Third-Party Preferences for Imitators in Preverbal Infants

Participants in social interactions often imitate one another, thereby enhancing their affiliation. Here we probe the nature and early development of imitation-based affiliation through studies of infants’ preferences for animated characters who imitate, or are imitated by, other characters. Four experiments provide evidence that preverbal infants preferentially attend to and approach individuals who imitate others. This preferential engagement is elicited by the elements of mimicry in simple acts of helping. It does not, however, extend to the targets of imitation in these interactions. This set of findings suggests infants’ imitation-based preferences are not well explained by homophily, prestige, or familiarity. We propose instead that infants perceive imitation as an indicator of valuable attributes in a potential social partner, including the capacity and motivation for social attention and coordinated action.

Infants imitate both actions and sounds by the end of the first year (e.g., Barr, Dowden, & Hayne, 1996;Jones, 2007;Meltzoff, 1988), but their motives in performing these actions, and their interpretation of imitative acts, are not clear.A few studies suggest that toddlers in the second year appreciate the social value of imitation and respond positively to those who imitate them (Agnetta & Rochat, 2004;Carpenter, Uebel, & Tomasello, 2013;Meltzoff, 1990), but little evidence suggests whether observed acts of imitation carry social meaning for younger infants.
A recent series of experiments addressed this question by asking if 4-and 5-month-old infants who observe imitative interactions as third parties expect the interaction partners to affiliate with one another (Powell & Spelke, 2018a).First, infants observed animated events depicting one character engaging in imitative and nonimitative interactions with two separate social parties.Then, across several experiments, a violation of expectancy looking time method was used to test (1) if infants expected the targets of imitative and nonimitative responses to approach partners who had imitated them, and (2) if infants expected responding characters to approach targets they had or had not imitated.Looking times indicated that infants did expect responding characters to approach and affiliate with the social partners they had imitated, Powell, Spelke though the strength of this expectation was graded, yielding reversals in looking preferences as display complexity and participant age varied, and no looking preferences under conditions of intermediate complexity.In contrast, infants' looking patterns provided no evidence of expectations that target characters would approach those who imitated them over those who did not.

Preferences for Imitators in Preverbal Infants
These findings provide evidence that imitation carries social meaning for young infants, but do not reveal what that meaning is.Do infants expect imitators to approach their targets because they view them as similar to one another?Because they view the targets as more prestigious?As more desirable?Or do infants expect others to approach the individuals that they imitate because both imitation and approach are indicative of the imitator's prosocial nature or orientation toward the target?To approach these questions, here we ask if infants themselves prefer individuals who imitate, or are imitated by, others.For most of the infants we tested, these experiments began when the above studies ended: after infants viewed two characters interact imitatively or nonimitatively with a third character, and then either approach or be approached by that character (Powell & Spelke, 2018a, Experiment 4).Following these displays, we tested infants' relative preference between the imitating and nonimitating characters.With these studies, we seek to better characterize the social value of imitation for infants.
Four hypotheses make largely nonoverlapping predictions regarding infants' potential preferences for imitators over nonimitators and for targets of imitation over nontargets, following third-party observations of imitative interactions.According to the hypothesis of homophily-a liking for similar others (Byrne & Griffitt, 1966;Fawcett & Markson, 2010;Mahajan & Wynn, 2012;Neimeyer & Mitchell, 1988)-participants in social interactions interpret imitators' reproduction of their actions as evidence of similarity to themselves (Haun & Over, 2015;Lakin, Jefferis, Cheng, & Chartrand, 2003).This hypothesis predicts that thirdparty observation of imitation will not affect the observer's social preferences: observations of imitation should only increase infants' perception of the imitator's similarity to its target, not to the infant.
A second hypothesis is based on the finding that familiarity engenders preferences at all ages (Cooke, 2007;Peery & Peery, 1986;Zajonc, 1968), including infancy (e.g., bar-Haim, Ziv, Lamy, & Hodes, 2006;Kinzler, Dupoux, & Spelke, 2007;Mehr, Song, & Spelke, 2016).In the context of imitative and nonimitative interactions, infants could develop a preference for both the imitator and the target on the basis of greater accumulated familiarity with the imitated behavior, which would be performed more frequently.
Third, infants may view imitation primarily as an indicator of the prestige, or social value, of the target of imitation.Thus they may prefer such targets to those who are not targeted by acts of imitation, as do older children and adults (Chudek, Heller, Birch, & Henrich, 2012;Henrich & Gil-White, 2001;Over & Carpenter, 2015), while showing no preference for imitators over nonimitators.
Finally, infants' preferences may be elicited by the distinguishing characteristic of imitation: alignment with the behavior of others.Such alignment may provide evidence of the imitator's prosocial capacities and motivation toward social engagement, while providing no evidence regarding the prosocial capacities or motivation of the target.Thus, infants who observe imitative interactions may prefer imitators to nonimitators, but not targets to nontargets.
Experiments 1 and 2 begin testing these predictions by assessing 4.5-month-old infants' preferential looking to two characters who each respond to a third character's action, one Powell, Spelke by imitating the action and the other by performing a contrasting action.Experiment 3 tests infants' relative preference between two characters who act in turn, one receiving an imitative response from a third character and the other receiving a contrasting response.Finally, Experiment 4 builds on positive evidence of preferential attention to imitators over nonimitators from Experiments 1 and 2 by testing whether 12.5-month-old infants preferentially reach for characters who imitate their social partners.In all experiments, interactions between characters were presented using animated displays run by display-blind experimenters, allowing us to assess infants' preferences using consistent events and unbiased experimenters.

