The e ec o social se ings
and ol ac o y en i onmen s on
spon aneous mo emen synch ony
M. R. Coeugne 1, Y. N. Dele oye-Tu ell 1,2,5, W. Tschache 3 & J. Cou inho 4
In e pe sonal synch ony e e s o he empo al coo dina ion be ween wo indi iduals, signaling
he coupling o hei beha io s. Op imal mo emen synch ony in dyads is linked o mo e a ilia i e
beha io , coope a ion, and us . Howe e , he e is limi ed esea ch on how he senso y en i onmen
impac s in e pe sonal synch ony. One signi ican en i onmen al ac o in luencing human beha io
and social in e ac ions is ambien odo s. This s udy aimed o examine he e ec o ambien odo on
in e pe sonal synch ony, pa icula ly in-phase mo emen synch ony. Mo ion ene gy analysis and
windowed c oss-co ela ions we e used o measu e synch ony le els be ween pa icipan s du ing
ideo- eco ded in e ac ions. Twen y- i e same-sex iend dyads pe o med h ee in e ac ion asks
designed o c ea e un, coope a i e, o compe i i e a mosphe es. These asks we e conduc ed wi h a
pleasan , s imula ing peppe min odo o in a con ol condi ion wi hou odo . Consis en wi h p e ious
s udies, highe synch ony le els we e obse ed in un a mosphe es compa ed o compe i i e and
coope a i e ones. No signi ican e ec s o odo s imula ion we e ound. O e all, he esul s con i m
ha social con ex signi ican ly in luences mo emen synch ony and a ilia ion, while ambien odo
migh no a ec in e pe sonal synch ony, a leas when he odo is i ele an o he ask.
Keywo ds Beha io al synch ony, Ol ac i e s imuli, In-phase synch ony, An i-phase synch ony, Coope a ion,
Compe i ion
In e pe sonal synch ony is a p e alen phenomenon ha is p esen in a ious ypes o human in e ac ions
and social con ex s. Fo example, i can na u ally a ise du ing conce s, whe e hy hm and ene gy c ea e a
unique collec i e expe ience1. In childhood, spon aneous synch oniza ion p ocesses a e hough o be linked
o a achmen and a eeling o connec ion wi h o he s. The abili y o child en o synch onize hei gaze,
mo emen s, and speech eme ges wi hin he i s ew yea s o li e2. De ined by DaSil a & Wood as he alignmen
o beha io and/o physiology du ing in e ac ions3, in e ac ional synch ony may occu a a ious le els o
human in e ac ion. Thus, synch ony may eme ge as he empo ally coo dina ed dynamics o ei he mo emen ,
ocal pa ame e s, physiological ma ke s, o o he non e bal indica o s in in e ac ing indi iduals.
The neu oscien i ic li e a u e has epo ed in e -b ain synch ony4, which co esponds o he synch oniza ion
o e ime o wo pa ne s’ cen al ne ous sys ems. Physiological synch ony has been s udied based on pe iphe al
measu es such as hea a e and elec ode mal ac i i y5,6. Finally, changes in an indi idual’s body pos u e o en
led o co esponding changes in he o he pe son’s body pos u e, whe he he wo we e iends, s ange s, o
spouses7, making mo emen synch ony an impo an aspec o s udy du ing social in e ac ion. Mo emen
synch ony, a speci ic ype o in e pe sonal synch ony, is e lec ed by he empo al aligning o a gi en mo o ac ion
among wo o mo e in e ac ing indi iduals8—people o en mi o each o he ’s mo emen s in a ime-co ela ed
way. This phenomenon can be obse ed in e e yday-li e si ua ions, such as when nodding in ag eemen , shaking
one’s leg, o shi ing pos u e when si ing du ing ace- o- ace discussions. Fo example, i du ing a walk, one
pa ne begins o inc ease walking speed, he o he is likely o inc ease walking pace o main ain synch ony
wi hin a ew seconds, wi hou e en ealizing bu wi h he in en ion o acili a e communica ion.
The no ion o mo emen synch ony was ea ly in oduced by Condon and Ogs on9. In hei s udy, manual
coding was applied o egis e changes in mo emen and pos u e occu ing be ween ames o ilm eco dings.
A a ious ange o pape -based me hods elied on judges who p o ided independen e alua ions based on ideo
eco dings10,11. Wi h he e olu ion o ideo echnology, mo emen synch ony has since been ex ensi ely s udied
1CNRS, UMR 9193 - SCALab - Sciences Cogni i es e Sciences A ec i es, Uni . Lille, 59000 Lille, F ance. 2Ins i u
Uni e si ai e de F ance (IUF), Pa is, F ance. 3Uni e si y Hospi al o Psychia y and Psycho he apy, Uni e si y o
Be n, Be n, Swi ze land. 4Psychology Resea ch Cen e (CIPsi), School o Psychology, Uni e si y o Minho, B aga,
Po ugal. 5SCALab UMR CNRS 9193, Uni e si y o Lille, Rue du Ba eau, BP20 60149, 59653 Villeneu e d’Ascq
Cedex, F ance. email: [email p o ec ed]
OPEN
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bo h in dyads and in la ge g oups using ideo eco dings and ame agging12–15. Howe e , hese app oaches
a e bound o obse a ional e o s and do no always p o ide he means o de ec he sligh changes in mo emen
synch ony, namely he in ensi y and di ec ion o co ela ional changes.
