding the results of Experiments 1 to 5. Hypothetically, infants may have been more comfortable or more motivated to interact with the toys on the test trial than on the baseline trial simply because the situation was more familiar and because they knew that the toys could generate effects. This greater comfort and interest may have led infants to frequently ‘‘discover” the target action on the test trial as opposed to actually transferring it from prior learning. Such concerns are greatly alleviated by the fact that in Experiments 1 to 5, infants played with the toys and even touched the activating knobs for as much time on the baseline trials as on the test trials. These results indicate that infants were sufficiently comfortable and well motivated to explore the toys on the baseline trial. They also indicate that the activating knobs were perceptually salient in their own right; that is, the demonstrations were not just useful for enhancing attention to the knobs because that was inherently high anyway. Similarly, the results of Experiment 4 clarify that merely knowing that the toys could produce interesting effects is unlikely to account for infants’ performance. In Experiment 4, infants did not learn that the toys could produce effects on the demonstration trials, yet they applied the target actions on the test trial robustly. These considerations make it unlikely that infants’ success on the test trial relative to the baseline was due only to order effects related to comfort, general motivation, stimulus enhancement, or goal emulation. Observing and in most cases practicing the target action seems to have been an essential contribution of the demonstration trials. Nevertheless, the best way to eliminate any possibility that some kind of order effect accounts for our results would be to administer the baseline trial after the test trial for some infants. Appropriately, it happens that infants in Experiments 1 to 3 were indeed administered a baseline trial after the test trial in addition to the one they experienced beforehand. Like the initial baseline trial, this ‘‘post”-baseline also consisted of the experimenter just offering a toy to the infant without demonstrating it or even touching the activating knob. The toy was from the alternative action set than was used on the infant’s demonstration and test trials, and it was also different from the toy used on the initial baseline trial. Because of these design constraints and the availability of certain toys, not all infants in Experiments 1 to 3 received a post-baseline trial. Nevertheless, across the three experiments, some 49 infants experienced a post-baseline trial, and these involved a variety of toys from both action sets. Of the 49 infants who experienced a baseline trial both before and after the test trial, 14 activated the toy on the initial baseline, 17 did so on the post-baseline, and 28 did so on the test trial (recall that this sample includes infants from Experiment 2 who only observed on the demonstrations). To examine whether infants were more likely to activate the toy on the post-baseline trial than on the initial one (in line with an order effect), a within-participant McNemar change test was conducted. This analysis showed that infants’ behavior did not differ across their initial and post-baseline trials (McNemar two-tailed p = .65). In contrast, a similar analysis showed that infants were more likely to activate the toy on their test trial than on the baseline trial that followed it (McNemar two-tailed p < .05). These results establish that even when they are comfortable with the toys and already know that they can produce interesting effects, infants are not likely to spontaneously discover how to activate them. Infants were only likely to activate a novel toy affording a given action after they had observed and especially after they had also practiced that particular action with other toys. Observing and executing the actions during the demonstration phase clearly facilitated applying them to a novel toy; hence, it is appropriate to characterize the results as evidencing transfer from imitation. General discussion The research reported here was designed to investigate infants’ ability to transfer actions learned via imitation to new objects and to examine what components of the original context are important to such transfer. Overall, the results indicate that by 15 months of age, transfer from imitation is a robust phenomenon. In all five experiments, infants who had seen an experimenter perform an action with one or two toys performed the action with a novel toy more frequently than infants who