Methods
We recruited 48 4-to 5.5-month-old infant participants from the greater Boston area.Forty of these infants were tested in conjunction with participation in Experiment 4 of Powell & Spelke (2018a), which evaluated infants' expectation of approach between imitators and targets.The main analyses of the current experiment did not involve the approach events, but rather tested infants' relative preference for imitating and nonimitating characters during a subsequently conducted preferential looking test.(Looking times to approach events were examined only to rule out potential influence on preferential looking; see the Supplemental Materials [Powell & Spelke, 2018b].)As a result of this difference in analytical focus, the two experiments had small differences in inclusion criteria.The eight nonoverlapping infants in the current sample were either recruited to replace participants from the previous experiment who did not meet the inclusion criterion for this experiment of looking to each character during the preference test for a minimum of 1 s or retained for this experiment but replaced in the approach experiment due to inattentiveness during approach events.These infants completed the same full procedure as the 40 infants that overlapped with Powell and Spelke (2018a).For details on these two sets of subjects, as well as subject demographics, inclusion criteria, and informed consent, see the Supplemental Materials (Powell & Spelke, 2018b).
The experiment consisted of three phases.In the first phase, infants viewed three animated characters engaging in pairwise interactions.Each interaction began with the central character (the target) jumping three times, making the same sound at the start of each jump.Then one of the side characters responded by jumping and making either the same or a different sound.Across eight events, the two side characters responded in alternation, one producing the same sound as the target (the imitator) and one producing a different sound (the nonimitator; Figure 1a; Movie S1 [Powell & Spelke, 2018b]).
In the next phase, infants saw approach events in which one character moved toward another, and then the two characters moved synchronously around a circular path (Figure 1b; Movie S1 [Powell & Spelke, 2018b]).After completing this path, the characters remained motionless on the screen while a display-blind coder tracked looking to the display.This infantcontrolled pause ended after 60 s of cumulative looking or 2 s of consecutive looking away.Half of the participants saw responder approach events, in which the imitator and nonimitator alternately approached the target, and half saw target approach events, in which the target alternately approached the imitator and nonimitator (see the Supplemental Materials [Powell & Spelke, 2018b] and Powell & Spelke, 2018a, for use of these events to test infants' inferences of affiliation between imitators and targets).
Finally, we tested infants' relative preference for the imitator and nonimitator.A displayblind experimenter held a pair of disc-shaped objects with the same appearance as the imitator and nonimitator (Figure 2c) ∼40 cm apart, centered in front of the infant but beyond reaching distance, for 20 s.Offline, condition-blind coders determined how much time infants spent looking at each character.We compared these looking times using a repeated-measures ANOVA, including interaction order (imitation first or second), approach type (responder or target), imitator identity (right-or left-side character), and imitated sound (high or low) as between-subjects factors.Looking times to imitative and nonimitative interaction events and congruent and incongruent approaches were compared similarly.(For additional procedural details and reliability coding, see the Supplemental Materials [Powell & Spelke, 2018b].)

Preferences for Imitators in Preverbal Infants
Although we did not predict that the approach events would influence infants' preferential attention to the imitator and nonimitator, post hoc consideration suggests two potential origins of this effect.First, the responder approach events may be necessary to elicit an imitator preference.Infants may, for instance, prefer to attend to characters whose social behavior is consistent over time, that is, who respond to a social partner by both imitating and approaching him.Alternatively, the target approach events may have interfered with a preference for imitators, established in the interaction phase.Infants may prefer imitators over nonimitators, but that preference may be attenuated or erased if both are approached by the character who initiated the interactions, thereby signaling that both responding characters are valued.Experiment 2 distinguished these possibilities.

EXPERIMENT 2
Experiment 2 tested infants' preference for imitators over nonimitators in the absence of any approach events.