O e he las en yea s, a new me hod o quan i y beha io al synch ony using mo ion ene gy analysis (MEA)
has eme ged. MEA is an objec i e me hod ha p o ides he means o de e mine changes in he quan i y o
mo emen wi hin a gi en ime se ies. This app oach is an e icien al e na i e o manual a ings by an obse e —
which akes ime and is p one o e o s16. Using he MEA so wa e, i is possible o upload ideos and de ine
egions o in e es (ROI) and he so wa e au oma ically calcula es he quan i y o changing pixels de ec ed
wi hin he p e-de ined ROIs as a measu e o mo ion. MEA p o ides he mo ion ime se ies o bo h in e ac ing
pa ne s, which can hen be used o compu e mo emen quan i y and synch ony be ween he wo pa icipan s.
Mo emen synch ony in dyads is c ucial in a ange o si ua ions h oughou social li e. Fi s ly, synch ony
be ween wo people is associa ed o coope a ion du ing a wide numbe o asks. Dyads composed o same-
sex s ange s e ealed mo e absolu e mo emen synch ony when alking abou hings hey bo h disliked in
a un con ex a he han ha ing a deba e wi h wo opposi e posi ions16. O he s udies ha e epo ed ha
synch onized ac ions lead o mo e coope a ion han non-synch onized ac i i ies14. In an expe imen al s udy
in which pa icipan s walked a ound he campus oge he , synch onized oo s eps la e p edic ed dona ions
in a game in ol ing us and equi ing indi idual sac i ice o g oup bene i s17. Hence, i is hough ha ime
pe iods du ing which mo emen synch ony akes place may suppo he expe ience o sha ing a common goal18.
Synch ony be ween people impac s liking, us , and o he a ilia i e beha io s. In collec i e ga he ings,
highe pe cei ed emo ional synch ony was associa ed wi h s onge social suppo , and highe endo semen o
social belie s and alues, ein o cing he iden i y usion o he g oup19. The li e a u e also e ealed an in luence
o synch ony on pe cei ed simila i y and connec edness14. Mo e speci ically, a me a-analysis o 42 s udies on
beha io al synch ony epo ed ha , when compa ed o non-synch onous condi ions, synch ony inc eased
p osocial beha io s, social cogni ion, pe cei ed social bonding, and posi i e a ec i e s a es7. Mo emen
synch ony has also been sugges ed o play a ole in ma e choice, wi h e idence indica ing i s in luence on
a ac ion and ela ionship o ma ion20,21. The e ec o mo emen synch ony on social in e ac ion was ound
o eme ge e en when indi iduals a e unawa e o he spon aneous synch oniza ion phenomenon16. A possible
explana ion o his e ec migh be ha synch ony acili a es inciden al memo y o speech and appea ance o
he second pa ne 22. A iche memo y ep esen a ion o he pe son and in e ac ional expe ience would inc ease
he emo ional expe ience and associa ed empa hy. A second hypo hesis is ha in e pe sonal synch ony and
posi i e a ec i e s a es c ea e a be e en i onmen o in e ac ions. As o causal di ec ion, indings suppo ed
he in e p e a ion ha synch ony acili a es he eme gence o posi i e a ec i e s a es16.
Taken oge he , he abo e-men ioned s udies suppo he key ole o mo emen synch ony o posi i e
social cohesion. These indings open he doo o nume ous pe spec i es in heal h and social psychology. A key
ques ion is now whe he i is possible o modula e—and especially imp o e—social in e ac ion by changing he
deg ee o synch ony be ween indi iduals du ing a social ask. Fo his, we mus a i e a a be e unde s anding
o he en i onmen al ac o s ha in luence he le el o synch ony be ween indi iduals. This ques ion has
su p isingly igge ed e y ew s udies. The scien i ic li e a u e desc ibes he ela ion be ween synch ony and
o he ac o s such as coope a ion and empa hy, bu o ou knowledge, no s udies ha e ied o use augmen ed
senso y en i onmen s o enhance mo emen synch ony be ween wo indi iduals.
