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- mise à jour
du
- 16 mars
2025
- Human
Nature
- 2025
March 13
|
- Is it a
Match?
- Yawn
Contagion and Smile Mimicry in
Toddlers
- Ivan Norscia, Marta Caselli, Chiara
Scianna,
- Sara Morone, Martina Brescini, Giada Cordoni
-
- Department of Life
Sciences and Systems Biology, University of
Torino
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- Tous
les articles sur la contagion du
bâillement
- All
articles about contagious
yawning
-
- Abstract
- Automatic behavioral matching includes Rapid
Facial Mimicry (RFM) and Yawn Contagion (YC)
that occur when the facial expression of an
individual acts as a 'mirror social releaser'
and induces the same facial expression in the
observer (within 1 s for RFM, and minutes for
YC). Motor replication has been linked to
coordination and emotional contagion, a basic
form of empathy. The authors investigated the
presence and modulating factors of Rapid Smile
Mimicry (RSM) and YC in infants/toddlers from 10
to 36 months at the nursery 'Melis' (Turin,
Italy). In February-May 2022, they gathered
audio and/or video of all occurrences data on
affiliative behaviors, smiling during play, and
yawning during everyday activities. Both RSM and
YC were present, as toddlers were most likely to
smile (within 1 s) or yawn (within three-min)
after perceiving a smile/yawn from another
toddler. Sex, age, and parents' country of
origin did not influence RSM and YC occurrence,
probably because gonadal maturation was long to
come, the age range was skewed towards the early
developmental phase, and toddlers had been in
the same social group for months. RSM and YC
showed social modulation, thus possibly implying
more than just motor resonance. Both phenomena
were inversely related to affiliation levels (a
social bond proxy). Because literature reports
that in adults RSM and YC may increase with
familiarity, our reversed result suggests that
in certain toddler cohorts the same phenomena
may help increase socio-emotional coordination
and that the function of motoric resonance may
be experience- and context-dependent.
-
- Résumé
- L'appariement comportemental automatique
comprend le mimétisme facial rapide (RFM)
et la contagion du bâillement (YC) qui se
produisent lorsque l'expression faciale d'un
individu agit comme un « miroir social
» et induit la même expression
faciale chez l'observateur (dans un délai
d'une seconde pour le RFM, et de quelques
minutes pour le YC). La réplication
motrice a été associée
à la coordination et à la
contagion émotionnelle, une forme
fondamentale d'empathie. Les auteurs ont
étudié la présence et les
facteurs modulateurs de la mimique rapide du
sourire (RFM) et de la YC chez les nourrissons
et les tout-petits âgés de 10
à 36 mois à la crèche
« Melis » (Turin, Italie). Entre
février et mai 2022, ils ont recueilli
des données audio et/ou vidéo sur
toutes les occurrences de comportements
affiliatifs, de sourires pendant le jeu et de
bâillements pendant les activités
quotidiennes. Le RSM et le YC étaient
tous deux présents, car les tout-petits
étaient plus susceptibles de sourire
(dans un délai d'une seconde) ou de
bâiller (dans un délai de trois
minutes) après avoir perçu un
sourire/un bâillement d'un autre
tout-petit. Le sexe, l'âge et le pays
d'origine des parents n'ont pas eu d'influence
sur l'apparition de RSM et de YC, probablement
parce que la maturation gonadique était
décalée, que la tranche
d'âge était biaisée en
faveur de la phase de développement
précoce et que les tout-petits avaient
été dans le même groupe
social pendant des mois. Le RSM et le YC ont
montré une modulation sociale, ce qui
implique peut-être plus qu'une simple
résonance motrice. Les deux
phénomènes étaient
inversement liés aux niveaux
d'affiliation (une approximation du lien
social).
-
- Introduction
- Behavioral matching is a form of motor
replication that takes place when an observed
behavior induces the observer to repeat it
(Gallese, 2004; Schütz-Bos- bach &
Prinz, 2015; Zentall, 2003). Behavioral matching
can occur at diGerent cognitive levels ranging
from automatically mirroring others' motor
patterns to 'copying' phenomena that require
high-level cognitive appraisal (e.g., true imi-
tation, emulation; Zentall, 2012). Depending on
cognitive complexity and self- other distinction
abilities, behavioral matching can have diGerent
social repercus- sions, such as emotional
transfer, social learning facilitation, and
promotion of social relations by fostering
amliation and cooperation (Berthier &
Semple, 2018; Canteloup et al., 2020; de Waal
& Preston, 2017; Panksepp & Panksepp,
2013; Paukner et al., 2009).
