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Ann. N.Y. Acad. Sci. ISSN 0077-8923
ANNALS OF THE NEW YORK ACADEMY OF SCIENCES
Issue: The Neurosciences and Music V
Rhythm and interpersonal synchrony in early social
development
Laurel J. Trainor1,2,3 and Laura Cirelli1
1Department of Psychology, Neuroscience and Behaviour, McMaster University, Hamilton, Ontario, Canada. 2McMaster
Institute for Music and the Mind, Hamilton, Ontario, Canada. 3Rotman Research Institute, Baycrest Hospital, Toronto, Ontario,
Canada
Address for correspondence: Laurel J. Trainor, Department of Psychology, Neuroscience and Behaviour, McMaster University,
1280 Main Street West, Hamilton, ON, Canada L8S 4B2. ljt@mcmaster.ca
Adults who engage in synchronous movement to music later report liking each other better, remembering more
about each other, trusting each other more, and are more likely to cooperate with each other compared to adults
who engage in asynchronous movements. Although poor motor coordination limits infants’ ability to entrain to
a musical beat, they perceive metrical structure in auditory rhythm patterns, their movements are affected by the
tempo of music they hear, and if they are bounced by an adult to a rhythm pattern, the manner of this bouncing
can affect their auditory interpretation of the meter of that pattern. In this paper, we review studies showing that by
14 months of age, infants who are bounced in synchrony with an adult subsequently show more altruistic behavior
toward that adult in the form of handing back objects “accidentally” dropped by the adult compared to infants
who are bounced asynchronously with the adult. Furthermore, increased helpfulness is directed at the synchronized
bounce partner, but not at a neutral stranger. Interestingly, however, helpfulness does generalize to a “friend” of the
synchronized bounce partner. In sum, synchronous movement between infants and adults has a powerful effect on
infants’ expression of directed prosocial behavior.
Keywords: rhythm; entrainment; interpersonal synchrony; infant development; prosocial behavior; altruism
Introduction
It is intriguing that humans not only have a propen-
sity to move to rhythmic auditory stimuli but also
they commonly engage in this activity in groups
where social bonding is important and shared goals
are desired.1For example, music and movement
(including dance) are commonly present during re-
ligious and ritual ceremonies, important commu-
nity events such as weddings and funerals, social
parties, and during group military exercises, sug-
gesting that engaging in music increases coopera-
tion within groups.2–6 In this paper, evidence for a
link between synchronous movement and prosocial
behavior in adults is reviewed, prerequisites for such
behavior are considered, and evidence for the influ-
ence of synchrony on helping behaviors in infancy is
presented.
Synchrony and prosocial behavior in
adults
Research indicates that synchronous movement
between adults increases group cohesion and social
cooperation.7–9 Synchronized movement appears to
have prosocial effects whether or not it involves
music, but the temporal predictability of musical
rhythms provides an ideal context to support syn-
chronized movement. Wiltermuth and Heath,9for
example, found that adults who walked together in
synch or moved a cup in synch while singing were
subsequently more likely to cooperate in a weak-
link game (where the best outcome for all is when
everyone contributes at the highest level, but if one
person contributes at a low level, those contributing
at a high level suffer most) and to contribute more
into a public account in a public-goods game (where
doi: 10.1111/nyas.12649
45
Ann. N.Y. Acad. Sci. 1337 (2015) 45–52 C⃝2014 New York Academy of Sciences.
Interpersonal synchrony and social development Trainor & Cirelli
the group benefits from contributions, but individ-
uals benefit from not contributing) compared to
people who did similar activities but not in synch.
Synchronous movement also increases trust7,10 and
affiliation11 between those involved. Furthermore,
people are more likely to engage in altruistic acts
(defined as acts that require personal sacrifice)
aimed at people with whom they previously moved
in synch compared to out of sync.9,12 Although the
mechanisms by which these social effects of syn-
chronous movement operate are not yet entirely
understood, people rate synchronously moving
partners as more similar to themselves than asyn-
chronously moving partners,8,12 and show enhan-
ced perception of, and memory for, synchronously
moving partners.8,13,14 Interestingly, one study in-
dicates that synchronized drumming increases
activity in the striatum (specifically the caudate),
an area associated with reward (both material and
social), prosocial behavior, and modulation of fut-
ure behavior.15
Prerequisite processes and their
development
Anumberofprerequisiteprocessescanbeidenti-
fied that are necessary to establish a causal connec-
tion between synchronous movement and prosocial
behavior in the context of music. The metric struc-
ture of the music must be extracted from the musi-
cal surface. The ability to connect motor movements
with theauditory beats of themusic mustbe present.
