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a0005 SmilingD Messinger, University of Miami, Coral Gables, FL, USA

ã 2008 Elsevier Inc. All rights reserved.

Glossary

g0005 Anticipatory smile – A pattern in which a young

child smiles at an object and then gazes at another

person while continuing to smile, sharing positive

emotion about the object.

g0010 Duchenne smile – Smile involving eye constriction

(caused by orbicularis oculi, the Duchenne marker)

involved in the communication of intensely positive

emotion. Cheek-raise smile.

g0015 Joy – An emotional process characterized by

pleasurable feelings of engagement, a desire for the

engagement to continue, and action tendencies,

such as smiling, that tend to continue the

engagement.

g0020 Open-mouth smile – A smile involving a dropped

jaw typically occurring during arousing play.

Play smile.

g0025 Secure attachment – A categorization of infants and

toddlers who are able to explore the environment,

confident in their caregivers’ emotional and physical

availability should the need arise.

g0030 Simple smile – A typically weak smile that involves

neither the Duchenne marker nor mouth opening.

g0035 Smile – The sideways raising of the lip corners

caused by contraction of the zygomatic major.

g0040 Strong smile – Smile involving stronger contraction

of the zygomatic major.

s0005 Introduction

p0005 Early smiles are a prototypical expression of joy and awindow on the development of positive emotion. Smileselicit positive emotion and engagement in others, a pro-cess that contributes to the development of joy and socialcompetence in the young child. Infants express differentintensities and qualities of positive emotion throughalterations in the temporal and facial dynamics of theirsmiling and through the incorporation of other expressiveactions such as laughter and jumping up and down.Through the first two years of life, infant smiles andlaughter become increasingly social and affectivelyintense, and increasingly used in referential communica-tions about objects; between 2 and 4 years, smiles reflectthe social structure of peer interactions. Difficulties

with smiling in early interactions reflect a variety of riskconditions, while emotionally positive and responsiveinteractions can index optimal developmental trajectories.

s0010Historical Interest in the Study of Smiling

p0010Early smiling is the quintessential physical expressionof positive emotional engagement. Infant smiles appearto be direct behavioral expressions of joyful feelings(see Figure 1). This apparent link between behavior andmeaning has motivated over a century of research on theemotional significance, causes, behavioral correlates, anddevelopmental consequences of early smiling. Seminalfigures in child development have concerned themselveswith the meaning and causes of infant smiles. Freudregarded infant smiling as a signal of sensory pleasure andcontentment, while Piaget considered the smile of masteryan index of pleasurable accomplishment. In his work on theexpression of emotion, Darwin observed his own infants todeterminewhether their first smiles were expressions of joy.

p0015This article begins with a review of contemporarytheoretical perspectives on the emotional significance ofsmiling. It continues with an overview of the neurophysi-ology of smiling and common methods for measuringsmiling in infants, toddlers, and preschoolers. The articlecontinues with a discussion of smiling as a joyful processinvolving arousal regulation, a discussion which includesdefinitions of different types of smiling. A central sectionconcerns the development of smiling from the neonatal tothe preschool period. The penultimate section considershow smiling reveals deficits and competencies in infantswith various disabilities. The final section documents thedevelopmental continuity of smiling and its links withemerging social competencies.

s0015Theoretical Perspectives on EarlySmiling

s0020Behaviorist Approaches

p0020Social learning and behaviorist approaches suggest thatthe caregiver’s contingent responsivity to the infant’sactions produces increases in smiling. Smiling can, infact, be reinforced. If an examiner contingently respondsto an infant’s smiling with standardized periods of smiling,talking, and tickling, the infant will initially smile at anincreased rate. Infants, however, soon habituate to these

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reinforcers and smiling then declines precipitously.Behaviorism is one of the only theoretical approaches todivorce smiling from emotion. Behaviorist approaches tounderstanding smiling have been largely abandoned infavor of approaches that focus on the dynamic relation-ship of smiling to the infant’s emotional engagement withthe changing environment.

s0025 Cognitive Differentiation Theory

p0025 Cognitive differentiation theory maintains that joy islocated in the meaning of the environment to the infantand young child. Infants’ active cognitive understandingof events, and maybe even early awareness of their ownpleasure, is thought to be necessary for the emergence ofjoy. Cognitive differentiation theory holds that joy andother emotions develop out of more diffuse states suchas pleasurable positive valence. Early smiling, such as thattriggered when recognition of a visual stimulus elicits arelaxation in tension, is held to index pleasure but not joy.Joy is thought to develop around 9months of age andinvolve pronounced drops in cognitively mediated arousaland to be accompanied by particularly intense infantsmiling and laughing.

s0030 Discrete Emotion Theory

p0030 In contrast to a cognitive differentiation perspective,discrete emotion theory proposes that infant joy isexpressed in the infant’s first waking smiles. Discreteemotion theory emphasizes the role of brain-based affect

programs such as joy in organizing the output of multipleexpressive systems in the infant. Smiles and other infantfacial expressions are thought to directly express emo-tions produced by these discrete affect programs. By thisaccount, smiles index an irreducible joyful feeling statethroughout infancy, early childhood, and, indeed, theentire lifespan. Like other approaches, discrete emotiontheory suggests that joy motivates infants to approach andinteract in an affiliative fashion with caregivers and othersocial partners.

s0035Functionalist Theory

p0035While discrete theories locate joy within the infant, func-tionalist and dynamic theories locate joy in the relationshipof the young child and his or her often social environment.Functionalist theoretical perspectives emphasize the adap-tive role of emotions such as joy in the creation and mainte-nance of relationships with the environment, especiallythe infant’s social partners. The infant’s smiles and theinfant’s comprehension of the smiles of others are seen aspart of the process of pursuing and attaining goals in thesocial world.

p0040The functionalist emphasis on pursuing goals in rela-tionships is not limited to human beings. Extensive etho-logical research, guided by a functionalist perspective, haspainstakingly documented the communicative functionsof smiles and similar expressions in young monkeys andchimpanzees. Attachment theory also borrows from func-tionalist theory to describe the function of smiles from anevolutionary perspective. From the ethological and func-tionalist perspective represented by attachment theory,early smiles are attachment behaviors that maintain theproximity of caregivers to the infant.

s0040Dynamic Systems Theory

p0045Dynamic systems theory conceptualizes smiles and otherexpressive configurations as constituents of infant emo-tional processes. The process of smiling is part of theinfant’s experience of joy as well as an element in theinfant’s emotional communication with others. Dynamicsystems theory focuses on the bottom-up interrelation-ship between smiles and other constituents of social inter-actions. The theoretical approach focuses on the temporaldynamics of smiles and positive emotional processes. Theidea is that the formation of smiles during social interac-tion can provide insights into the emergence of smilingdevelopmentally.

s0045Summary and Overview

p0050These diverse theoretical perspectives offer differentdefinitions of positive emotion and different argumentsfor the association between positive emotions and smiling.

f0005 Figure 1 This 6-month-old infant’s strong smile involves the

Duchenne marker (eye constriction) and mouth opening.