- The most basic level of behavioral matching
is automatic motor replication, a broad umbrella
concept that includes motor mimicry and
behavioral contagion (Palagi et al., 2020),
because both can be mediated by the
Perception&endash;Action Model (PAM) and the
Mirror Neuron System (MNS; de Waal &
Preston, 2017; Rizzolatti & Caruana, 2017).
According to PAM and MNS, for both phenom- ena
the observation of the motor pattern activates
in the observer the same motor neurons as in the
individual performing such a pattern, with the
focus being on the goal more than on the action
(MNS; Rizzolatti & Caruana, 2017; Rizzolatti
& Fabbri-Destro, 2010; Schütz-Bosbach
& Prinz, 2015) and with the observer's
response being shaped by their own experience
(PAM; Preston & de Waal, 2017). However,
motor mimicry diGers from behavioral contagion
because the former involves the observer
repeating others' motor patterns within a short
time win- dow (within 1 s or a few seconds),
whereas the latter involves the observer rep-
licating the behavior but not necessarily the
exact actions of others over longer time windows
(ranging from less than 1 s to several minutes;
Palagi et al., 2020; Prochazkova & Kret,
2017; Wheeler, 1966; Zentall, 2003). Depending
on the behavior being considered, behavioral
contagion can also involve a physiological
component, which may account for the delayed
response often observed in con- tagion compared
to pure mimicry (Prochazkova & Kret, 2017).
In both cases, the behavioral pattern performed
by an individual and perceived by another
individ- ual (via vision or other sensory cues)
works as a 'social releaser' (sensu Tinber- gen,
1951). According to Konrad (1935), social
relations are dependent on a wide array of
stimuli emitted by one individual (the "actor")
that release responses in another individual
(the "reactor"). Based on this, Tinbergen (1948,
1951) showed that innate social responses are
dependent on the display of releasers and better
defined the social dimensions of releasers. In
the case of automatic motor repli- cation,
others' motor patterns not only act as social
releasers (sensu Tinbergen, 1951) but generate
in the perceiver a specific 'mirror response'.
Motor mimicry and contagion can occur with
diGerent 'mirror social releasers', as we may
define them, and translate the motor pattern
from the individual to the social level.
-
- A form of motor mimicry is Rapid Facial
Mimicry (RFM), where the facial expression
displayed by an individual (e.g., smile in Rapid
Smile Mimicry, RSM) induces the observer to
reproduce the same expression within 1 s (de
Waal & Preston, 2017; Iacoboni, 2009; Palagi
et al., 2020; Schütz-Bosbach & Prinz,
2015; Zentall, 2003). A form of behavioral
contagion is yawn contagion, which occurs when a
perceived yawn triggers a yawning response in
the perceiver (Pro- vine, 1989a, 1989b). Such a
response can be within 1 s, a few seconds, or
even minutes from the exposure to the yawning
stimulus (Palagi et al., 2020; Provine, 2005).
The relevance of investigating facial mimicry
and yawn contagion is that they may be related
to emotional contagion, an automatic and
implicit form of empathy (Preston & de Waal,
2002, 2017). It has been hypothesized that auto-
matic motor replication via facial mimicry and
yawn contagion may have func- tioned as an
exaptation for emotional contagion (Hess &
Fischer, 2013; Palagi et al., 2020). By
observing the facial expression of another
person, the observer may activate not only the
motor neurons connected with the expression but
also shared representations of the emotion that
such expression conveys (de Waal & Preston,
2017).
-
- In infants and toddlers, smiling is
considered the expression of positive emotions
(Messinger et al., 2008). Smiles can involve a
wide combination of diGerent facial unit
movements, but four main types may be recognized
based on mouth open- ing and eye-constriction:
simple/basic smile (mouth closed/no eye
constriction), play smile (mouth open, no eye
constriction), Duchenne smile (mouth closed/eye
constriction), and duplay smile (mouth open/eye
constriction; Fogel et al., 2006; Messinger et
al., 2008). Although play smiles are the most
common during play (as the name indicates), the
other types of smiles can be variably present
during this behavior (Dickson et al., 1997;
Fogel et al., 2006). Hence, social play is one
of the most suitable behaviors to consider when
investigating facial mimicry, as play ses- sions
are visually punctuated by smiles.
