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How interpersonal synchrony facilitates early prosocial behavior

Laura K. Cirelli

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Cirelli LK. How interpersonal synchrony facilitates early prosocial behavior. Curr Opin Psychol. 2018;20:35–39. doi:10.1016/j.copsyc.2017.08.009

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How interpersonal synchrony facilitates early prosocial behavior 5

Laura K. Cirelli 6

Department of Psychology, University of Toronto Mississauga, 7

Mississauga, ON, L5L 1C6 8

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Corresponding author: Cirelli, L. (laura.cirelli@utoronto.ca) 10 This review comes from a themed issue on Early Development of Prosocial Behavior 11

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Abstract 1

When infants and children affiliate with others, certain cues may direct their social efforts 2

to “better” social partners. Interpersonal synchrony, or when two or more people move 3

together in time, can be one such cue. In adults, experiencing interpersonal synchrony 4

encourages affiliative behaviors. Recent studies have found that these effects also 5

influence early prosociality – for example, 14-month-olds help a synchronous partner 6

more than an asynchronous partner. These effects on helping are specifically directed to 7

the synchronous movement partner and members of that person’s social group. In older 8

children, the prosocial effects of interpersonal synchrony may even cross group divides. 9

How synchrony and other cues for group membership influence early prosociality is a 10

promising avenue for future research. 11

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Highlights 13

x When people move together in synchrony, they later behave more prosocially. 14

x This effect influences prosociality early, even in young infants. 15

x Synchrony can cue group membership, leading to directed prosociality. 16

x These effects raise exciting questions about social development more generally. 17

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Introduction 1

In the past decade, the influence of interpersonal synchrony on prosocial 2

behavior has attracted the attention of social psychology and music cognition 3

researchers. When two or more individuals move together in time-locked interpersonal 4

synchrony (e.g. by rowing, dancing, singing, marching, or tapping in time together), they 5

later experience greater social cohesion and engage in more prosocial behaviors [1–4]. 6

Synchronous compared to asynchronous movers are later more likely to rate one another 7

as likeable [1,5], to be more cooperative [2,6], and to display helpfulness [7]. While much 8

work in this area focuses on adult populations, there is a growing body of research with 9

infants and children that demonstrates how interpersonal synchrony influences early 10

social cognition and behavior [8–15]. This developmental work has interesting 11

implications for the social importance of interpersonal synchrony and about the 12

development of prosociality more generally. 13

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Box 1. Key Terms 15

Interpersonal synchrony: A specific class of coordinated action. This term describes a 16

series of movements by two or more individuals that unfold in a time-locked fashion. 17

Prosocial behaviors: Overt actions that encourage social cohesion by providing a benefit 18

to the social partner, e.g. trusting, cooperating, helping, comforting and sharing. 19

Social cohesion: Achieved when individuals have social bonds to one another and to the 20

group as a whole. The group is able to work toward common goals efficiently and with 21

unity. 22

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Social preferences: Liking of certain individuals over others. While the term refers to a 1

cognitive state, it often manifests behaviourally in infants as increased looking and 2

proximity seeking toward one individual over another. 3

Mimicry: Matching the movements of another individual. Unlike interpersonal 4

synchrony, these movements involve a time lag, and encourage prosociality only when 5

the target does not consciously notice being mimicked [2]. 6

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Synchrony Encourages Early Prosociality 9

Interpersonal synchrony influences early social preferences. By at least 12 10

months of age, infants already show a preference for a synchronous over an asynchronous 11

social partner [10]. In this experiment, infants were rocked gently in a car seat while 12

watching a life-like video of two teddy bears (one synchronous mover, one asynchronous 13

mover) also rocking in car seats. Afterward, infants were more likely to reach for and 14

select the synchronous over the asynchronous teddy bear. This effect was not found in 9-15

month-old infants [10], suggesting that synchrony directs infant preference later than 16

other social preference cues such as spoken language [16], displays of prosociality [17], 17

and the use of infant-directed speech [18]. This may be due to the multimodal complexity 18

of attending to and comparing own and other’s movements over time. For example, only 19

after 8 months of age do infants discriminate between audiovisual synchrony and 20

asynchrony in videos of dancers [19]. 21

Interpersonal synchrony also influences early prosocial behavior. In a series of 22

studies with 14-month-old infants [8,9,13,15], an assistant held and bounced infants for 23