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Despite their differences, there are clear areas of overlapbetween different theoretical perspectives. Cognitivedifferentiation theory’s emphasis on engagement in theemergence of smiling, for example, exemplifies thedynamic systems emphasis on the bottom-up emergenceof emotional expressions out of multiple interfacing con-stituents. Each perspective provides overlapping insightsthat will illuminate the presentation of the meaning anddevelopment of smiling in this article. Below, we reviewthe anatomical and neurophysiological basis of early smil-ing, and methods used to measure smiling.

s0050 The Neurophysiology of Smiling

s0055 Definition of Smiling

p0055 Physiologically, the contraction of the zygomatic majormuscle creates a smile by pulling the corners of the lipsupward and laterally (see Figure 1). The zygomatic isinnervated by the seventh cranial nerve, the facial nerve.The facial nerve emanates from the facial nucleus, agroup of motor neurons located at the level of the ponsin the brainstem.

s0060 Neurophysiology of Smiling

p0060 The facial nucleus receives inputs from two pathways.One pathway controls deliberate smiling and the othercontrols spontaneous expressive smiling. More deliberatefacial actions may occur when a young child is asked tosmile and involve pathways from the cortical motor stripthrough the pyramidal system. Spontaneous smiling pre-dominates in infancy and early childhood. Spontaneousfacial expressions involve an ‘extrapyramidal’ pathwaythat involves subcortical structures such as the basal gang-lia and amygdala.

p0065 Although spontaneous smiling is linked to joyful emo-tions, contemporary neuroimaging studies have notunambiguously identified structures that are activatedby positive emotions. Candidate structures include por-tions of the anterior cingulate cortex as well as subcorticalstructures mentioned above such as the basal ganglia. Thedegree to which neurophysiological studies identifylocalized structures involved in positive emotion is ofcentral importance to discrete emotion theory. Thistheory’s hypothesized modular affect program for joyrests on the eventual identification of specific structuresand pathways.

p0070 Robust evidence has been found for the association ofjoy with laterality differences in cerebral activation. Emo-tions involving an orientation or motivation to approach,particularly joy, are associated with greater left fron-tal cerebral activation than right. Laterality differencessuggest a distributed cerebral basis for positive emo-tional processes and processing, one involving multiple

networks of activation. This possibility is congruent witha wide range of theoretical perspectives such as cognitivedifferentiation and dynamic systems approaches.

s0065Measurement of Smiling

p0075Researchers typically measure the frequency and durationof infant smiling from videotaped records. Smiles andother emotional expressions are coded either with well-validated infant-specific coding systems, or according tostudy-specific criteria. These coding systems are also usedto measure a set of smile-related actions such as eyeconstriction (the Duchenne marker) and other communi-cative actions such as changes in infant gaze direction.Researchers may also code vocal, gestural, and whole-body expressions of infant emotion, such as jumping upand down in joy, as well as the facial and other expressiveactions of the caregivers and testers with whom the infantmay be interacting.

p0080Neonatal smiling is typically observed in hospitalnurseries, laboratories, and homes where early infant smil-ing in response to experimentally controlled visual andvocal stimuli such as the static image of a human face andhigh-pitched tones has been carefully documented. Socialsmiling between 2 and 6months of age is often studiedduring playful face-to-face interactions with a parent (seeFigure 2). These interactions are typically videotaped ineither the home or in a laboratory playroom and are usuallybetween 2 and 5 min in length. Individual infants typicallyshow a range of relatively stable levels of smiling in theseface-to-face interactions. Level of smiling during theseinteractions is also associated with more general ratings ofinfant emotional valence over 2–3 h home observations.

p0085Smiling is also measured during experimental proce-dures involving a period of parental nonresponsivity. Theface-to-face/still-face (FFSF), for example, is an experi-mental procedure in which a period of face-to-face play isfollowed by a period in which the parent is asked to hold astill-face and not respond to the infant; this is followed bya reunion episode in which the parent is asked to renewplay with the infant. Smiling typically declines precipi-tously in the still-face and rises in the reunion episode,though not quite to initial face-to-face levels.

p0090Through 48 months of age, smiling is often observedduring observations in the home, daycare settings, andpreschools, and observations in laboratory playrooms.Naturalistic observations may be supplemented or sup-planted with structured protocols carried out by a testeror parent such as tickling, peek-a-boo, and the presenta-tion of standardized stimuli such as a jack-in-the-box usedto document the development of positive emotion. Theseprotocols have been incorporated into structured assess-ments which, along with parental reports of positive emo-tion expression, are also used to assess individualdifferences in infant temperament.

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s0070 Smiling, Joyful Positive Emotion, andArousal

p0095 Smiles are simultaneously expressions of joy and indicesof arousal modulation. Early discrete emotion theories heldthat the basis of positive emotion is a sharp reduction inneurally based arousal. Cognitive theories held that positiveemotions involve active engagement with a challengingfeature of the environment followed first by recognitionand then by smiling. In support, infant heart rate – anindex of arousal – is more rapid during smiling than duringneutral expressions. Infants also accompany smiling with avariety of tension-reducing activities. Infants are likely toput their hands in their mouths while smiling and, after3months of age, tend to avert their gaze before endinga smile. Smiles may, in fact, be a mechanism for infantsto maintain visual contact with arousing features of theenvironment for as long as possible.

p0100 The general role of arousal in smiling is also relevantto links between smiles and negative emotional expres-sions. When a period of engagement yields an experiencethat the environment is safe and interesting, positive emo-tion and smiling results. When engagement yields anexperience of the environment as overwhelming andunsafe, negative affect results. This might occur, for exam-ple, when an interaction with a caregiver or parentbecomes temporarily overstimulating for the infant.

p0105 Although related to the management of arousal, thesmiles of infants and young children are also expressionsof joy. Smiles, for example, are perceived as more emo-tionally positive than neutral expressions, even amonginfants with serious facial deformities. The smiles ofinfants and young children are part and parcel of a processof positive engagement with the environment. They occurduring periods of interaction likely to elicit positiveemotion and tend to elicit positive emotion on the partof others. Smiles, then, can signal a desire for arousing

interaction even as they are part of a process or arousalmodulation. We now turn to a discussion of different typesof smiles and their role in the expression of positiveemotion.