-
- Rapid facial mimicry of playful facial
expressions may be biologically ancient as it
has been observed in humans (Seibt et al.,
2015), other hominids (orangutans&emdash; Pongo
pygmaeur: Davila-Ross et al., 2008; chimpanzees
&endash; Pan troglodyter&emdash;and gorillas
&endash; Gorilla gorilla: Palagi et al., 2019;
bonobos &endash; Pan panircur: Bertini et al.,
2022), and other animal species (spanning
monkeys, rodents and carnivores; Pal- agi et
al., 2020), where they are termed 'play faces'
or 'relaxed-open mouth'. This observation
suggests deep mammalian roots of the phenomenon.
Automatic facial expression replication (not
necessarily related to true imitation),
including smile, is observed since the first
phases of life in human infants (but also
non-human pri- mates; Ferrari et al., 2006;
Jones, 2009; Wörmann et al., 2014).
Automatic facial mimicry in humans appears to be
present as early as 5 months of age, when mul-
timodal emotional stimuli are elaborated
(Isomura & Nakano, 2016). Smile mim- icry
has been described in adult humans as well
(e.g., Mui et al., 2018; Seibt et al., 2015).
Individual and social factors may influence
facial mimicry, such as age, sex, group
membership, and social bond (Seibt et al.,
2015). Facial emotion recogni- tion skills
change with age (e.g., in relation to
sensitivity to diGerent emotions or increase of
finely tuned discrimination abilities) and as
early as in the first two years of life
cognitive and mimicking abilities of toddlers
increase in variety, latency, and complexity
(Grossman et al., 2007; Hühnel et al.,
2014; Jones, 2009; Lawrence et al., 2015).
Hence, this can potentially aGect the extent to
which facial mimicry is expressed&emdash;as age
increases&emdash;during naturally occurring
social interactions. Moreo- ver, human females
show possibly more precise and/or effective
processing of emo- tional facial expressions and
increased facial mimicry than men, as a result
of pos- sible inter-sex diGerences in the smile
facial mimicry neural network (Dimberg &
Lundquist, 1990; Hall, 1978; Hall &
Matsumoto, 2004; HoGmann et al., 2010; Korb et
al., 2015). Additionally, group
membership&emdash;including country of origin
and eth- nicity&emdash;can influence the amount
of mimicry response to others' facial
expressions (also according to type, e.g., happy
vr angry) in young children and adults (de Klerk
et al., 2019; Rauchbauer et al., 2016; Seibt et
al., 2015). Finally, facial mimicry can be
influenced by diGerent social setting variables,
including the social relationship between
interactants. Although few studies have
investigated this aspect, facial mim-
icry&emdash;including smile mimicry&emdash;may
increase when the social bond is tight (Fis-
cher et al., 2012; Häfner & Ijzerman,
2011).
-
- Although understudied, a modulation of
individual factors on the rapid facial mimicry
of the play face has been observed in non-human
primates, including homi- nid species (e.g., sex
combination of interactants, lowland gorillas:
Bresciani et al., 2022; age, orangutans:
Davila-Ross et al., 2008). Moreover, a positive
influence of the social relationship on play
face facial mimicry rates has been found in non-
human mammals, such as dogs (Palagi et al.,
2015). Thus, the modulation of rapid facial
mimicry of smile may be rooted in mammalian
evolution and vary depending on species
biology.
-
- Contrary to smile, yawning can be associated
with physiological transitions (e.g., from sleep
to wake) and also neffative internal states,
such as boredom, tiredness, or mild stress
(Guggisberg et al., 2010; Thompson, 2014; Zilli
et al., 2007). The yawn- ing-like motor pattern
is likely a plesiomorphic display as it has been
described in a wide range of vertebrates,
including non-human primates (Anderson, 2020;
Baen- ninger, 1997). Besides humans (Provine,
1989a, 1989b), yawn contagion has been reported
in a variety of animal species (mammals, for
review: Palagi et al., 2020; bird: Meloprittacur
undulatur; Gallup et al., 2015), including
hominids (e.g., oran- gutans: van Berlo et al.,
2020; chimpanzees: Anderson et al., 2004;
bonobo: Demuru & Palagi, 2012; but not
gorillas: Palagi et al., 2019). Thus, yawn
contagion, as facial mimicry, might stem from
ancient evolutionary foundations, although the
variation in the reported expression of the
phenomenon may relate to species-specific social
features more than to phylogeny, and/or to
sample limitations (Palagi et al., 2020; van
Berlo et al., 2020).