An en i onmen al ac o ha could modula e he le el o mo emen synch ony is odo s. The sense o smell is
phylogene ically he oldes senso y sys em and has impo an implica ions o su i al ins inc s by in luencing
mo o execu ion h ough app oach and a oidance beha io s23. In addi ion o in luencing ou emo ions and
mo emen s, odo s can indeed in luence social beha io s. Resea ch examining he e ec o odo s on social
in e ac ion showed ha pleasan odo s we e associa ed wi h al uis ic beha io s. Mo e speci ically, Ba on
epo ed ha pa icipan s su ounded by a pleasan odo we e mo e likely o spon aneously help a s ange han
when no odo was di used24. Odo s can in luence p oblem-sol ing, as unpleasan odo s ha e been shown o
dec ease coope a ion be ween indi iduals25. The ew scien i ic s udies published in he ield o social psychology
ha e highligh ed he possibili y ha when asked o sol e a p oblem in a oom whe e a pleasan odo is di used,
a g oup ends o se highe goals, make mo e concessions, and is o e all mo e e icien 26. Gi en ha peppe min
odo is known o heigh en a ousal and a en ional ocus, i may no only inc ease o e all mo emen bu also
acili a e g ea e synch ony be ween in e ac ing pa ne s by ein o cing social e iciency, al uism and sha ed
engagemen in he ask27. The aim o he p esen s udy was o assess whe he he use o an ambien pleasan
peppe min odo could modula e mo emen synch ony du ing h ee ace- o- ace social asks.
We hypo hesized ha pe cei ed a ousal and posi i e alence will be highe in he odo condi ions han
in he no-odo condi ions (H1). In addi ion, he un ask will inc ease posi i e alence in compa ison o he
compe i ion and coope a ion asks (H2). The hi d hypo hesis s a es ha he pa icipan s will mo e mo e in
he odo condi ion han in he no-odo condi ion (H3). Di using a peppe min odo in he en i onmen will
also inc ease mo emen synch ony in all asks (i.e., coope a i e, un, and compe i i e asks; H4). Following he
indings o Tschache e al.16, a un a mosphe e enhances he deg ee o in e pe sonal synch oniza ion in dyads;
hus, we hypo hesized ha mo emen synch ony will be highe in dyads in he un ask han in he coope a ion
and compe i ion asks (H5).
Resul s
The esul s epo ed he ea e conce n he cha ac e iza ion o a ec i e s a es, quan i y o spon aneous mo emen
and he deg ee o mo emen synch ony in he coope a i e, un, and compe i i e asks p oduced in odo and no-
odo en i onmen s. O e all, he e we e no signi ican e ec s o o de . Hence, mean esul s a e epo ed.
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A ec i e s a es
The median sco es o he a ing o he pe cei ed a ec i e s a es ob ained om he a ec g id a e p esen ed in
Fig.1, o a ousal (bo om) and alence ( op).
Valence
The RM ANOVA showed a signi ican e ec o Task on pe cei ed alence, F(1,50) = 5.11, p = 0.028, η2p = 0.09,
wi h highe sco es o posi i e a ec i e alence in he un ask (n = 100, M = 7.270, SD = 1.462) han in he
coope a ion (n = 100, M = 6.760, SD = 1.154) and compe i ion asks (n = 100, M = 6.960, SD = 1.415). Pos hoc
analyses con i med ha pe cei ed alence in he un ask was signi ican ly highe han in he compe i ion ask
( = − 2.917, p = 0.011), while no signi ican di e ences we e obse ed be ween he coope a ion and un asks
( = − 1.74, p = 0.249) o he coope a ion and compe i ion asks ( = − 1.177, p = 0.720). The e ec o Odo and he
Odo × Task in e ac ion we e nonsigni ican (p = 0.457 and p = 0.807, espec i ely). O e all, he esul s indica ed
ha pa icipan s epo ed mo e pleasu e when engaging in he un ask han in he wo o he asks. Ambien
posi i e odo s did no signi ican ly change he pleasan ness o he expe ience.
A ousal
The RM ANOVA did no e eal a signi ican e ec o Task (p = 0.188), Odo (p = 0.527), o Odo × Task
in e ac ion (p = 0.347) on pe cei ed a ousal. O e all, hese esul s indica ed ha he e we e no changes in he
pe cei ed a ousal le els ac oss expe imen al condi ions.
Quan i y o body mo emen
The mean sum o mo emen is depic ed in Fig.2 as a unc ion o he ask. The RM ANOVA showed a signi ican
e ec o Task on he sum o mo emen s (F(2, 215534) = 2030.83, p < 0.001, η2 = 0.009), wi h mo e mo emen s
obse ed in he compe i ion ask (M = 366.423, SD = 373.089) han in he coope a ion (M = 302.832, SD = 368.406)
and he un asks (M = 321.853, SD = 386.900). Pos hoc es s e ealed ha mo emen s we e signi ican ly highe
in he compe i ion ask compa ed o bo h coope a ion ( = 63.781, p < 0.001) and un asks ( = 42.373, p < 0.001).