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about two minutes either synchronously or asynchronously to the movements of the 1

experimenter who faced the infant. After this interpersonal movement experience, infants 2

would perform instrumental helping tasks (based on those developed in [20,21]) with this 3

main experimenter. The experimenter would pretend to accidentally drop objects that 4

were needed to complete a simple task (e.g. markers that were being used to draw a 5

picture), and the percentage of objects each infant handed back was recorded. In the first 6

experiment in this research program [8], infants in the synchrony condition handed back 7

significantly more of these objects than infants in the asynchrony condition, and helped 8

more quickly. These results, along with subsequent replications and extensions [9,13,15], 9

demonstrate that interpersonal synchrony can cue prosociality from an early age. In fact, 10

this is the earliest age at which helping behaviors have been measured in a laboratory 11

setting [21]. 12

While these infant studies focused on interactions with adults, studies with older 13

children have investigated the social effect of interpersonal synchrony between peers. For 14

example, 4-year-olds who experience high levels of interpersonal synchrony compared to 15

asynchrony are later more likely to be helpful [22,23], cooperative [23], and more 16

successful at coordinating their actions [24]. Eight-year-olds who participate in a group 17

singing activity are later more cooperative than children who participate in a group art 18

activity or a competitive games activity [25]. Relatedly, 8-year-old children who tap in 19

synchrony with a peer rate that child as more similar and socially close to them than an 20

asynchronously-tapping peer [12]. Future research may more explicitly test how 21

interacting mainly with adults during infancy and later with increasingly more peers 22

influences how interpersonal synchrony affects prosocial behavior across age groups. 23

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Synchrony Leads to Directed Helpfulness and Cues Group Membership 1

The established link between synchrony and prosociality raises the question about 2

the specificity of this effect. Does experiencing interpersonal synchrony put us in a 3

prosocial “mood”, encouraging indiscriminate prosociality? Or does it specifically direct 4

our prosociality toward only our synchronous movement partner(s)? Infant research using 5

the bouncing/helping paradigm described above tested 14-month-old helping toward the 6

main movement partner (synchronous or asynchronous), as well as toward a neutral 7

experimenter who sat passively in the corner reading a book during the bouncing [9]. 8

Replicating the previous findings [8], infants in the synchronous condition helped their 9

movement partner more than infants in the asynchronous condition. However, there was 10

no effect of movement condition on neutral stranger helping. Helping this person was 11

instead related to infant sociability, as reported by parents. This supports the hypothesis 12

that interpersonal synchrony encourages directed prosociality (however, see Box 2 for a 13

discussion on how long-term musical engagement may encourage general prosociality). 14

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Box 2. Does Music Training Encourage General Prosociality? 16

While short-term experiences of interpersonal synchrony in a dyadic context encourage 17

directed helpfulness [9], there is evidence that long-term involvement with group music 18

training may have more general effects on social cognition and behavior. These music 19

classes encourage high levels of interpersonal synchrony in a group context. In school-20

aged children, involvement in a group music class at school for an entire school year 21

reportedly improved emotional empathy, sympathy and prosocial attitudes [26,27]. 22

Involvement in parent-infant group music classes improved parent-rated infant sociability 23

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and infant emotional understanding [28]. Of interest is whether these effects are driven by 1

long-term involvement in a highly synchronous activity and/or by other components of 2

musical engagement. While synchrony has been shown to influence prosociality even in 3

non-musical contexts [1,2,6,15], the emotion-regulating properties of music may work 4

with synchrony to make musical engagement an important social tool. 5

These findings have implications on how infant helping is directed to certain 6

social partners over others, and supports the “partner choice” model of prosociality [29]. 7

Young infants direct social attention to individuals who display cues for self-similarity 8

(language [16], race [30]) and cues for prosociality (helpers over hinderers [17]). Older 9

infants will direct prosociality to a well-intentioned experimenter over a selfish one [31]. 10

Such findings suggest that certain social cues (e.g., similarity, prosociality, synchrony) 11

encourage directed prosociality. Other social cues, like mimicry [32] and social priming 12

[33], may instead encourage generalized prosociality. For example, 18-month-old infants 13

who are mimicked by an experimenter compared to those who are not will later hand 14

more dropped pencils back to both the mimicking experimenter as well as a neutral 15

stranger [32]. Cues that encourage directed helping may facilitate partner choice, while 16

cues that encourage indiscriminate helping may instead influence infant social mood. 17

How and when infants use social cues to select “good” social partners is an exciting area 18

for future research. 19

Another interesting component of partner choice relates to the idea of social 20

transitivity [34]. That is, if an infant feels more prosocial toward Experimenter A after 21

synchronous bouncing, will they also help the friends of this experimenter? To explore 22

this using the bounce/help paradigm with 14-month-olds, infants first watched a short skit 23