-
- As facial mimicry, in humans also yawn
contagion can be aGected by individ- ual and
social factors. The influence of sex on yawn
contagion rates is still under debate as it was
found in certain cohorts of adult humans (with
females showing more contagion, e.g., Chan &
Tseng, 2017; Norscia et al., 2016) but not in
others (e.g., Bartholomew & Cirulli, 2014;
Norscia & Palagi, 2011), with cultural
features possibly enhancing variability (Palagi
et al., 2020). No sex effect on yawn contagion
was found in children from 2.5 to 5.5 years old
(Cordoni et al., 2021). Contrary to sex, age is
a critical variable influencing yawn contagion.
As a matter of fact, yawn contagion increases
during ontogenetic development, with children by
the age of 10&endash;11 years showing contagion
levels similar to adults (Anderson & Meno,
2003). Previous reports that used yawn video
stimuli found that infants and toddlers (6 to 34
months old) did not respond to their mothers'
yawns from 6 to 34 months old (Miller and
Anderson, 2011) or others' yawns up to 5 years
old (Anderson & Meno, 2003). Helt et al.
(2010)&emdash;by exposing children to real yawns
emitted by a live, adult subject&emdash;found
that yawn contagion increased with age from 1 to
5&endash;6 years old, being virtually absent
between 1 and 2 years of age (0&endash;5% of
toddlers show- ing a yawn response at least in
one trial) and still infrequent by the age of 3
(10% of toddlers responding). An increase to
35&endash;40% was observed in children from 4 to
5&endash;6 years old. However, no analysis is
available on the presence or absence of the
phenomenon at the group level for diGerent age
classes. A study investigating yawn contagion in
a naturalistic social setting, during children's
everyday activities in a nursery, found that
yawn contagion was already present at 2.5 years
of age (Cordoni et al., 2021). The study did not
investigate the possible presence of yawn
contagion before that age as younger toddlers
were not present in the sample. Finally, litera-
ture on adults shows that country of origin
diGerences may not aGect yawn conta- gion
whereas stronger social relationships between
individuals increase yawn con- tagion
probability in certain human cohorts (Norscia
& Palagi, 2011; Norscia et al., 2020, 2021).
Although this aspect is not known in children,
such an effect cannot be excluded during the
first phases of ontogeny, as the intersubjective
ability to diGer- ently respond to others'
emotional expressions depending on familiarity
appear early in infant development
(Walker-Andrews et al., 2011).
-
- The effect of individual (i.e., sex and age)
and social factors (i.e., group member- ship
and/or familiarity) in modulating the expression
of yawn contagion may also be biologically
rooted in human evolutionary history, as they
can variably aGect yawn contagion in non-human
animals, including non-human hominins
(chimpanzees and bonobos; e.g. Campbell & de
Waal, 2011; Demuru & Palagi, 2012; Madsen et
al., 2013; Massen et al., 2012; Norscia et al.,
2022). In particular, social modulation may
indicate that yawn contagion is not merely a
phenomenon of motoric resonance (in which case
it would be equally distributed across dyads)
but that it may underlie an emotional transfer
component (Norscia et al., 2021; Palagi et al.,
2020; but see: Massen & Gallup, 2017).
-
- In this study, we report for the first time
on the presence and modulating factors of rapid
facial mimicry and yawn contagion, as a possible
proxy of emotional conta- gion, in early and
late toddlers (from 10- to 36-month-old), mostly
below 2.5 years of age. Based on the above
framework, we put forth the following
predictions.
-
- Discussion
- Our results indicate that motor replication
can be present in toddlers for both Rapid Smile
Mimicry (RSM; Prediction 1a supported) and Yawn
Contagion (YC; Predic- tion 2a supported).