Whether or not other people are also moving in
synch must be perceived, for example, from see-
ing their movements or hearing the results of their
movements. Some understanding of people as social
agents must be present. And, finally, some appraisal
such as of self-similarity must be made, which
affects affiliative evaluation, social perception, and,
ultimately, prosocial or altruistic behavior. Music is
particularly interesting with respect to early social
development because caregivers across cultures sing
to infants,16,17 and this singing is used to communi-
cate emotionally and to help infants regulate their
state.18
Development of the perception of metrical
structure
Musical rhythms consist of patterns of event onset-
to-onset of different durations. From at least as
young as 2 months of age, infants can discriminate
changes in tempo19 and changes in simple rhythmic
patterns.20–22 From musical rhythm patterns, adults
readily extract a steady underlying beat or pulse to
which they might clap their hands or tap their foot.
These beats can be arranged in different percep-
tual groups or meters. For example, every second
beat might be accented, resulting in a duple me-
ter (e.g., a march), or every third beat might be
accented, resulting in a triple meter (e.g., a waltz).
At some levels of the metrical hierarchy, beats will
be evenly spaced (isochronous), but at others they
might be nonisochronous but regular (e.g., alter-
nating groups of two and three beats). Sensitivity to
meter emerges early in development. Perceptually,
7-month-old infants show surprise when a meter is
changed from duple to triple or vice versa.23 There is
even evidence that newborns may extract the meter
from auditory rhythm patterns in that they show
larger event-related potential mismatch negativity
responses to the omission of a strong beat compared
to a weak beat in an ongoing rhythm pattern.24 The
particular meters commonly used vary from musi-
cal system to musical system, and infants’ perception
becomes specialized for the meters in the music in
their environment by the end of the first year after
birth.25 In sum, infants perceive metric structure
very early on, and their perception is shaped by
experience during infancy.
Development of the ability to entrain
movement to an auditory beat
Many species execute rhythmic movements, includ-
ing those used in locomotion (e.g., walking, run-
ning, hopping, swimming, flying), feeding (e.g.,
chewing, pecking), and sound production (e.g., vo-
cal cord vibration, limb or wing rubbing). Many
species also synchronize movements across indi-
viduals, such as fireflies that pulse together, birds
that flap their wings together, and fish that move
their fins and tails together. However, few species
have been shown to synchronize rhythmic move-
ments with an external auditory beat.26,27 Although
the vast majority of humans readily, even sponta-
neously, engage in movement to a predictable beat
such as that found in music,26,28–30 convincing evi-
dence of this in other species has been found only
for a few vocal learning birds31,32 and one sea lion
who was trained in captivity.33
Developmentally, it takes years for human chil-
dren to become adept at synchronizing movements
46 Ann. N.Y. Acad. Sci. 1337 (2015) 45–52 C⃝2014 New York Academy of Sciences.
Tra i n o r & Cir e l li In t e r per s o n a l syn c h ron y a n d s oci a l d e v elo p m e nt
with an auditory beat. For example, 3-year-olds are
poor at clapping in time with a metronome beat,34
a task that is easy for adults.28 The tempo range
over which young children can produce a steady
beat when they clap is restricted to beat onset-to-
onset times around 400 ms,35 whereas adults are able
to synchronize across a wide range of tempi.29,30
Furthermore, the limitations in young children’s
entrainment abilities do not appear to be restricted
to clapping movements; although young children
will move to music by hopping, swaying, and cir-
cling, these movements are generally not related to
the tempo of the music.36 By 4 years of age, children
begin to demonstrate robust entrainment.34,35,37,38
Interestingly, when entrainment is socially sup-
ported, children as young as 2.5 years show some evi-
dence of entrainment; at this age, children showed
evidence of entrainment when drumming with a
human partner but not when drumming with a
machine that hit the drum.39 Although 4.5-year-old
children could entrain their drumming in both con-
ditions, they were more accurate when drumming
with the human than the machine partner.