Addi ionally, he coope a ion ask esul ed in signi ican ly ewe mo emen s han he un ask ( = − 18.589,
p < 0.001).
The e ec o Odo and he Odo x Task in e ac ion we e nonsigni ican (p = 0.347 and p = 0.698, espec i ely).
O e all, he esul s indica ed ha pa icipan s mo ed mo e du ing he compe i ion ask han du ing he un
and coope a ion asks. Ambien odo did no in luence he quan i y o spon aneous body mo emen s ac oss
pa icipan s.
Deg ee and na u e o mo emen synch ony
Figu e3 (le ) p esen s an illus a ion o desc ip i e esul s o he mo emen ime se ies ob ained in wo
pa icipan s (P01 and P02) o a ypical dyad (D11). On he y axis, one can see he quan i y o mo emen eco ded
Fig. 1. Mean alence sco es ( op) and a ousal sco es (bo om) as a unc ion o ask (Compe i i e, Coope a i e,
Fun) when engaging in an ambien odo en i onmen ( igh ) o an ambien odo less en i onmen (le ).
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by mo ion ene gy analysis ac oss ime (s). The SUSY so wa e hen calcula es he c oss-co ela ions be ween
pa icipan s. Figu e3 ( igh ) p esen s he ue da a (p esen ed in g een) ha was ob ained o he ypical dyad 11.
To con ol o andom o coinciden al synch ony, SUSY also enables he calcula ion o shu led da a (p esen ed
in ed). The compa ison be ween he ue and he shu led da a indica es he le el o ue synch ony ha was
Fig. 3. LEFT PANEL: Visualiza ion o he quan i y o mo emen o e ime (in seconds) o wo indi iduals in
he same dyad pe o ming he ‘Fun’ ask. RIGHT PANEL: Resul s om he SUSY algo i hm applied o he aw
da a o compu e he mean synch ony alues (g een cu e) and o he shu led da a o compu e mean pseudo-
synch ony alues ( ed cu e) as a unc ion o e en lag. The h ee boxes in he igh panel highligh pe iods o
di e en synch ony s a es: he ed box indica es an i-phase synch ony (co ela ion below pseudo- andomized
da a), he blue box indica es no synch ony (simila synch ony and pseudo-synch ony le els), and he g een
box indica es in-phase synch ony (co ela ion abo e pseudo- andomized da a).
Fig. 2. Mean sum o spon aneous body mo emen s as a unc ion o ask (Fun, Coope a i e, Compe i i e).
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used in he ollowing o ob ain he main s a is ical esul s. We also p esen in Fig.3 ( igh ) h ee windows o
illus a e he ypical pa e ns ha would be expec ed o an i-phase synch ony ( ed block), absence o synch ony
(blue block) and o in-phase synch ony (g een block).
The s a is ical esul s a e p esen ed he e a e . When con as ed o 0, he s uden - es showed a signi ican
le el o mo emen in-phase synch ony in he un ask ( = 5.547, p < 0.001) bu no in he compe i ion
( = − 1.174, p = 0.246) o in he coope a i e asks ( = − 0.887, p = 0.379). When examining he e ec o odo
p esence, mo emen synch ony le els did no di e om 0 in ei he he odo ( = 1.704, p = 0.093) o he no-odo
condi ions ( = 1.534, p = 0.129).
The mixed-e ec s model indica ed a signi ican e ec o Task on he le el and he sign o mo emen synch ony
(ES[no-abs]), F(2,25) = 19.84, p < 0.001, wi h mo e in-phase synch ony in he un ask (n = 25, M = 4.559,
SD = 6.672) han in he coope a ion ask (M = − 0.655, SD = 5.159). Resul s indica ed a endency owa ds an i-
phase synch ony o he compe i ion ask only (n = 25, M = − 1.550, SD = 5.409). Pos hoc analyses con i med
ha mo emen synch ony in he un ask was signi ican ly highe han in bo h he compe i ion ( = − 5.098,
p < 0.001) and he coope a ion asks ( = − 5.036, p < 0.001), while no signi ican di e ences we e ound be ween
he compe i ion and coope a ion asks ( = − 0.062, p = 0.998). The main e ec o Odo was nonsigni ican
(p = 0.274). Mean e ec s a e epo ed in Fig.4.
Discussion
We explo ed he p esence o mo emen synch ony in dyads o same-sex iends who came oge he o he
labo a o y and engaged in h ee games. The asks we e pe o med in a oom wi h o wi hou ambien peppe min
odo . The main objec i e o his esea ch was o assess whe he mo emen synch ony would be g ea e du ing
a p o-social ask and whe he his phenomenon would be u he enhanced by he p esence o pleasan odo s.
O e all, he esul s on he ask e ec indica ed ha pa icipan s mo ed mo e in compe i ion bu synch onized
mo e in he un ask. The un ask was ound o be associa ed wi h mo e posi i e a ec i e s a es, con i ming H2.