EFFect sizes (Table 2 and 3) are not large but
correspond to odds ratios (1.30&endash;1.65)
that are practically significant. The presence
of RSM and YC in young toddlers is consistent
with previous reports indicating that facial
mimicry in humans appears in the first months of
age (Ferrari et al., 2013; Isomura & Nakano,
2016). The emergence of motor replication in
pre-verbal toddlers aligns with the observation
that rapid facial mimicry and yawn contagion are
rooted in human biol- ogy and anchored to the
non-verbal domain, as they are also found in
non-human mammals, including primates and
particularly hominids (e.g. Anderson et al.,
2020; Davila-Ross et al., 2008; Demuru &
Palagi, 2012; Norscia et al., 2022; Palagi et
al., 2019; Palagi et al., 2020; van Berlo et
al., 2020; but see Palagi et al., 2019). Facial
expressions can convey emotional cues and the
ability to gain emotional informa- tion from
others' bodily and facial movements is
primordial to survival (Heck et al., 2018).
Indeed, emotion detection (for neffative and
positive emotions) involves a neural network
that includes evolutionarily conserved brain
areas such as the amyg- daloid complex, in
humans, non-human primates and other animals
(Ferretti & Papaleo, 2019; Pabba, 2013).
Motor resonance and the possibly related
emotional sharing (a foundation of empathy) are
drivers of prosocial behaviors in humans and
other animals (Decety et al., 2016). Indeed,
children that are better able to spot and share
the expressions of their peers can be more
prosocially responsive to their peers (Denham et
al., 2003). In humans and other hominids,
coordination of behaviors and internal states
allows social interactions to successfully
continue at the dyadic level and the achievement
of collective goals at the group level (Nowak et
al., 2017; Pal- agi et al., 2020; Parr et al.,
2005). Focusing more specifically on yawn
contagion, its presence also below two years
indicates that this type of motor resonance
emerges earlier in human development than
previously described. Cordoni et al. (2021)
pointed out that the naturalistic setting, and
exposure to spontaneous, real yawns (rather
video or faked stimuli) from peers belonging to
the same group (rather than adults and/or
unfamiliar subjects) allows the early detection
of motor resonance. Such conditions may indeed
increase signal effectiveness, reduce response
inhibi- tion and/or enhance the motoric
response.
-
- As concerns the modulating factor of rapid
facial mimicry and yawn contagion, for neither
phenomenon we found an effect of sex (as
expected; Prediction 1c and 2c, for RSM and YC
respectively, supported), age (contrary to
expectations; Predic- tion 1b and 1c for RSM and
YC respectively, not supported), and parents'
country of origin (the predictions diverged for
RSM and YC, with an effect expected only for
RSM; Prediction 1d on RSM not supported;
Prediction 2d on YC supported). Reffarding age,
it is possible that the short age span of our
toddlers&emdash;with age increasing by the
month&emdash;has dampened the effect of
age-related variations. It is also possible that
in the early ontogenetic stages covered by this
study, such varia- tion has not yet emerged.
Indeed, important changes in replication
modulation abili- ties may emerge in toddlers at
later stages and, for example for yawn
contagion, a conspicuous increase probably
starts occurring after 5 years of age (Anderson
& Meno, 2003; Cordoni et al., 2021; Helt et
al., 2010; Jones, 2009).
-
- Reffarding the geographical origin, the lack
of an appreciable effect on both RSM and YC may
be because the toddlers were born in the same
country (although some of the parents had
immigrated from abroad), they knew each other
since at least 4&endash;5 months, and belonged
to the same class, hence to the same social
group. Although an ethnic bias in facial
recognition may exist and decrease with age,
there is evidence that overall visual attention
may not diGer as a function of ethnicity, that
happy faces are better identified across ethnic
groups and that humans from diGer- ent ethnic
background can overcome such bias when they live
together for a period of time (Kawakami et al.,
2014; Michel et al., 2006; Seffal et al., 2019).