Given that even young infants perceive metric
structure in rhythm patterns, it is possible that
young children’s poor ability to entrain is due in
large part to motoric immaturity. Indeed, although
infants 5–18 months old were found not to entrain
to music, they did move more in response to music
than to speech and tended to move faster to music
with faster tempi.40 This suggests that the connec-
tions between motor and auditory systems may be
present early in development, but the limiting factor
is actual motor control of movement.
One way to examine early connections between
motor and auditory regions is to actually move in-
fants (rather than expecting them to execute the
movements) and determine whether this has an
influence on auditory perception. Phillips-Silver
and Trainor41 did just this. They presented infants
with an ambiguous auditory rhythm pattern, that
is, one that could be interpreted metrically in more
than one way. Specifically, they presented a repeating
six-beat pattern with no physically accented beats
that could be perceived either as two three-beat
groups (as in a waltz) or as three two-beat groups (as
in a march). Half the infants were held and bounced
on every second beat and half on every third beat.
After 2 min of this movement experience, using a
paradigm in which infants controlled how long they
listened to each pattern by their head movements,we
found that infants preferred to listen to the rhythm
pattern with accents that matched how they had
been bounced. That is, infants bounced on every
second beat of the nonaccented ambiguous pattern
preferred to listen to a version of the pattern with
accents added on every second beat, whereas infants
bounced on every third beat of the nonaccented
ambiguous pattern preferred to listen to a version
of the pattern with accents on every third beat. From
this study it can be concluded that strong links exist
for rhythm between motor and auditory domains
in infancy, as in adulthood.42,43
In adults, fMRI studies indicate that simply lis-
tening to an auditory rhythm activates motor net-
works in the brain.44–47 EEG and MEG studies
show that responses from auditory cortex follow
the tempo of the music48,49 and that listening to
an auditory rhythm causes oscillatory activity in
the !band (around 20 Hz) in both auditory and
motor regions.50 One study shows similar entrain-
ment of oscillatory !-band responses to the tempo
of an auditory rhythm in school-aged children,51
but the neural underpinnings of entrainment in inf-
ants have not yet been investigated. In any case,
the existing literature shows that prerequisite entr-
ainment abilities, namely the association between
auditory and motor interpretations of meter and
rhythm, are present in infancy to support links bet-
ween movement synchrony and social behavior.
Early development of social understanding
Increasing evidence suggests that humans are most
different from other species, including those that
humans are most closely genetically related to, with
respect to social cognition52 and that by 1 year of
age, social development is well under way.53 Motor
entrainment between individuals is a specialized
form of joint action (for a review, see Ref. 54), in
which individuals coordinate their actions in order
to accomplish joint physical or communicative
goals. Before 1 year of age, parents and infants are
already engaging in joint action, and the amount of
coordinat ion between moth ers and infants at 3 a nd 9
months of age predicts infant self-regulation and fu-
ture IQ and empathy.55 With respect to music, infant
head, body, hand, and leg movements are most syn-
chronized to their mother’s singing at the begin-
nings and ends of musical phrases,56 suggesting the
presence of a precursor to entrainment.
47
Ann. N.Y. Acad. Sci. 1337 (2015) 45–52 C⃝2014 New York Academy of Sciences.
Interpersonal synchrony and social development Trainor & Cirelli
Another important ingredient in early social cog-
nition is joint attention, the ability to coordinate
attention with a social partner in order to inform
and share experiences.57 As young as 12 months
of age, for example, infants (unlike chimpanzees)
will initiate joint attention by pointing to objects
in order to get others to attend to them.58,59 At
even younger ages, infants show preferences for
other people who exhibit certain behaviors such as
smiling60–62 and making direct eye contact.63 Inf-
ants also show preferences for others who are similar
to themselves.64 Furthermore, young infants under-
stand social agents as having intentional goals. In-
fants 6 to 10 months of age approach objects that
have helped another object and avoid those that have
hindered another object from achieving a goal.65
Furthermore, 3-month-olds look longer at an ob-
ject previously seen to help another object climb a
hill compared to an object previously seen to hinder
another object from climbing the hill.66
Instrumental helping behaviors, an early mani-
festation of altruism, emerge before 18 months of
age.67,68 Infants as young as 14 months can recog-
nize the goal of another person and spontaneously
help them to achieve this goal without any reward.