Methods
We recruited 24 novel 4-to 5.5-month-old participants.The interaction events and preferential looking test were identical to those of Experiment 1, except that each pair of interactions was followed by an infant-controlled pause during which the characters remained motionless onscreen (see the Supplemental Materials [Powell & Spelke, 2018b]).No approach events were presented.

Results and Discussion
During familiarization, infants looked equally at the imitative (10.68 s) and nonimitative interactions [10.90 s; F(1, 16) = 0.96, p > .3].Thus, the increased attention to nonimitative interactions found in Experiment 1 was not replicated in this study.During the subsequent preference test, infants spent significantly more time looking at the imitator (6.70 s) than the nonimitator [4.40 s; F(1, 16) = 9.35, p < .01; Figure 2a; for comparison with Experiment 1, see the Supplemental Materials (Powell & Spelke, 2018b)].The approach events therefore were not necessary to produce preferential attention to the imitator.Instead, the target approach events evidently weakened infants' preference for the imitator, either by increasing the social value of both responding characters or by drawing infants' attention away from the responders and toward the target.

EXPERIMENT 3
The preferential attention to imitators observed in Experiments 1 and 2 is consistent with the hypothesis that infants prefer individuals who imitate their social partners, perhaps because such alignment reflects the imitator's prosocial capacities or motivations.However, alternative explanations remain.Infants may have preferred the imitator because the sound it made occurred

Preferences for Imitators in Preverbal Infants
Powell, Spelke more frequently and therefore became more familiar than the sound made by the nonimitator.Although homophily alone cannot explain infants' preference, as the infants themselves did not (and, indeed, cannot) produce the imitated sounds, perhaps infants prefer imitators and targets with homophilous relationships to one another.Moreover, apart from any preference for the imitator, infants may also perceive the targets of imitation as prestigious or socially valued individuals.All of these hypotheses predict that if we reverse the roles of the characters in the interactions from Experiments 1 and 2, such that the side characters are either imitated by the central character or not, then infants will prefer the character who is the target of imitation to the nontarget.Experiment 3 was undertaken to test this prediction.

Methods
Seventy-two 4-to 5.5-month-old infants participated.Forty infants were tested in conjunction with their participation in Experiment 4 of Powell and Spelke (2018a; see the Supplemental Materials [Powell & Spelke, 2018b] for details on this joint participation, and for a comparison of looking times to approach events in the two overlapping samples).The interaction events were identical to those of Experiments 1 and 2, except that the side characters now jumped and vocalized first, and the central character responded to each of them, imitating one (the target of imitation) and not the other (the nontarget; Figure 3a; Movie S2; see details in the Supplemental Materials [Powell & Spelke, 2018b]).Twenty-four infants participated in each of three conditions that paired these new interaction events with the same approach events used in Experiments 1 and 2 (Figure 3b): events in which the center character alternately approached the side characters (now responder approach events, given the reversed interaction roles), events in which the side characters alternately approached the center character (now target approach events), or no approach events at all.The preference test remained unchanged.

Results and Discussion
Infants looked equally to the imitative (M = 10.98 s) and nonimitative interactions [M = 10.76 s; F(1, 45) = 1.09, p > .3].Looking times to the congruent and incongruent approach events also did not differ from one another or from those of the overlapping sample of participants in the Powell and Spelke (2018a) experiment (see the Supplemental Materials [Powell & Spelke, 2018b]).Powell, Spelke another puppet who has attempted the same climb, or tosses back a ball that another puppet has tossed to him, or pulls upward on the lid of a box that another puppet also has attempted to lift (e.g., Hamlin et al., 2007;Hamlin & Wynn, 2011;Kuhlmeier, Wynn, & Bloom, 2003).The imitative nature of these acts of helping raise the possibility that infants' preference for helpers is driven by the helper's imitation of the beneficiary, rather than by the helper's impact on the achievement of the beneficiary's goals.Experiment 4 tests the feasibility of this interpretation by asking if infants recognize the mimicry involved in a helping behavior and prefer those who engage in this mimicry, even if the context is changed such that the behavior is not, in fact, helpful to the beneficiary.

Preferences for Imitators in Preverbal Infants
The experiment was modeled on a helping scenario featuring a protagonist who attempts to climb a hill, as well as a helper who pushes the protagonist to the top and a hinderer who pushes the protagonist toward the bottom (Hamlin et al., 2007).The current events differed in one crucial respect: the actions of the former helper (now the imitator) and hinderer (now the nonimitator) were arranged such that they did not impact the achievement of the protagonist's goal.The experiment concluded with the measure of preference most often used to assess infants' relative preference for helpers and hinderers: a preferential reaching test.