These esul s eplica e in a sample o dyads o iends he same ask e ec as epo ed by Tschache e al.16 o
which dyads o s ange s we e ec ui ed. Ne e heless, in hei s udy, mo emen synch ony was analyzed only
on absolu e alues. As a esul , i was no known o da e whe he synch ony was due o in-phase o an i-phase
synch oniza ion phenomena.
When wo indi iduals become coo dina ed, wo con as ing modes o synch ony can eme ge28: in-phase
synch ony (i.e., co a ia ions o he indica o s occu ing in he same di ec ion) and an i-phase synch ony (i.e.,
co a ia ions o he indica o s occu ing in he opposi e di ec ion). Many s udies in he ield o social in e ac ion
ha e ocused on synch ony wi hou di e en ia ing in-phase om an i-phase synch ony. Howe e , in-phase and
an i-phase in e als may se e di e en unc ions and play con as ing oles in he embodied expe ience o
social in e ac ion6. Hence, o gain a ue pic u e o he in e ac ional phenomenon, i is necessa y o adop a ool
ha p o ides he means o dissocia e an i-phase and in-phase synch ony. In he p esen s udy, we employed
he Su oga e Synch ony (SUSY) s a is ical so wa e, which allows o he di e en ia ion be ween hese wo
ypes o synch ony. Resul s indica ed a endency owa ds an i-phase synch ony in he compe i ion ask (i.e.,
he mo emen o pa icipan A and B co- a ied in he opposi e di ec ion indica ing ha , when pa icipan A
mo ed mo e, pa icipan B mo ed less). In he un social se ing, ou dyads p esen ed highe le els o in-phase
in e pe sonal synch ony (i.e., he mo emen o pa icipan A and B co- a ied in he same di ec ion). These
indings con i med H5; hey s ess he impo ance o looking a di ec ion o co- a ia ions by epo ing a key
ole played by in-phase synch ony o p o-social beha io s. Speci ically, in p e ious wo k, in-phase mo emen
synch ony was epo ed o be igge ed by asking pa icipan s o synch onize in en ionally hei mo emen s
o he mo emen s o ano he 14,17. The esul s o hese s udies demons a ed a bene icial e ec o in-phase
synch oniza ion on coope a ion, social a achmen , cohesion, posi i e a ec , and a ilia i e beha io s. Fo u u e
wo k, i would be o in e es o s udy in g ea e dep h he unc ional ela ion be ween a ec i e s a es and in-
phase synch ony o cla i y hei causal ela ionship and in luence on p o-social a i udes.
To measu e and compu e he le el o spon aneous mo emen synch ony, mo ion ene gy analysis (MEA)
was used in he p esen s udy. As a quan i ica ion ool o mo emen quan i y and mo o synch ony, MEA has
he ad an age o being objec i e and hus, ee o a a e ’s in e p e a ion o he meanings o non e bal ges u es
and pos u e shi s. MEA also p o ides he means o dissocia e be ween in-phase and an i-phase synch ony in a
na u al se ing wi hou in e e ing in he ace- o- ace in e ac ion. In he p esen s udy, we de ined he body o
each indi idual as he c i ical egion o in e es (ROI). I is he case ha MEA o e s also he means o delimi a e
sub-ROIs (e.g., head, oo , uppe body, e c.). Fo example, Ramseye and Tschache epo ed ha du ing
he apy-pa ien in e ac ions, head synch ony be e p edic ed he apy ou come han lowe body synch ony, wi h
longe las ing e ec s wi h head synch ony speci ically29. Howe e , o use sub-ROIs he e is a necessi y o se a
s ong cons ain on indi iduals’ eedom o mo e. To ensu e sound da a, he sub-ROIs mus emain s a iona y
om one ame o he nex wi hin he ideo sequences. In he s a iona y MEA e sion, he sub-ROI ames do
no adap dynamically o body shi s. Hence, in he p esen s udy, we could no in es iga e whe he sub-ROI
synch ony ook place. In u u e s udies, a dynamic MEA e sion could be de eloped by aking ad an age o he
au oma ic isual acking algo i hms ha a e oday being implemen ed in mo ion-cap u e echnologies30. Then,
i would be o in e es o con i m he in-phase e ec s o he un ask on uppe -body speci ically, wi hou he
need o cons ain pa icipan s om using non e bal ges u es du ing social engagemen . Such a ool would open
new pe spec i es o he modeling o dynamics o in-phase synch ony ac oss body segmen s in na u al se ings.
E ec s o ambien odo s
The e was an absence o e ec o he peppe min odo . Hence, H1, H3 and H4 we e no con i med. Ne e heless,
we ook ca e o e i y ha he ambien peppe min smell was abo e h eshold and was consciously pe cei ed
by he majo i y o he pa icipan s. A o al o 65% o he pa icipan s e en ecognized he smell as min . Hence,
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i seems ha in a social ask ha equi es cogni i e engagemen , he odo en i onmen had li le impac on he
pleasan ness o he expe ience. Fu he mo e, he odo en i onmen impac ed nei he he quan i y o exp essed
mo emen no he deg ee o mo o synch ony.