s0075Different Types of Smiles

p0110The smiles of young children have different forms. Someappear to be tentative, others appear to communicate asense of personal connection, and yet other smiles appearto be part of hilarious outbursts. Infant smiles differ alonga variety of dimensions. They can be stronger and weakerand can involve different degrees of eye constriction (theDuchenne marker) and mouth opening. In this section,we explore evidence suggesting that different types ofsmiling express different degrees and types of positiveemotion.

s0080Simple smilesp0115Smiles that are not particularly strong, and do not involve

the Duchenne marker or mouth opening, are known assimple smiles. The types of situations in which infantsproduce simple smiles and ratings of those simple smilesindicate that even these smiles are more emotionallypositive than neutral expressions. A functionalist view offacial expressions in non-human primates offers addi-tional clues to the meaning of simple smiles. Chimpanzees(Pan troglodyte) possess a zygomatic major muscle active inproducing a bared teeth display that is similar to simplehuman smiling. The bared teeth display was originally asignal of submission (I accept your dominance). It hascome to be a signal of affiliation (I mean you no harm),which is frequently followed by behaviors such as holdingout a hand. Likewise, simple infant smiles may signify apositive affiliation with others that may be a steppingstone for more positive engagement. Infant simple smiles

f0010 Figure 2 Four-month-old infant and mother smiling interaction as captured by Automated Face Analysis at the Carnegie Mellon

University, Robotics Institute, compliments of Jeffrey Cohn, PhD. The infant and mother’s faces are outlined to illustrate lip movement,mouth opening, and eye constriction.

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occur, for example, during the warm-up phases of gamesand when infants are approached by an impassive stranger.

p0120 While simple infant smiles are emotionally positive,smiles involving stronger zygomatic contraction, eyeconstriction and/or mouth opening are more emotionallypositive than simple smiles. Below, we review evidencethat strong smiles, and smiles involving eye constrictionand mouth opening are more likely to occur during per-iods of interaction likely to elicit positive emotion thanare simple smiles and are perceived as more emotionallypositive than other smiles.

s0085 Smiles involving mouth opening (play smiles)

and smiles involving vocalizations

p0125 Infant smiles involving mouth opening caused by jawdropping have a specifically social and excited quality.They tend to occur while infants gaze at their mothers’faces and are typically perceived as reflecting morepositive emotion and arousal than closed-mouth smiles.

p0130 The open-mouth human smile is also morphologicallysimilar to the relaxed open-mouth display of nonhumanprimates. These displays develop in infant chimpanzeein the context of mock biting play with mothers. Likethe open-mouth smiles of human infants, these displayscommunicate playful, aroused engagement. Relaxedopen-mouth displays and infant open-mouth smiles arealso related to laughter. Laughter is a rhythmic, smile-linked vocalization that appears to index intense positiveemotion. More generally, infant vocalizations tend to beembedded within the time course of ongoing smiles suchthat the smiles are punctuated by the vocalizations. Thevocalizations may serve both to recruit attention to thesmile and to intensify the expression of joy.

s0090 Duchenne smiles

p0135 The Duchenne marker – eye constriction caused by orbi-cularis oculi, pars lateralis, which raises the cheeks towardthe eyes – is perhaps the best known index of smilingintensity in infants. Infants tend to produce Duchennesmiles when their mothers are smiling and when theyare approached by their smiling mothers. Infants alsoproduce more syllabic sounds when Duchenne smiling,a potential marker of emotional intensity. Duchenne smil-ing is also associated with greater relative activation of theleft than right frontal cerebral hemispheres, a patternwhich suggests greater approach orientation and joy.Although smiles involving the Duchenne marker areoften regarded as the only index of strong joyful emotionin adults, this distinction does not appear to be absolute ininfants. In infants, smiles with and without the Duchennemarker often follow one another directly in time, sugg-esting that infant Duchenne smiles are more intenseindices of positive emotion than smiles without theDuchenne marker.

s0095Strong smiles

p0140Smiles are continuous muscular processes in which thedegree of zygomatic contraction determines the strengthof the smile, the degree of lip corner movement. Strongsmiles index more intensely positive emotion, the infant’spositive emotional engagement with ongoing activities.More exciting parts of games elicit stronger smiling thanthe preparatory phase of the games. Tickling, for example,is accompanied by stronger smiling than getting ready totickle or pretending to tickle. Smiles involving strongerzygomatic contraction are also perceived as more positiveand joyful than weaker smiles.

p0145Stronger smiling – involving greater zygomatic con-traction – tends to be associated with eye constriction andmouth opening. Simple smiles without these features arethe weakest while smiles involving both eye constrictionand mouth opening are the strongest (see Figure 3).These intensity parameters vary together in time overthe course of an infant smile. As the strength of an infant’ssmiles increase and decrease, the degree of eye constric-tion and mouth opening involved in the smile, alsoincrease and decrease.

s0100Combined strong, open-mouth Duchenne smiles

p0150Infant smiles involving the Duchenne marker tend toinvolve mouth opening (and vice versa) (see Figure 1).These combined smiles – sometimes calledduplay smiles –tend to occur during unambiguously positive period ofinteraction such as when young infants are gazing at theirsmiling mothers. Strong smiles involving mouth openingand eye constrictions are perceived as the most joyful ofinfant smiles. They occur in circumstances – such as whilebeing tickled – which appear likely to elicit the strongestand most engaged positive emotion.

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f0015Figure 3 Mean smile strength of different smile types.