Reffarding sex, the early stage of
developments&emdash;far from gonadal maturation
and related mor- phophysiological
changes&emdash;may account for the lack of sex
diGerences, which are instead observed later in
life for facial mimicry (e.g., Dimberg &
Lundquist, 1990) and yawn contagion (e.g., Chan
& Tseng, 2017) at least in certain human
cohorts. This is also consistent with the lack
of sex effect on yawn contagion in children from
2.5 to 5.5 years old (Cordoni et al., 2021). It
is interesting to notice, however, that in the
control model on the individual factors
modulating yawning (to be considered in this
case as spontaneous as untriggered by previous
yawns from others), the yawner sex had a
significant effect, with males yawning more than
females. Similarly, Cor- doni et al. (2021)
found that male children yawned more than female
children under naturalistic conditions, possibly
due to androgens, which are known to increase
yawning in mammals (Cordoni et al., 2021; Graves
& Wallen, 2006; Homgren et al.,
- 1980; Melis et al., 1994; Rodriguez-Sierra
et al., 1981) and can already have an effect in
perinatal phases (Alexander, 2014; Vigil et al.,
2016). The increased yawn levels in males may
also be linked to stress-induced aggression and
higher cortisol levels (Cordoni et al., 2021;
Thompson, 2014), as male infants can be more
easily aroused by stressors under certain
conditions (Richardson et al., 2010). Further
stud- ies are needed to investigate this, as sex
effects on spontaneous yawning in infants may
vary with external stimuli (e.g., Menin et al.,
2022 found increased yawning in infant females).
It is essential to replicate this study across
various toddler cohorts to see if the observed
lack of RSM and YC modulation in relation to
individual factors holds true at the population
level for the age span considered here, or if
variations may emerge based on age, sex, and
geographic origin composition.
-
- Finally, the amliation level (a proxy for
social bond) had an effect on both RSM and YC.
EFFect sizes (Table 2 and 3) are good and
correspond to odds ratios that are practically
significant (1.51&endash;1.97). Our result is in
line with the observation that the ability to
diGerently respond to others' emotional
expressions depending on the level of attachment
(i.e., familiarity) appears early in the
development of infant (Walker- Andrews et al.,
2011), along with the ability to distinguish
emotional facial expres- sions emerges
(5&endash;7 months of age; Cruz et al., 2023;
Flom & Bahrick, 2007). How- ever, the most
intriguing result is that the observed effect of
amliation levels was not in the expected
direction (Prediction 1e and 2e for RSM and YC
respectively, not supported). While in certain
cohorts of human adults both RFM and YC can
increase when the social bond is tighter (e.g.,
Fischer et al., 2012; Häfner & Ijzer-
man, 2011; Norscia & Palagi, 2011), in our
toddler cohort we observed an oppo- site effect.
Specifically, RSM and YC were highest between
toddlers sharing least amliation. The social
asymmetry in the levels of RSM and YC across
dyads may indicate that they do not merely
involve motoric resonance and that internal
states may be also involved, depending on the
experience that is shared with them (as pre-
dicted by the Perception&endash;Action Model, de
Waal & Preston, 2017). When the rela- tion
between motor resonance and social bond is
positive (the former increases as the latter
increase), it has been hypothesized that motoric
resonance may be cou- pled with a basic form of
empathy, as the positive association mirrors the
so-called 'empathic trend' (Palagi et al., 2020;
de Waal & Preston, 2017; but see: Massen
& Gallup, 2017). Instead, when the relation
between motor replication phenomena and social
bond is not positive, but as in our case
neffative, the link between motoric resonance
and emotional contagion must be interpreted
within a broader framework. Even though accounts
are scarce at the moment, there is evidence that
in non-human hominids motor replication can have
a neffative relation with amliation levels. As a
matter of fact, this trend has been observed for
example in young gorillas for RFM (Bresciani et
al., 2022) and in bonobos for yawn contagion (De
Vittoris et al., 2024). The variable association
between motor replication and amliation levels
may be rooted in human biological history. The
amygdala, an evolutionarily conserved brain
area, in humans encodes episodic memory and
subjective evaluation of emotional faces rather
than just visual elements (Dolcos et al., 2004;
Wang et al., 2014). This is an adaptive feature,
as natural selection favors responses that are
most suitable to individuals in the environment
where they interact. Indeed, environment modu-
lates such responses (Bijlsma & Loeschcke,
2005). Facial expression phenotypes and
functions are connected to socio-ecological
context (social intelligence hypoth- esis;
Schmidt & Cohn, 2001). In humans, contextual
factors may influence how social factors