The absence o an odo e ec may be ela ed i s o he choice o he odo i sel . Peppe min is a s imula ing
odo ha inc eases ale ness and oxygen in ake by opening he lung cage27. Peppe min -odo en i onmen s
ha e been epo ed in clinical se ings o allow pa icipan s o educe hei sensa ion o a igue and imp o e
Fig. 4. Mean deg ees o synch ony as a unc ion o ask (Top panel) and ambien odo en i onmen (Bo om
panel).
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mood31,32. Peppe min anks highly in sel - a ed scales, being epo ed as e y pleasan , in ense, and highly
s imula ing33. Peppe min odo is also known o enhance physical pe o mance in a hle es, such as i s di ision
B azilian socce playe s34. Howe e , in ou s udy, he ask was cogni i e. Hence, peppe min -odo may ha e an
impac in si ua ions o which he physiological sys em needs o espond, bu i may no be ins umen al o he
cogni i e load o social in e ac ion.
Mechanisms o a en ion se e o acili a e he selec ion o app op ia e e en s om noisy en i onmen s
encoun e ed du ing e e yday ac i i ies. Indeed, he e is a common and limi ed pool o a en ional esou ces o
he p ocessing o senso y in o ma ion such as isual, audio and ol ac i e s imuli35. Humans di ec an a en ional
spo ligh wi hin spa ial coo dina es ha a e nea hem, in bo h ision and audi ion. Some s udies sugges ha
odo s do no cap u e a en ion unde he same p inciples36,37. In social asks ha do no in ol e ol ac o y
s imuli, he need o ol ac o y selec i e a en ion is limi ed, and he e o e, he spa ial ocus on ol ac o y s imuli
is less ele an 38. Fo example, in a s udy p esen ing neu al pic u es, pa icipan s we e asked o epo which
senso y changes occu ed in he en i onmen . While many pa icipan s epo ed a manipula ion in luminance
which did no occu , only h ee ou o 93 no iced he manipula ion o smell39. Humans a e cha ac e ized by a
e y s ong isual specializa ion, as is he case o mos p ima es, making isual s imuli mo e likely o cap u e
a en ion in social asks han odo an s imuli40. Ne e heless, a ew s udies ha e epo ed he powe o nega i e
odo s o igge beha io changes41,42. I would be o in e es in u u e s udies o es whe he unpleasan odo s
would ha e a s onge powe o cap u e a en ion han pleasan peppe min .
Ano he possible explana ion o he absence o an odo e ec in he p esen s udy is ha peppe min is
no an odo ha is encoun e ed na u ally, especially, in a labo a o y oom. Thus, he unexpec ed na u e o
he odo in ou speci ic con ex may ha e u ned he ambien peppe min odo in o a non ele an s imulus.
Mos pa icipan s would hen ha e unconsciously conside ed he odo as some hing o be igno ed. I may be
ele an o conside in u u e expe imen al designs he na u e o he ambien odo as a unc ion o ask and
con ex . Masculine body odo s ha e been epo ed o ha e a powe ul e ec on emale a ousal in ensi y43.
Hence, body odo s o example could be chosen speci ically o modula e mo o synch oniza ion as he odo
could play a magne ic ole in he deg ee and na u e o social ela ionships (swea , s ess and ashion pe ume
a e no cha ac e ized by simila odo molecules44). In ou iew, a be e unde s anding o ol ac o y cap u e o
a en ion o beha io modula ions equi es ha u u e wo k conside he odo con ex as p ima y and c ea e
mo e ecological si ua ions. In his sense, he smell o ca eine could be conside ed in he u u e, as ca eine odo
ends o enhance cogni i e ac i i y45. As such, pa icipan s could be in i ed o pe o m he social asks desc ibed
he e in a co ee shop, i.e., a place o which he odo o ca eine is expec ed. The ambien odo would he e be
cohe en wi h a high cong uency be ween he wo kspace and he ask; Ca eine could hen unc ion as a ue
boos e o mo o synch oniza ion h ough au oma ic cap u e o ol ac o y a en ion.