Specifically,in one study, 14-month-old infants were
shown to help adults by giving them out-of-reach
objects needed for the adult to achieve a goal; for
example, during a task in which the adult was pin-
ning towels on a clothesline, when the adult “acci-
dentally” dropped a clothespin, the infants picked
it up and handed it back to the adult more often
than when the adult purposely dropped the
clothespin.69 In sum, the basic elements of social
cognition and proso cial behavior are present in infa-
nts by 14 months of age. Together with their abil-
ity to perceive the meters of auditory rhythms and
the existence of connections between auditory and
motor domains for rhythm, as reviewed above, it is
reasonable to ask whether synchronous movement
between a 14-month-old infant and an adult would
lead to increases in prosocial behavior in the infant
as it does in adults.
Interpersonal synchrony and prosocial
behavior in infancy
In a series of studies we have tested whether the
experience of interpersonal synchrony in a musical
context leads to increased altruistic behaviors in 14-
month-old infants.70,71 The basic design included an
interpersonal movement phase followed by a proso-
cial test phase. During the interpersonal movement
phase, an assistant stood and held the infant in a
forward-facing carrier such that the infant faced
an experimenter. The infant listened to “Twist and
Shout” by The Beatles over speakers for 145 seconds.
The assistant and experimenter listened to sepa-
rate beat tracks over headphones, which instructed
them on how to bounce. The synchrony of bouncing
between the experimenter and infant was the ma-
nipulation of interest. During synchronous bounc-
ing conditions, the beat tracks of the assistant and
experimenter matched, and they bounced to the
tempo of the music. In the original study, dur-
ing asynchronous bouncing conditions, the exper-
imenter bounced either 33% slower or faster than
the infant. In addition, during antiphase bouncing
conditions, the infant and experimenter bounced at
the same tempo, but the highest and lowest points
of their movement trajectories occurred at opposite
times. Both the assistant and the experimenter wore
Nintendo Wii remotes to measure their movement
trajectories, and the experimenter was videotaped
in order to ensure that her behavior was consistent
across conditions.
During the prosocial test phase, infants com-
pleted instrumental helping tasks based on those
of Warneken and Tomasello.69 For example, during
the paper ball task, the experimenter picks up pa-
per balls with tongs and places them in a bucket
and tries to get paper balls that are out of reach.
During the marker task, the experimenter draws a
picture and “accidentally” drops a marker off the
table and out of reach. During the clothespin task,
the experimenter “accidentally” drops a clothespin
out of reach while attempting to clip up dishcloths
on a clothesline. For each task, the trial begins when
the object is dropped and/or signaled to be out of
reach. For the first 10 s, the experimenter gazes at
the object. For the next 10 s, she alternates look-
ing at the infant and the object, and for the last
10 s, she adds vocalization (e.g., “my marker!”). Tri-
als ended when the infant picked up and returned
the object or after 30 seconds. The experimenter was
videotaped in order to ensure that her behavior was
consistent across conditions.
The initial study found that infants helped the
experimenter significantly more if they had bounced
to music in synchrony with her compared to if
they had bounced out of sync.70 Analyses of the
48 Ann. N.Y. Acad. Sci. 1337 (2015) 45–52 C⃝2014 New York Academy of Sciences.
Tra i n o r & Cir e l li In t e r per s o n a l syn c h ron y a n d s oci a l d e v elo p m e nt
movement trajectory data during bouncing revealed
no systematic differences in individual bouncing
across conditions, and adults who rated video clips
of the experimenter during both phases of the
experiment were unable to detect any differences
across conditions, including in bouncing quality,
happiness displayed by the experimenter, and ex-
perimenter interaction during the helping tasks.
These analyses indicate that the experiment was well
controlled. Thus, remarkably, less than 3 min of
synchronous movement experience can increase in-
fants’ prosocial behavior. Interestingly, the increase
in helping occurred primarily during the first 10 s,
suggesting that it was spontaneous in nature.