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s0105 Conclusion: The meaning of different types of

smiles

p0155 It is possible that Duchenne smiles are involved in reci-procating another’s positive emotion, while open-mouthsmiles involve a more aroused, playful quality of positiveemotion. If different types of smiles have qualitativelydifferent meanings, this would challenge the discreteemotion theory proposition that there is single affectprogram for joy. An alternate possibility – that differenttypes of smiles express different degrees of a singledimension of positive emotion or joy – is consonant witha wide range of theoretical perspectives. Discrete emotionand cognitive theories are congruent with this dimen-sional perspective, although the dimensional perspective’semphasis on real-time changes in smiling intensity havebeen a more central concern of functional and dynamicsystems approaches.

s0110 The Development of Smiling

s0115 Developmental Overview

p0160 The development of smiling reflects the emerging cogni-tive, social, and emotional competencies of the youngchild. Smiles first emerge during sleep during the neona-tal period and rapidly become a centerpiece of face-to-face social interactions in the first half year of postnatallife. Between 6 and 12months, infants begin to intention-ally communicate desires and experiences about objectsand events in the world to their communicative partners.Between 12 and 48months, smiling and laughter withinthe parent–child dyad becomes more sophisticated andintricate. At the same time, the smiles of young childrenbecome essential features of their social interactions withpeers. We review these developments below.

s0120 Neonatal and Early Smiling: 0–2 Months

s0125 Neonatal smiling: 0–1 month

p0165 Neonatal smiles are an emotional puzzle. They arereferred to as endogenous or spontaneous smiles becausethey are prompted by internal stimuli, suggesting theyhave no emotional content. Neonatal smiles occur morefrequently in sleeping and drowsy states of rapid eyemovement (REM) – about one smile every 5min – thanin other states. These smiles, however, do occur in otherbehavioral states, including states of alertness, suggestingthe possibility that they are related to positive emotion.

p0170 The form of neonatal smiles suggests an association withpositive emotion. Neonatal smiles can have a relativelymature form that involves strong muscular contractionsand the Duchenne marker. These smiles occur againsta backdrop of frequent lip and mouthing movements.Nevertheless, approximately one-third of these neonatal

smiles are recognized by untrained observers, suggestingtheir potential signal value.

p0175Neonatal smiling is unrelated to ‘gas’ as its frequency isunaffected by time since last feeding. Instead, neonatalsmiling appears to have a subcortical origin, as evidencedby the observation of neonatal smiling in an infant withmicrocephaly. Infants born prematurely show more neo-natal smiling than full-term newborns and the quantity oftheir endogenous smiling declines with age. These factorsalso suggest a subcortical origin for neonatal smiling,which may limit the emotional meaning of these smiles.

p0180Theoretical perspectives differ on the meaning ofneonatal smiles. While discrete emotion theory suggeststhat neonatal smiles – at least those occurring duringwaking states – are expressions of joy, a cognitive differ-entiation perspective regards them as physiologicalresponses to internal or environmental stimuli. Neonatalsmiles illustrate the dynamic systems emphasis on hetero-chronicity; that is, the neonatal smile appears to developphysically before it is integrated into patterns of cognitiveengagement and social interaction that provide evidencefor joyful emotion.

s0130Early smiling and the transition to social smiling:

1–2 months

p0185Over the first 2 months of life, smiling becomes graduallylinked to environmental stimulation, which sets the stagefor the emergence of social smiling. Infants first smile inresponse to auditory stimuli, and then respond to auditoryplus visual stimuli, and finally smile in response to visualstimuli alone. Specifically, through 1month of age, infantsmiles often occur during states of drowsiness or evensleep when they are elicited by high-pitched tones includ-ing the human voice. After 1month, smiles during alertstates are increasingly elicited by visual stimuli such asgazing at a face or an upright image of a face. Infantsbecome increasingly likely to smile to high-pitched audi-tory stimuli (such as the human voice) or visual displays(particularly static images of the human face) until about3 months of age.

p0190Cognitive differentiation theory maintains that whileneonatal smiles involve a reduction in physiologicalarousal, the smiling of young infants involves a reductionin psychological or cognitively modulated tension. It isthe emerging psychological meaningfulness of visual sti-muli rather than their physical/perceptual properties thatoccasions smiling. In support of this proposal, as infantsbecome more capable of rapidly recognizing more com-plex stimuli in the first months of life, latencies to smiledecrease. This cognitive differentiation perspective is alsorelevant to the emergence of social smiling, to which wenow turn.

p0195Social smiling develops in a developmental periodwhen infants are spending less time asleep and moretime in periods of alert inactivity, awake but not fussing

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or crying. These states facilitate social interaction asinfants spend increasing amounts of time gazing at thecaregiver’s face. The period in which social smiles emergeis also marked by the development of new patterns ofvisual attention between 1 and 2months of age. One-month-olds gaze alternately at the edge of the head andthe eyes. Two-month-olds gaze between the edge of thehead, the eyes, and the mouth. This more integrativepattern of gazing suggests attention to the facial expres-sion of others which may also facilitate social smiling.

p0200 Social smiles typically first occur while gazing at theparent in the 4–6weeks after birth. Age of social smilingappears to be contingent on a certain level of neurologicalmaturity. For infants born prematurely, age of social smil-ing must be adjusted to account for the number of weeksthe infant was born before due date. Maternal reports ofthe first social smile precede tester’s first elicitation ofsocial smiles by several weeks. Parents may experienceinfant’s first social smiles as providing a sense of connec-tion, fulfillment, and even reward (‘my baby recognizesme’) after the hard, sometimes sleep-depriving work ofcaring for a neonate.

p0205 In the first month of postnatal life, infants gaze at andaway from mother’s face without smiling. In the secondmonth, the social smile emerges, heralded by periods ofconcentration. Several seconds of brow knitting and visualfixation of the mother’s face are followed by relaxation ofthe brows, indexing apparent cognitive recognition, and asmile. This pattern links processes elucidated by cognitivedifferentiation perspectives to the emergence of socialsmiling. Dynamic systems approaches indicate – in com-plementary fashion – that the real-time occurrence of thisattention-related smiling pattern may provide a windowinto the first developmental emergence of smiling.

s0135 The Development of Social Smiling inFace-to-Face Interaction: 2–6 months

p0210 Social smiles develop during interaction. The periodbetween 2 and 6months is one of intense social interac-tion and rapid emotional development. During thisperiod, infants become both increasingly responsive tothe smiles of others and increasingly likely to initiatesmiles to others. We begin this section with a discussionof general features of smiling in face-to-face interactionand then turn to the development of interactive smilingbetween 2 and 6months.

s0140 General features of face-to-face interactive

smiling

s0145 Overview of infant and parental activities during

interactive smiling

p0215 Overall, infants smile for about one-fifth of face-to-faceinteractions and smiling typically occurs in bursts of smilesseparated by periods without smiling. Infant interactive

smiling is strongly linked to gazing at the parent’s face andsmiling tends to be associated with vocalizations that arealso used to express positive emotion.

p0220During face-to-face interactions, infant smiles are ahigh point of play with both mothers and fathers. Fatherstend to employ a more physical style of play with theirinfants (e.g., bouncing games) whereas mothers rely moreon visual and vocal expressivity to elicit smiles. Althoughthe term mother is often used in this article because of thepreponderance of research findings on mothers, mothersand fathers are equally adept at eliciting smiles fromtheir infants.