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were offered the same novel toy but with no prior demonstrations. This was true despite the fact that the novel toy was perceptually different and yielded a different effect than the demonstrated toys. Moreover, infants transferred target actions to novel toys even when they had only seen but not performed the actions beforehand (Experiment 2), even when the specific part to be manipulated looked different (Experiment 3), even when the demonstrated actions produced no special effects (Experiment 4), and even when the actions were demonstrated with only a single exemplar (Experiment 5). The transfer observed here goes beyond that reported in prior studies in several important respects. First, the demonstration and test toys differed more drastically from one another. In prior research, the toys differed in color and/or size only; they were the same ‘‘kind” of thing (cf. Barnat et al., 1996; Bauer & Dow, 1994; Hayne et al., 1997; Herbert & Hayne, 2000; Herbert et al., 2006). In Experiments 1 to 5 here, the demonstration and test toys differed in form and function as well as in color and size; they could not be construed as members of the same category. Thus, although infants may have learned something about particular kinds of objects from the demonstration trials, this object-specific knowledge was not the basis of their transfer to the novel test toy. Second, whereas in prior research the demonstration and test toys yielded the same effect when acted on, in Experiments 1 to 3 and 5 the toys all yielded different effects, and in Experiment 4 the demonstration toys did not yield an effect at all. Hence, knowledge of how to achieve a particular goal was not the basis of infants’ transfer, nor was any simple kind of operant reinforcement. We think that the critical component for infants’ transfer involved the action affordance of the knobs that the demonstration and test toys shared. From the demonstrations, infants learned that the knobs could be pressed or pulled and that these actions are interesting and desirable to apply to objects containing such knobs in general. Thus, they seemed to abstract or disentangle the knobs’ action affordances from the particular objects and effects for which they were first performed, then stored these affordances as entities in their own right, and later used them as means to explore new objects to new ends. This emphasis on the central role of the target actions for transfer is supported by the finding that transfer was more robust when infants practiced the actions themselves as opposed to just observing them on the demonstration trials. It is also supported by the fact that observing and practicing the action affordance alone, not attached to any complete object and not associated with any effect, nevertheless promoted robust transfer to a novel object. The idea that action affordances per se are what is transferred from imitation is consistent with claims that infants attend especially to the model’s behavioral methods when they observe goal-directed behaviors (Call & Carpenter, 2009; Nagell et al., 1993; Nielsen et al., 2008; Tomasello, 1999). However, with the transfer process, infants go beyond the information given by the model to apply the observed behaviors in a new context. This extension is similar to developments originally described by Piaget (1952), Piaget (1954), who wrote of infants beginning to differentiate means from ends at approximately 8 months of age and characterized the subsequent ‘‘stage” of cognitive development as ‘‘the application of familiar schemata (actions) to new situations” (Piaget, 1952, p. 212). Thus, transfer of the means as shown in our research represents an important synthesis of Tomasello’s (1999) emphasis on the role of culture for infants’ development and Piaget’s emphasis on infants’ proclivities for self-discovery. With transfer, infants learn low-probability behaviors from others but then use these behaviors of their own accord to explore new objects and discover new means–ends relationships. The potential for new discoveries it bestows is indeed the special advantage of transfer from imitation over imitation itself. When an action such as pressing or pulling is abstracted from the specific object on which it was first imitated, it becomes a sort of ‘‘free radical” that can be applied to many objects. The action affordance plays a role similar to that of a ‘‘pivot word” (cf. Braine, 1976) or ‘‘verb island” (cf. Tomasello, 1999) in language acquisition; as for language, this frame-slot action grammar permits generativity. With straightforward imitation, useful activities with objects can be transmitted from individual to individual, but a group’s technology might remain the same for generations, as it seems to in chimpanzee cultures, for example, chimpanzee cultures. But with free-wheeling transfer from imitation, the odds of fortuitously discovering new means–ends relationships increase dramatically and technological change is catalyzed. Paradoxically, with the capacity for transfer, imitation may be the root of invention.

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Acknowledgments Experiment 1 reported here was part of the research submitted by the second author to Tufts University for the master’s degree, and Experiment 4 was part of the research submitted by the second author to Tufts University for the PhD degree. We thank the following undergraduates for their help with testing the infants and scoring the data tapes: Christina Bruno, Jonathan Cohen, Jessica Fradkin, Rachel Fuchs, Shauna Gilmore, Daniel Greenwald, Everett Hendler, Jackie Houghton, Alex Kenny, Sarah Kerstein, Corrine Mahoney, Alex McCauley, Alice McMahon, Patrice Rice, Angie Rodday, Mara Sacks, Laura Sherman, Reuben Shin, Adrien Snow, Abby Svenson, and Johanna Thompson-Holland. We also extend our gratitude and best wishes to the families whose infants participated in the research reported here.

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