Delayed helping, defined as occurring after the
first 10 s and potentially reflecting compliance, was
significantly related to personality variables as mea-
sured by the Infant Behavior Questionnaire, in-
cluding dispositional positivity and willingness to
approach novel objects,72 whereas spontaneous
helping during the first 10 s was not.
Afollow-upexperimentshowedthatantiphase
bouncing also subsequently increased spontaneous
helping in 14-month-old infants when compared to
asynchronous bouncing.70 This indicates that iden-
tical movements are not necessary for this social
effect but that the tempo of the oscillatory move-
ment may be critical. This is consistent with a study
of dancing in adults, which found that dancers who
made synchronously timed but not necessarily iden-
tical movements were subsequently able to remem-
ber more information about each other compared
to dancers who moved at different tempi.14 It is also
possible that antiphase movement, in particular, is
privileged, and there is a rich literature on its sta-
bility in adults.29,30 Future studies could disentangle
effects of phase and movement similarity.
One important question is whether infants’ expe-
rience of synchronous movement is pleasurable and
causes them to be generally more helpful (i.e., acts
as a social prime) or whether the effect is targeted
at the person with whom they experienced the syn-
chrony (i.e., acts as a social cue). We reran the initial
experiment described above but with a nonbounc-
ing neutral stranger present in the room during the
interpersonal movement phase.71 As in the initial
experiment, infants bounced either in sync or out
of sync with the experimenter. During the proso-
cial test phase, we measured infants’ willingness to
help both the experimenter and the neutral stranger.
With the experimenter, we replicated the effect of
synchronous movement experience: infants who
bounced in synchrony with the experimenter were
subsequently more likely to help the experimenter
compared to infants who bounced out of sync. How-
ever, there was no effect of bouncing condition
on helpfulness toward the neutral stranger. Thus,
prosocial consequences of synchronous movement
experience are targeted at the person with whom the
movement was experienced.
Music making often involves groups of people,
and, indeed, it has been suggested that music
making increases within-group cohesion.73 The
specificity of prosocial consequences of syn-
chronous movement can be investigated further
by examining whether infants display increased
helpfulness toward friends (positive affiliates) of
a synchronous bouncing partner but not toward
neutral affiliates. In a recent study we had infants
initially watch the experimenter interacting with
a second experimenter.74 In the positive experi-
menter affiliation condition, the two experimenters
engaged in similar gestures and solved a problem
together. In the neutral experimenter affiliation
condition, the two experimenters engaged in similar
actions but did not interact. The results revealed
that if the infant bounced synchronously with one
of these experimenters, he or she showed increased
helping toward the second experimenter if she or
he were in the positive experimenter affiliation
condition but not if she or he were in the neutral
experimenter affiliation condition, and there were
no effects if the infant bounced asynchronously
with the experimenter. Thus, the prosocial effect
of synchronous movement extends to third parties
who are in the same social group.
Conclusions and future directions
The studies presented here indicate that syn-
chronous movement to music has immediate and
powerful prosocial effects, increasing altruistic
behaviors in infants as young as 14 months.
Furthermore, these altruistic effects are targeted at
synchronously moving partners and their positive
affiliates. Infants younger than 14 months do not
readily engage in helping behaviors. However, they
still form expectations about social behaviors, pre-
ferring, for example, those who are attractive,75 use
infant-directed speech,76 and engage in prosocial
behavior.65,77,78 Thus, we are currently exploring
49
Ann. N.Y. Acad. Sci. 1337 (2015) 45–52 C⃝2014 New York Academy of Sciences.
Interpersonal synchrony and social development Trainor & Cirelli
the possibility that during the first year after birth,
infants expect synchronously moving partners to
engage in prosocial behaviors to a greater extent
than asynchronously moving partners. In general,
the findings to date suggest that interaction through
movement and music is an important tool in early
social development.
Acknowledgments
The writing of this paper was supported by grants
from the Canadian Institutes of Health Research
and the Natural Sciences and Engineering Research
Council of Canada. Thanks to Susan Marsh-Rollo
for assistance preparing the manuscript.
Conflicts of interest
The authors declare no conflicts of interest.
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