Implica ions and conclusion
The s udy o in e pe sonal synch ony has impo an social and clinical implica ions. Humans a e indi iduals
ha a e bo n and g ow o be social; bo h physical and men al wellbeing a e c ucially needed o insu e good
social unc ioning. Unde s anding social p ocesses, such as in e pe sonal synch ony, is essen ial o be e
comp ehend adap i e social ela ionships. In many common si ua ions (e.g., s ess ul wo kplaces), social
synch ony is impai ed46. The same is e iden in di e en pa hologies, such as in au ism spec um diso de s47,48,
ma e nal dep ession49, schizoph enia o social anxie y diso de 50. Gi en he implica ions o synch ony in human
in e ac ions, he comp ehension o how augmen ed senso y en i onmen s can modula e o e en enhance he
deg ee o in e pe sonal synch ony in dyads is c ucial o imp o e social in eg a ion in he gene al popula ion, and
in clinical popula ions in pa icula . The s udy o in e pe sonal synch ony has also implica ions o he clinical
aining o psychologis s, psychia is s and o he heal h p o essionals. Non e bal beha io s a e conside ed as a
p edic o o clinical e ec i eness and pa ien ou comes51. Thus, a deepe knowledge o he in e play be ween in-
phase synch ony and he en i onmen al ac o s is a scien i ic a enue o be encou aged.
The indings epo ed he e con i m ha mo emen synch ony is enhanced when pa icipan s eely engage
in a un cogni i e ask ha emphasizes he needs/abili ies o lis ening, speaking and dialog engagemen . Ou
indings showed ha in-phase synch ony cha ac e izes he posi i e phenomenon o social in e ac ion, which
was he case he e in he un condi ion. Compe i ion, on he o he hand, was agged wi h g ea e quan i ies o
mo emen and absence o mo emen synch ony be ween he wo pa icipan s. The limi ed e ec s o odo s on
mo emen synch ony should encou age u u e esea ch in he ield o ol ac o y neu osciences o gain in ime a
be e unde s anding o how odo s in luence he dynamics o human spon aneous synch oniza ion. Ne e heless,
we desc ibe he e a se ies o ecological social asks, wi h sound expe imen al me hods, and adequa e s a is ical
powe . This p ocedu e has he po en ial o guide u u e s udies on how o selec ambien odo en i onmen s o
modula e in e pe sonal synch ony.
Me hod
Pa icipan s
Heal hy adul s we e ec ui ed o he p esen s udy om he s a and s uden co pus o he uni e si y o
Lille (F ance). Rec ui men also included pa icipan s om he esea che s’ ne wo ks and olun ee s who
esponded o he s udy’s ad e isemen sha ed on a ious social ne wo ks. Each pa icipan was asked o come
o he labo a o y wi h a iend o he same gende . The wo pa icipan s we e e e ed o as a dyad. In o de
o pa icipa e in he s udy, pa icipan s had o be ee o any mo o dys unc ion o neu ological, audi o y, and
ol ac o y diso de s. Conce ning COVID-19 es ic ions, a le e o in o ma ion ega ding COVID-19 was
comple ed by each pa icipan .
The sample size equi ed o his s udy was calcula ed using G*Powe (3.1.9.2). The heo e ical sample size
was compu ed o a epea ed-measu ed analysis o a iance (RM ANOVA), wi h he esul s o Tschache e al.16
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o he ask e ec and Ma chlewska e al.25 o he odo e ec as g oup pa ame e s. The powe analysis indica ed
ha a minimum o 18 dyads we e equi ed o he ask e ec ( = 0.56; α = 0.05; 1-β = 0.85) and a minimum
o 22 dyads o he odo e ec ( = 0.314; α = 0.05; 1-β = 0.85). We con o med o he la ge numbe be ween
bo h e ec s, esul ing in a 22-dyads equi ed sample size. Th ee addi ional dyads we e collec ed o accoun o
e en ual ou lie s and echnical issues. In o al, 25 same-sex dyads ca ied ou he expe imen , wi h a majo i y o
emale dyads in he sample (n = 20).
The s udy was conduc ed in acco dance wi h he Decla a ion o Helsinki. All pa icipan s ecei ed an
in o ma ion le e and ga e w i en in o med consen p io o hei inclusion in he single expe imen al session.
In addi ion, all pa icipan s illed ou a pe mission o m o be ideo- eco ded and in o med consen was ob ained
o publish blu ed images in an online open access publica ion. The s udy was app o ed by he e hics commi ee
o he Uni e si y o Lille ( e e ence 2017-233-S52, NIRS Sensa ions 20/01/2022 addendum).
P ocedu e
Expe imen
Upon a i al a he labo a o y, he session s uc u e was explained o he pa icipan s and he expe imen e
made su e ha bo h indi iduals clea ly unde s ood he ask a hand by asking poin - o-poin ques ions.
Each dyad pa icipa ed in h ee di e en asks: coope a ion, compe i ion, and un discussion. The asks we e
p esen ed in a semi- andomized o de . Wi hin each ask si ua ion, he dyad pe o med unde wo condi ions:
odo and no-odo ials. Hence, a o al o six expe imen al condi ions we e pe o med by each dyad (see Fig.5).