p0225During interaction, parents both stimulate and enter-tain their infants, attempting to elicit engagement andexpressions of positive emotion while at the same timeattempting to prevent and modulate their infants’ fussingand crying. In addition to smiling, parents hold, touch, andtickle their infants, move toward and away from the infant,and engage in high-pitched infant-directed speech. Theserhythmic multimodal displays increase and decrease inemotional intensity over the space of several seconds inconcert with and in reaction to infant smiles and otherexpressive actions.

s0150Infant and mother responsivity to smiling

p0230A key feature of interaction is the degree to which eachpartner influences and is responsive to the other.Mothers’ smiles and vocalizations are typically necessaryto elicit infants’ smiles but may not be sufficient to elicitinfant smiles. Mothers are optimally successful at elicit-ing infant smiles when they combine different communi-cative modalities with smiling such as vocalizing, leaningtoward the infant, and smiling simultaneously.

p0235Infant smiles are more likely to elicit mother smilesthan mother smiles are to elicit an infant smile. An infantsmile is typically sufficient to elicit a mother smile, usu-ally within a relatively brief two second time interval. Infact, an infant neutral gaze at mother’s face is often suffi-cient to elicit a mother smile, and mothers frequentlyinitiate smiles in the absence of discrete infant behaviors.Infants, then, may experience parental contingency in themidst of a wide array of parental expressive behaviors.

s0155Patterns of infant and mother smiling

p0240As suggested by a dynamic systems perspective, infant andparent individual propensities toward smiling combine tocreate more complex dyadic patterns of interaction intime. Infant smiles typically occur when the infant gazesat the mother and the mother smiles. Once infants aresmiling, parents will rarely cease smiling, which wouldbreak off a bout of mutual smiling. The young infant’sexperience of smiling, then, is, prototypically, smilingwith a smiling parent.

p0245Infant and mother also impact one another continu-ously in time. Stronger smiling on the part of the infant is

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likely to lead to stronger mother smiling. Stronger mothersmiling may be mirrored by the infant or the infant maydisengage, gazing away to regulate their levels of arousal.These levels of interactive influence vary among differentinfant–parent dyads. Generally, however, infant expres-sions of joy are mirrored and intensified by the parent.The infant responds to this intensification with eitherintensified engagement and positive emotional expressionor disengagement, gazing away, and terminating smiling.

p0250 The exchange of smiling is a nonverbal dialogue whosetopic is the shared experience of joy and the regulation ofemotion. Prototypically, infants’ experience of positiveemotion as they smile is mirrored back in intensifiedform by the smiling parent. The infant perceives thisincrease in the parent’s smile and simultaneously per-ceives his or her own increase in positive emotion thatthe parent’s smile engenders. Sources of the infant’s posi-tive responsiveness to the parent’s smile may be mirrorneurons or related neurophysiological processes that pro-duce feelings of sympathetic joy in the infant who per-ceives the smile of another.

p0255 Whatever the source, infants’ awareness of their ownchanging feelings occurs in concert with their experienceof their impact on the parent. The dynamic interplay thatresults suggests that one path to the development of joyinvolves experiencing the joy of another. The infant’ssimultaneous awareness of their own feelings and thoseof the parent is known as primary intersubjectivity. Wenow turn to the development of primary intersubjectivityand interactive smiling between 2 and 6months.

s0160 Developments in interactive smiling between

2 and 6 months

p0260 As infants develop and increase their smiling around2months, there is a related increase in positive maternalexpressions such as smiling. Infants appear to becomeaccustomed to specific levels of positive responsivitysuch that 2-month-olds smile less at a stranger who iseither more or less contingently responsive to the infantthan the infant’s mother. Early on, then, infants appear toshow dyad-specific levels of interactive contingency thataffect smiling levels. This may be one mechanism throughwhich infants between 2 and 6months increasingly differ-entiate between adults and come to reserve their smilingto a familiar attachment figure.

p0265 The development of smiling in face-to-face interactionoccurs concurrently with changing patterns of infantattention to the caregiver’s face. Between 2 and 6months,infants spend decreasing periods of time gazing at theirmothers’ faces but become increasingly likely to smilewhen they are gazing at the mother’s face. As infant smilesbecome more strongly coordinated with gazes at mothers’faces, patterns of gazing and smiling change. At 3months,infants tend to begin and end their smiles within gazes atthe parent’s face; that is, infants’ early expressions of

positive emotion are dependent on visual contact withthe parent. At 6months, infants tend to gaze at mother’sface, smile, gaze away, and only then end the smile.

p0270Gazing away from the parent during smiling appearsto be an early mechanism of emotion and arousal regula-tion. Five-month-old infants playing peek-a-boo tend toavert their gaze from the mother’s face more frequentlyand for longer periods of time during stronger smiles andduring longer-lasting smiles. This suggests that strongerand longer-lasting smiles involve more intense affec-tively positive arousal which infants regulate by gazingaway from their parents’ faces. In addition, smiles inwhich infants gaze away before the peak of the smile isreached may have a ‘coy’ quality which leads naı̈ve obser-vers to perceive some of these smiles as communicatingshyness. These developmental patterns of gazing at andaway from the parent’s face are the context in whichsmiling develops during face-to-face interactions.

p0275As infant smiling increases between 2 and 6months,infants also become more active participants in smilingdialogues. Infants’ tendency to smile in response tomothers’ smiles increases with age as does infants’ pro-pensity to initiate smiles – even in the absence of aprevious maternal smile. The age at which infants becomereliably responsive to their mother’s smiles and the rangeof responsivity between different infants and mothers is atopic of active research.

s0165The development of different types of smiling

p0280Considered as a whole, infant smiling during face-to-faceinteraction increases between 2 and 6months. Differenttypes of smiling, however, show different patterns ofdevelopment. Simple smiles that involve neither eyeconstriction nor mouth opening show a nonspecific risein different interactive periods (see Figure 4). By con-trast, the more emotionally positive open-mouth smilesinvolving eye constriction show a specific developmentalpattern. Between 2 and 6months, infants become increas-ingly likely to use open-mouth Duchenne smiling torespond to their smiling mothers. These combinationsmiles decline in periods when mothers are not smilingand infants are gazing elsewhere. In sum, highly positivetypes of smiling become selectively associated withmore positive periods of interaction. Infants’ increasingtendency to engage their smiling mothers with open-mouth cheek-raise smiling appears to index theiremerging capacity to fully participate in intensely joyfulinteractions.

p0285The period approaching 6months is one in whichinfants also become increasingly likely to gaze awayfrom mother during the course of a smile in order tocontrol their own arousal levels. As infants, then, becomemore capable of using very intense smiles to participate inhighly arousing social situations they also begin to exer-cise more control over the direction in which they smile.