modulate facial expression replication (Seibt et
al., 2015), and con- text variety and social
information complexity can obscure emotional
cues from facial movements (Barrett et al.,
2019). Context can also determine the emotional
nuance of expressions and the corresponding
response, as valence is not always entirely
evident (Kret & Akyuz, 2022). Yawning in
humans may be associated for example with
testosterone (anger), cortisol (distress) but
also with neutral behav- ioral transitions
related to the circadian rhythm (e.g., Cordoni
et al., 2021; Thomp- son, 2014; Zilli et al.,
2007). Smile is more widely associated with
happiness but in both adult humans and children
it may be expressed out of frustration or in
social exclusion situations (incongruent aGect;
Mateo Santana & Grabell, 2023; Svetieva et
al., 2019). Young children are still in the
process of building their competence in the
finely tuned detection of emotions in others'
facial expressions, which is impor- tant for
effective socio-emotional communication (Dehnam,
2018). The young chil- dren under study included
infants and early toddlers with still scarce
experience in emotionally interacting with
others in a group social setting. Both
inexperience and complex social situations may
have contributed to shaping their response to
the facial expressions of group mates in
relation to amliation. Motor replication, cou-
pled with emotional state replication, may
function in reducing the prediction error over
others' behavior, thus leading to appropriate
decision making (Kret & Akyuz, 2022). The
decision-making process, in humans, also
involves subcortical brain areas (Prochazkova
& Kret, 2017). The reduction of the
prediction error may lead to at least to two
opposite outcomes (and of course a range of
possibilities in-between). On one extreme, such
reduction may be pivotal to the continuation of
social inter- action via coordination, as the
prediction error is probably highest between
less familiar individuals. This may help develop
social bonds with less known individu- als (De
Vittoris et al., 2024). Depending on the
circumstances, however, the error reduction may
also serve to interrupt, rather than facilitate,
an interaction (Kret & Akyuz, 2022; Diana
& Kret, 2025). In humans, for example,
mimicry can lead to lower levels of trust (Diana
et al., 2023) and yawn can mark behavioral
transitions, which involve the interruption of
one activity to commence another (e.g., resting
to moving, sleep to wake; Gallup, 2022; Zannella
et al., 2015). Based on the above elements, it
is possible to point out that the social
asymmetry of motor replication in relation to
amliation observed in toddlers suggests that
internal states may be also involved in such
replication. The type of emotional connection
that is established via mirror social releasers
can depend&emdash;especially in
toddlers&emdash;on the stage of develop- ment of
individual competence and various contextual
variables, such as group com- position and
situational aspects. This kind of modulation
emerges early in ontogeny and is probably
evolutionary ancient, for the reasons explained
above.
-
- This study can lay the groundwork for deeper
investigation in various comple- mentary
directions. In order to do that, because young
toddlers socially play at lower frequencies than
older ones, larger datasets are necessary. For
example, future work may consider the possible
laterality of emotional facial expressions (e.g.
Mandal and Ambady, 2004) and whether mimicry is
(or not) axially specific, as these aspects may
also modulate the response. The combined effect
of RSM and YC on amliation levels may also be
considered, as long with the effect of the
mimicry of diGerent types of smiles, here
conflated into a single cateffory. A point of
reflection concerns the fact that in a
naturalistic context it was not possible to
measure eye contact, which is a factor known to
potentially influence facial mimicry,
particularly in the context of smile mimicry
(Mauersberger et al., 2022). However, this study
has the merit of considering mimicry in its
naturally occurring social context, and in this
respect, our results can add to the results
obtained by using eye-tracking techniques.
Future studies should explore the effect that
mimicry has on play sessions (e.g., duration,
patterns used) to highlight possible
repercussions on social bonding. Moreover, the
inclusion of other human cohorts (at early and
later developmental stages) and the adoption of
comparative approach with other primates
(especially hominids) would be welcome in future
investigation, to delve further into the
ontogenetic and evo- lutionary basis of facial
mimicry. Finally, in this study, we specifically
focused on smile mimicry and contagious yawning,
but other potential dynamics between dyads are
likely to exist, such as mimicry of diGerent
facial expressions or behaviors. This aspect is
worth considering in future investigations,
possibly on a larger dataset.
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