Each condi ion included a 2-min baseline ollowed by he 5-min con e sa ion ask. These ime in e als we e
applied sys ema ically in all six condi ions (Task(3) * Odo (2)). In he odo condi ions, di usion o he ol ac i e
s imuli began a he s a o he ask, immedia ely a e he baseline. Hence, he e was always a leas a 2-min
ime in e al o se a clean and s able odo an en i onmen . Hal o he dyads pe o med he odo condi ion
be o e he no-odo condi ion. The o he hal o he dyads s a ed each ask by he no-odo condi ion and hen,
pe o med he odo condi ion. We applied his o de manipula ion o con ol o possible lea ning e ec s, as he
pa icipan s needed o epea each ask wice. In he p esen s udy, we used peppe min odo , and he pe ume
was di used a abo e h eshold o all indi iduals using ol ac o y speake s (Ol ahome E140, Odo aVision).
Task
The coope a ion ask was aimed o de elop coope a ion wi hin he dyads. Pa icipan s andomly d ew a social o
poli ical opic o common in e es om an u n (wi hou eplacemen ). Eigh di e en opics we e p epa ed, e.g.,
" o o agains compulso y mili a y se ice?"; "Fo o agains pocke money o child en?". These opics p o ided
he basis o a e bal deba e. Each pa icipan was p o ided wi h one o wo opposing w i en lis s o speci ic
a gumen s i ing hese opics, which hey could ead in a 2-min p epa a ion pe iod p io o he s a o he ial.
The coope a ion ins uc ion was o de elop a sha ed posi ion wi h he s onges a gumen s om he lis s.
In he compe i ion ask, he p ocess was simila , wi h a lis o a gumen s o and agains a speci ic opic
handed ou o he pa icipan s. The compe i ion ins uc ion was o a gue as con incingly as possible agains
he posi ion o hei pa ne . Unlike in he coope a ion condi ion, pa icipan s we e ins uc ed no o each a
comp omise. The compe i i e se ing was also p essu ed by he expe imen e , who ins uc ed each pa icipan
o win he deba e. Fo example, he expe imen e said "May he bes win" be o e he beginning o each ial.
The aim o he un ask was o c ea e a com o able, pleasan a mosphe e simila o ha expe ienced in a
humo ous, joy ul si ua ion among iends. Pa icipan s ecei ed ins uc ions o design a i e-cou se meal, o a
Fig. 5. Diag amma ic ep esen a ion o he expe imen al design o he h ee in e ac ion asks p omo ing
ei he a compe i i e, coope a i e, o un social a mosphe e.
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music playlis composed o i e songs. The ins uc ion was o he dyad o decide on dishes o songs ha bo h
iends de ini ely disliked.
Ma e ials
Ques ionnai es
A e each expe imen al condi ion, pa icipan s we e asked o indica e hei alence and a ousal le els on he
a ec g id52. In his g id, alence and a ousal a e a ed on a scale om 1 o 9. Fo alence, a sco e o 1 ep esen s
s ong nega i e a ec , 5 a neu al s a e and 9 s ong posi i e a ec . Fo a ousal, 1 ep esen s a low le el o
a ousal, 5 a neu al s a e and 9 a high le el o a ousal. Examples we e gi en o he pa icipan s so ha hey could
be e unde s and wha was mean by a ousal and alence. These sco es we e used o assess whe he he odo
en i onmen and/o asks had a speci ic e ec on he way each pa icipan expe ienced he session (H1 and H2).
Equipmen
The expe imen al sessions we e ilmed using a po able came a (GoP o HERO4 05.00, GoP o USA) a a
sampling a e o 30 Hz. The echnical p e equisi es o he ideo eco dings used by MEA so wa e53 a e a s a ic
came a posi ion and s able ligh condi ions wi h cons an shu e -speed and ape u e. To ensu e ha egions o
in e es (ROIs) would no o e lap, and people would no occlude one ano he on he ideo, pa icipan s we e
sepa a ed by a able o 1.5 m. Any objec likely o mo e was emo ed om he came a ield. In addi ion, whi e
sc eens we e added behind he pa icipan s in o de o inc ease he con as be ween indi iduals and he da k
oom walls. This con as enhancemen allowed o be e isualize he dyad mo emen s wi hin he ideo clips.
Two ROIs we e de ined in each ideo: he i s one o whole body o pa icipan 1 and he second one o whole
body o pa icipan 2 (see Fig.2, Panel A.1.). The ou pu o MEA so wa e a e he mo ion ime se ies o he ROIs
(see Fig.6).
Fig. 6. Illus a ion o a unique ypical dyad o he ou pu om he Mo ion Ene gy Analysis (MEA). The op
panel (le ) shows a clip om he ideo eco ding, while he igh panel displays he co esponding image om
he MEA so wa e wi h he wo de ined egions o in e es (ROIs). The bo om panel illus a es a ypical ime
se ies o indi idual mo ion ene gies, o he wo pa icipan s, as a unc ion o he p esence o odo (le ) and
ask condi ion ( igh ).
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