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Infants are increasingly controlling their own positiveemotion by exercising control over their involvement inthe interchanges that lead to this positive emotion.

p0290 Another clue to the emotional meaning of infant smilesis the infants’ perceptions of the smiles of others. By4 months of age, infants can visually match their mothers’smiles with a matching vocalization and, by 5months,recognize the smile–vocalization pair posed by an experi-menter. These abilities suggest the infant’s appreciation ofthe affective meaning of the smiles of others is blossomingin the same period in which the infant is able to moreflexibly engage in his or her own intensely positive emo-tional expressions.

s0170 Smiling between 6 and 12 Months: TheDevelopment of Referential Smiling

p0295 In the first half year of life, infant emotional expressionduring face-to-face interactions reflects a primary, nonre-flective communication of immediate experience. In thesecond half of the first year of life, infant smiling takes ona qualitatively new form as smiling is integrated intointentional communications. We begin by reviewing theform of infant smiling and laughter during this period,examine smiles associated with walking, mastery smiles,and then turn to the development of smiling in intentionalcommunications.

s0175 The development of different types of smiling,

laughter, and mastery smiles

p0300 Between 6 and 12 months of age, strong smiles combiningthe Duchenne marker and mouth opening occur in themidst of positive and exciting periods of interaction suchas physical play with a parent. Simple smiling without

these features predominates both during the preparatoryphases of active games (e.g., getting ready to tickle) andduring slower-paced activities (e.g., book reading). Whilegames such as tickle become more potent elicitor ofsmiles between 6 and 12months, it is not clear if therelative frequency of different types of smiling – or theirassociation with different types of elicitors – changes inthis period. The conditions that elicit laughter, however,change developmentally.

p0305Laughter is a smile-linked vocalization indexingintense positive emotion and arousal that becomes morecommon between 6 and 12months. During this period,physical stimulation such as pat-a-cake remains potentelicitors of laughter even as infants become more likelyto laugh in response to social games such as peek-a-boo.One factor in this development is that infants are becomeincreasingly active agents in social games (e.g., moving theparent’s hands in peek-a-boo and eventually hiding theparent) and eventually become full partners in producingtheir own smile- and laugh-inducing experiences.

p0310Cognitive differentiation theory holds that mastery ofa challenging task is intrinsically rewarding. In support,infants approaching 1 year of age engage in more smilingand laughing when engaging in newly acquired capacitiessuch as pulling to stand than when engaging in morepracticed tasks such as pulling to sit.

p0315Smiling is linked to the developmental achievementsof the toddler and young child. For early walkers (before12months), the onset of walking is associated with anincrease in infant positive emotional expressions such assmiling. Walking onset is also, however, associated with adecrease in maternal expressions of positive affect to theearly walker and increases in interpersonal struggles. This‘testing of the wills’ may reflect the toddler’s delight in the

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f0020 Figure 4 (a) Open-mouth Duchenne smiling increases when infants are gazing at their mothers’ faces while their mothers are smiling.

It decreases when infants are not gazing at their mothers while their mothers are not smiling. (b) By contrast, simple smiling with

neither characteristic tends to increase irrespective of where the infant is gazing and whether or not the mother is smiling. All smilesare positive, but some smiles are more positive than others. All smiles are positive, but some smiles are more positive than others.

FromMessinger D, Fogel A, and Dickson KL (2001) All smiler are positive, but some smiles aremore positive than others.Developmental

Psychology 37(5): 642–653.

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experience of increased mobility and the mother’s work toensure that the young toddler stays safe despite theirincreased mobility. The mischievous smile may developaround this age as toddlers gaze back at a parent from adistance while smiling to ascertain the level of prohibitionor acceptance associated with a potential path of action.Such actions would reflect the toddler’s developing sec-ondary intersubjectivity, a topic to which we now turn.

s0180 Smiling in referential communication

s0185 Overview

p0320 In the period between 6 and 12months, infants and parentsincreasingly integrate objects into their play. Smiles tend tooccur in the context of coordinated joint engagement inwhich the infant actively shifts attention between a toy and asocial partner. When initiating joint attention, infants usegestures and gaze to refer to objects and events outside theinfant–partner dyad. Infant smiles are related to the com-municative meaning of these gestures and gazes. Infants aremore likely to smile during communications that show orshare an object than they are to smile during communica-tions that request an object or action. In sum, infants beginto smile at others with reference to particular objects orevents in what is known as triadic communication.

s0190 The development of referential communications

involving smiles

p0325 Between 6 and 9months, infant initiation of joint atten-tion by gazing between a toy and a responsive adultincreases. Yet even among infants who gaze between thetoy and an adult, the percentage who accompany this gazewith a smile rises between 6 and 9months. This suggeststhat integrating a smile into a gaze at a responsive adultindexes a more complex communicative message thangazing alone. Such smiles index the infant’s secondaryintersubjectivity, the infant’s awareness of the relationshipbetween the adult and toy. An additional index of theinfant’s secondary intersubjectivity involves the sequenceof smiling and gazing. The infant is aware not only of theparent, but increasingly aware of the parent’s attentionalstate with respect to an object or event.

p0330 Anticipatory smiles involve a specific sequence of smil-ing and then gazing at a partner that appears to index the

infant’s secondary intersubjectivity (see Figure 5). Infantsengage in anticipatory smiles when they smile at a toy orevent and then turn to gaze at an adult while continuing tosmile. The infant’s smile anticipates social contact andcommunicates pre-existing positive affect with anotherperson. It seems to communicate something like, ‘‘thatwas funny, wasn’t it.’’

p0335Infant anticipatory smiles increase between 8 and12 months. An infant’s likelihood of engaging in antici-patory smiling is associated with the infant’s generalcapacity to engage in intentional communications and tounderstand means–end relationships. This suggests thatanticipatory smiles index infants’ emerging ability tounderstand and refer to the relationship of an adult andan object. From a dynamic systems perspective, the real-time process of smiling and then referencing an object toanother suggests how positive emotion may motivate thedevelopment of early triadic communications.

s0195Smiling between 12–48 Months: Smiling amongToddlers and Preschoolers

p0340As toddlers become more mobile and young childrenbecome more involved in play with peers, many research-ers have neglected the observation of smiling, focusinginstead on other dimensions of social competence. From1 to 2 years of age, however, smiling and laughter remainrevealing elements of play with parents during a period inwhich toddlers become increasingly aware of the socialmeaning of the parents’ smiles Between 1 and 4 years,smiling is also an essential feature of the young child’sdeveloping peer play where it reveals emerging patternsof social affiliation. These two topics – smiling with par-ents and smiling with peers – are the focus of this section.

s0200Toddler smiling and laughter with the parent

p0345Infant comprehension of the smiles of others in socialreferencing paradigms provides evidence for the develop-ment of secondary intersubjectivity. In social referencingparadigms, infants are confronted with an ambiguousstimulus such as a moving mechanical object that mightbe interpreted as interesting or as threatening. Between12 and 18months of age, infants respond differentially to

f0025 Figure 5 Anticipatory smile. A 12-month-old infant gazes at an object (left), smiles at the object (middle), and gazes at theexperimenter while continuing to smile (right).