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performed by the main experimenter and a confederate [13]. This skit either demonstrated 1

to the infant that these two individuals were friends (they greeted one another happily, 2

and had a short dialogue) or that they were independent actors (they performed two 3

separate monologues, matched to the dialogue condition in plot, valence, and overall 4

length). Infants then bounced either in- or out-of-synchrony with the main experimenter, 5

but performed instrumental helping tasks only with the confederate. If infants performed 6

these tasks with the independent experimenter (i.e., the “non-friend”), helping remained 7

near baseline regardless of the synchrony manipulation. If, however, the infant interacted 8

with the “friend” of the bouncer, they responded to this individual as though they were 9

interacting directly with the main experimenter – helping more in the synchronous 10

condition than the asynchronous condition. These findings suggest that interpersonal 11

synchrony encourages directed infant prosociality toward a synchronous movement 12

partner, and also toward members of that person’s social group. This raises interesting 13

questions about how infants understand third-party relationships and utilize this 14

understanding to direct affiliative behaviors. 15

These findings also support the idea that synchrony is a cue for group 16

membership. If this is the case, then synchrony with an out-group member may reduce 17

out-group negativity. In a recent study, small groups of 8-year-old children were 18

randomly assigned to be part of the green group or the orange group and wore 19

corresponding colored vests [11]. This form of “minimal group” assignment reliably 20

generates in-group favoritism and out-group negative biases [35]. The two groups were 21

then trained to perform a series of dance moves in time to an auditory rhythm presented 22

to each child via wireless headphones. In the synchrony condition, the children from both 23

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groups would match their movements to the same rhythm. In the asynchrony condition, 1

the children from one group would match their movements to a rhythm that was either 2

faster or slower than that presented to the second group. Synchronous compared to 3

asynchronous inter-group movement led children to feel more bonded with the out-group 4

and more willing to seek physical proximity to members of the out-group. This 5

experiment suggests that synchronous inter-group movement can reduce negative out-6

group biases in a minimal group context [11]. The effectiveness of inter-group synchrony 7

in reducing negative out-group biases against more salient groups (i.e. sex, race and 8

language categories) is a promising direction for future research. 9

Possible Mechanisms: Cognitive and Neurohormonal 10

There are several proposed explanations for why interpersonal synchrony 11

influences prosocial behavior. One idea is that synchrony is a low-level cue for self-12

similarity, and these feelings of self-similarity encourage empathy and in-group 13

affiliation [36]. Supporting this, children and adults judge synchronous peers as more 14

self-similar than asynchronous peers [12,36], and adults show more compassion for 15

synchronous over asynchronous others [36]. This proposal fits well with the idea that 16

synchrony is a cue for group membership, and with the idea that synchrony influences 17

various forms of prosocial behavior. Another proposal is that attention is drawn to 18

synchronous movers, and through mere exposure and increased person-perception we 19

become more likely to affiliate with these partners [37]. 20

An important question for future research is how synchrony influences 21

helpfulness. When infants see a person in need of help, pupil dilation measures show 22

sympathetic arousal in response to that need [38]. These arousal levels are positively 23

10

correlated with infant helping. However, arousal recovers whether the infant provides 1

help, or if another person provides help [38]. Do infants help more following 2

interpersonal synchrony because of increased arousal in response to their synchronous 3

partner’s distress, or an increased desire to get credit for providing help [39]? 4

In an attempt to uncover the underlying mechanisms driving the effects of 5

synchrony on prosociality, there is also a growing interest in how social synchrony can 6

influence neurohormonal factors, particularly endorphins and oxytocin. Adult studies 7

have shown that social synchrony (i.e. dancing, rowing, or singing) compared to 8

asynchrony or moving alone can increase pain thresholds, a proxy for endorphin release 9

[3,40–42]. Endorphins have been linked to social bonding in non-human mammals 10

(reviewed in [43]), and so release during interpersonal synchrony may underlie the 11

affiliative consequences of synchronous movement. 12

Oxytocin is another neuropeptide that has been associated with social bonding and 13

social cognition [44]. A recent study investigated the role of oxytocin in coordinated 14

finger tapping [45]. Dyads received intranasal oxytocin or placebo and were then asked to 15

complete a simple tapping task. Participants given oxytocin were better than controls at 16

following and synchronizing with an unresponsive partner. Relatedly, intranasal oxytocin 17

improves behavioral synchrony and inter-brain synchrony [46]. This new area of research 18

on how oxytocin contributes to interpersonal coordination is especially promising, given 19

that oxytocin is also released during parent-infant interactions [47], choral singing [48], 20

and when falling in love [49]. Interpersonal synchrony may potentially facilitate parent-21

infant bonding through the release of oxytocin. 22

Conclusions and Future Directions 23

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Presented here is a brief overview of how interpersonal synchrony can influence 1

early prosociality. I present the argument that synchrony is a cue for group belonging and 2

that it encourages directed and transitive prosociality. The work in this area has raised 3

questions that are of interest to social development researchers in general. For example, 4

how and why do infants direct prosociality to certain partners over others? What social 5

cues encourage directed versus generalized prosociality? Can cues for group membership, 6

like interpersonal synchrony, be used to reduce negative out-group biases? What 7

cognitive and neurohormonal mechanisms contribute to this effect? The study of how 8

interpersonal synchrony influences early prosociality has only recently captured the 9

attention of researchers, and is a field rich with research potential. 10

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Acknowledgements 13

This work was supported by a Postdoctoral Fellowship from the Social Sciences and 14

Humanities Research Council of Canada. Thank you to Haley Kragness for helpful 15

comments on an earlier draft. 16

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