Methods
Sixteen 11.5-to 13.5-month-old infants saw six interaction events featuring three characters, all initially positioned at the top of the screen above a hill (Figure 4a).In each event, the central character moved from the bottom of the hill up to a middle platform and then engaged in two failed attempts to climb the second slope (Hamlin et al., 2007;Kuhlmeier et al., 2003).In imitative interaction events, one of the two remaining characters landed in front of the central character and copied its efforts to climb the hill, successfully reaching the upper platform on the second attempt.In nonimitative events, the other character landed on the top of the hill and then moved down the upper slope and back up twice, ending on the top platform where it started (Movie S3).Each interaction event was followed by an infant-controlled pause.Then a display-blind experimenter presented the infants with physical copies of the imitator and nonimitator, testing which character infants would reach for first (see the Supplemental Materials [Powell & Spelke, 2018b] for details).

Results and Discussion
During familiarization, looking times following imitation events (M = 10.19 s) did not differ from those following nonimitation events [M = 11.76 s; t(15) = 1.30, p > .2].Infants were significantly more likely to reach for the imitator than the nonimitator (13/16, binomial  Powell, Spelke probability test: p < .05; Figure 4c).Low-level aspects of the characters' motion are unlikely to account for this result, because infants look and reach equally for agents who go uphill versus downhill in the absence of a social partner (Hamlin et al., 2007), and both test characters moved toward and away from the central character to similar extents.These results thus extend the preference for imitators observed in the first two experiments to a new age, a new measure of preference, and a new target action that has received considerable attention in studies of infants' response to helpful and unhelpful agents.It is possible that infants have a true preference for those who help others.When a helpful action involves imitating the beneficiary's attempted efforts, however, this matching can elicit an imitation-based preference even in the absence of the helpful effect.Research investigating infants' preference for helpers therefore should present either nonimitative helping behaviors or should test infants' preference for characters who imitate with helpful versus neutral consequences.

GENERAL DISCUSSION
The present experiments provide four main findings.First, 4.5-month-old infants preferentially attend to parties who imitate the sounds made by their interaction partner over parties that respond nonimitatively (Experiments 1 and 2).Second, when the same imitative and nonimitative responses are directed toward two different targets, infants fail to show any preference to attend to the imitated target (Experiment 3).Third, infants' third-party preference for imitators generalizes across age groups (∼4.5 and 12.5 months), imitation modality (sound and motion), and behavioral measures (preferential looking and reaching).Finally, at least some helpful behaviors involve imitative components that can elicit a preferential approach from infants in the absence of any helpful impact.
The current findings align with prior research, supporting a cohesive picture of young infants' responses to social imitation.The prior research suggested that imitative interactions carry social meaning for young infants, insofar as they support expectations of imitators' future affiliative behavior (Powell & Spelke, 2018a).The present finding that infants' themselves prefer imitators suggests that young infants perceive imitation as a prosocial action that both indicates the imitator's affiliative motivations toward its target and warrants positive evaluation of the imitator.Future research can further test this hypothesis by characterizing the parameters that affect infants' preferences.Comparing responses to imitators, nonimitators, and nonresponding individuals can determine whether infants prefer imitators, disprefer nonimitators, or both.Research varying the characters' animacy or access to one another can test if infants' preference is rooted in a perception of the imitator and target as interaction partners.(For preliminary evidence that infants' preference depends on the imitator's perceptual access to the target's behavior, and for further evidence that infants preferentially approach imitators in a larger sample of participants, tested with the reaching method used here, see Powell & Spelke, 2017.)What could account for the perception of imitators as prosocial?As detailed above, neither homophily nor familiarity preferences can explain the current findings.We suggest instead that a preference for imitators helps infants (and older children and adults) identify individuals with the capacity and motivation for social engagement.Interacting with or helping a social partner requires abilities and propensities for social perception and attention and for socially coordinated action.Because imitation demonstrates these building blocks of prosocial behavior, infants' preference for imitators may therefore foster engagement with prosocial individuals, even before infants achieve the action representations and goal attributions required for understanding acts of helping and cooperation.

Figure 1 .
Figure 1.Illustrations of events from Experiments 1 and 2.

Figure 2 .
Figure 2. Preferential looking results.(a) Looking times to the imitator and nonimitator (Experiments 1 & 2), and (b) looking times to the target and nontarget of imitation (Experiment 3), divided by the paired approach events (RA = Responder Approach; TA = Target Approach; NA = No Approach condition).Error bars represent standard error of the mean.(c) Physical characters presented during preference test.

Figure 4 .
Figure 4. Scenes and preferential reaching results, Experiment 4. (a) Imitative action by the yellow character.(b) Physical characters presented during the reaching test.(c) Number of infants that reached first for the imitator and nonimitator.