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adult smiles (and associated vocalizations) than to fear andneutral expressions. Infant’s interpret these adult smilesnot as direct expressions of joy (primary intersubjectivity),but as referential signals that the ambiguous situation isnonthreatening (secondary intersubjectivity).

p0350 The toddler’s developing understanding of pretenseis also related to maternal smiling. Mothers smile morewhen engaging in pretense activities with their 18-month-olds (e.g., pretending vs. really eating a snack). Toddlersalso give more clues that they understand that the acti-vities are pretend – they participate more and smile morethemselves – whenmothers smilemore. The 12–24-monthperiod also involves developments in dyadic laughter.When engaged in play during this period, infants andmothers begin and end their laughs increasingly closertogether in time. The members of the dyad appear tobecome increasingly responsive to the onset and offsetof one another’s positive communications, leading to theemergence of dyad-specific patterns of positive com-munication. Thus infant understanding of smiling as asocial signal (‘this is a pretend activity’) develops at thesame time as infants and mothers continue to evolvecomplex patterns of dyadic responsivity to each other’spositive emotion expressions.

s0205 Smiling in peer play

p0355 Peer play is an increasingly important context for socialdevelopment and smiling after 1 year. By 18months, level ofsmiling is linked to increased interaction with peers, parti-cularly when there is a relative absence of peer conflict.Additional evidence for the importance of peers involvesthree types of smiling identified among preschoolers.

p0360 A closed smile in which the teeth are covered that islikely related to simple smiling has been identified inpreschoolers. Closed smiling predominates in solitarycontexts and levels of closed smiling change little between2 and 4 years of age. Upper smiles and broad smiles andopen-mouth smiles show different patterns of occurrenceand development. Upper smiles display the upper teethand may include Duchenne smiles; broad smiles displayboth the upper and lower teeth and are likely to includeopen-mouth smiles. Upper and broad smiles occur insocial situations and are increasingly used with same-sexpeers between 2 and 4 years. Male children, in particular,are increasingly selective in directing broad smiles towardmale peers and not to female peers. Different types ofsmiling may, then, reflect and reinforce developing pat-terns of social affiliation such as the increasing sex segre-gation of young preschoolers.

p0365 With respect to more recent typologies of smilesamong preschoolers, by 3.5 years of age, stronger smilesare likely than weaker smiles to accompany success in agame. By 4.5 years, children tend to produce Duchennesmiles in games in which they produce – rather thansimply being shown – an interesting display. Mastery,

success, and failure during a given trial of a game arenot, however, always accurate predictors of smiling.Gaze at the examiner – or whomever the child is playingwith – remains a prepotent elicitor of smiling, whether thechild has failed or succeeded at the game. In the preschoolperiod, then, smiling continues to serve multiple masters.It expresses both joy at success and the happiness asso-ciated with interacting with a cooperative adult or peer.

s0210Smiling as an Index of DevelopmentalRisk and Disability

p0370Individual differences in smiling are meaningfully relatedto concurrent risk factors. Levels of smiling differ betweeninfants at risk for disturbed developmental outcomes andtypically developing infants. We review evidence for dif-ferences in smiling associated with prematurity, maternaldepression, and infants who are blind, infants with Downsyndrome, and infants with ‘autism spectrum disorders’ –emphasizing how such differences shed light on the dis-orders and conditions in question.

s0215Smiling in Premature Infants and the Infants ofDepressed Mothers

p0375Infants born prematurely spend less time than full-terminfants engaging in relatively strong open-mouth smilesduring face-to-face interactions and exhibit fewer strongsmiles during peek-a-boo gameswith an experimenter. Thislikely reflects the difficulties of many premature infants incoping with high levels of even positive emotional arousal.Maternal depression and maternal depressive symptom-atology, particularly when long-lasting or chronic, tend tobe associated with a reduction in infant smiling, at leastduring interactions with mother. This is likely to reflect alack of positive emotional responsivity to the infant on thepart of mothers with depressive symptomatology.

s0220Smiling in Blind Infants and Children

p0380The impact of environmental influences is evident in thedevelopment of smiling in blind infants. Blind infantsdemonstrate social smiling in response to social eventssuch as hearing a familiar voice and their smiling typicallyelicits a parental response. The frequency of these socialsmiles increases between 4 and 12months. However, thesmiles of blind infants are less regularly elicited and morefleeting than those of sighted infants. Blind infants, ofcourse, cannot enter into mutually reinforcing visuallymediated smiling exchanges with others, which maylimit the duration of their smiling. Lack of contingentvisual feedback to smiles is also likely to play a role inthe decrement in smiling observed in blind infants after2 or 3 years of age.

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s0225 Smiling in Infants with Down Syndrome

p0385 Infants with Down syndrome – trisomy – show delayeddevelopment of positive emotional expressivity with themost substantial delays evident among the most cogni-tively delayed infants and the infants with the most flaccidmuscle tone. Although levels of smiling are typically lowin infants with Down syndrome, these infants do showmastery smiles consonant with their cognitive level. Theyalso show the typical developmental pattern of smiling –first to auditory, then to visual and tactile, and then tosocial stimuli and activities.

p0390 Infants with Down syndrome show patterns of indis-criminate smiling whose cognitive and affective baseshave not been adequately specified. Infants with Downsyndrome direct open-mouth Duchenne smiles both totheir mothers and to toys, whereas typically developinginfants direct these smiles only to mother. Infants withDown syndrome also do not show decrements in smilingwhen their mothers adopt a still-face as dramatic as thedecrements of typically developing infants. It remains tobe seen whether such indiscriminate smiling is associatedwith the level of cognitive functioning of individualinfants with Down syndrome.

s0230 Smiling in Children with Autism SpectrumDisorders

p0395 While children with Down syndrome show indiscriminatesmiling, children with autism spectrum disorders (ASD)show deficits in facial expressivity frequently includinglow levels of smiling. Low levels of smiling are associatedwith deficits in initiating joint attention and are particu-larly salient when children with ASDs are oriented towardan adult. These effects are evident as early as 12 monthsamong infants who will later be diagnosed with an ASD.Even among infants at risk for autistic symptomatologybecause they are siblings of children with an ASD, levelsof neutral affect are higher in early face-to-face interac-tions than among other infants. Smiling in children withASDs reflects a deficit in the degree to which face-to-facecontact with others is rewarding that may have cascad-ing repercussions for the social development of affectedchildren.

s0235 Developmental Continuity in Smiling:Predicting Social Competence

p0400 Individual differences in smiling are meaningfully relatedto subsequent developmental outcomes. This section isconcerned with the continuity of early expressions ofpositive emotion and the association between earlysmiling and later indices of social competence. We begin

with a discussion of smiling and security of attachmentand other indices of social competence, turn to geneticand environmental influences on smiling, and end witha discussion of interactive smiling and its impact onsocialization.

s0240Smiling and Attachment

p0405Infants who smile when their parent adopts a nonrespon-sive still-face have a tendency to develop socially appro-priate relationships. They are perceived by their parentsas having fewer externalizing behaviors (such as beingloud and rough) 1 year later than infants who do notsmile during the still-face, and may be more likely todevelop secure attachments.

p0410Infants whose level of smiling during face-to-face playwith the parent rises between 2 and 8months are morelikely to be classified as securely attached than otherinfants. Similarly, smiling with the parent in play sessionsaround 18months of age is associated with concurrentattachment security. It may be that regular smiling inter-actions in which the parent helps the infant modulatetheir level of positive arousal are a route to the develop-ment of a secure attachment relationship. This modula-tion involves not only responding positively to the infants’smiles but being responsive to the infant’s need to lookaway after intense smiling bouts. This allows infants tocalm themselves and then look back (and perhaps smile)at the parent.

s0245Face-to-Face Smiling, Joint Attention Smiling,and Social Competence

p0415Early social smiling in face-to-face interaction witha parent positively predicts ‘anticipatory smiling’, atendency to communicate positive affect about an objectto an adult tester. In addition, highly sensitive maternalcaregiving predicts a more general measure of infantsmiling at any point during an infant joint attentionepisode. It appears that infants’ experience with early-rewarding social stimuli contributes to a later predilectionto initiate positive communicative referencing with others.

p0420Anticipatory smiling toward 1 year of age predictsparent-reported social expressivity and social competencescores at 30months. Positive affect sharing indexed byanticipatory smiling may be a developmentally focalactivity that is predicted by early social smiling and pre-dicts subsequent social expressivity and competence.Likewise, infant Duchenne smiling during reunions withmother in the Strange Situation predicts parent ratings ofextraversion and openness to experience when childrenare 3.5 years of age. In sum, positive emotion expressionelicits positive responses from social partners that fosterlater sociability and social competence.

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s0250 Smiling: Genetic and Environmental Effects

p0425 Parent reports on dimensions of infant temperamentinvolving questions about infant smiling and laughterreveal the influence of both genetic and environmentaleffects. This contrasts with negative emotion expression,which showers higher genetic and lower environmentaleffects. Shared environmental effects in positive emotionexpression point to possible socialization effects in factorsthat determine parent perceptions of level of smiling. Thismay mean that more emotionally positive infant–parentinteractions influence future levels of infant smiling andpositive emotional expression.

s0255 Developmental Continuity in Smiling

p0430 Infant reaction to standardized elicitors of smiling andother positive emotional expressions such as a puppetshow and jack-in-the-box show moderate developmentalstability between 1 and 3 years of age. Infants who engagein extremely high levels of smiling, positive vocalizations,and motor movement at 4months in response to a mobileand auditory stimuli show different developmental pat-terns than infants who are nonresponsive or show moreemotionally negative reactions. The infants who displayearlier smiling are less behaviorally inhibited in unfamil-iar situations over the first 2 years of life than the otherinfants. They continue to show a more exuberant temper-amental style at 4 years when they are more likely to talkand engage with peers.

s0260 Concurrent Validity of Smiling to Social Stimuli

p0435 Infant smiles to social stimuli such as peek-a-boo gameswith examiners and infant smiles to nonsocial stimuli suchas a jack-in-the-box appear to have different meanings.Only infant smiles to social stimuli are associated withinfant positive emotion expression in the parent–childrelationship and with parent ratings of their children’sday-to-day positive emotion. Infant smiling in theparent–child relationship is in turn associated with latersocial competence.

s0265 Predictive Validity of Interactive Smiling

p0440 Through smiling in face-to-face interactions infants cometo engage in simultaneous, reciprocal, and mutually enjoy-able exchanges. Affecting and being affected by the posi-tive emotional expression of the parent may lead infants toexperience the happiness of others as essential to their ownhappiness. In support, shared infant–mother positiveemotional expressions such as smiles – when they occurin conjunction with maternal responsivity to infant – are

associated with two indices of social competence:children’s internalization of social norms (obeying therules) and committed compliance to maternal directives(cleaning up without reminders). In this way, experiencesof affectively positive responsivity emerge from socialinteraction and shape the infant’s developing socialcompetence into childhood.

See also: Attachment (00012); Autism SpectrumDisorders (00016); Emotion Regulation (00055);Imitation and Modeling (00082); Newborns (00112);Self Knowledge (00139); Humor (00078); IntermodalPerception (00086).

Suggested Readings

Aksan N and Kochanska G (2004) Heterogeneity of joy in infancy.Infancy 6(1): 79–94.

Barrett LF and Wager TD (2006) The structure of emotion: Evidencefrom neuroimaging studies. Current Directions in PsychologicalScience 15(2): 79–83.

Cohn JF and Tronick EZ (1987) Mother infant face-to-face interaction:The sequence of dyadic states at 3, 6, and 9 months. DevelopmentalPsychology 23(1): 68–77.

Fox NA and Davidson RJ (1988) Patterns of brain electrical activityduring facial signs of emotion in 10 month old infants. DevelopmentalPsychology 24(2): 230–236.

Kochanska G (2002) Mutually responsive orientation between mothersand their young children: A context for the early development ofconscience. Current Directions in Psychological Science 11:191–195.

Messinger D, Fogel A, and Dickson KL (2001) All smiles are positive, butsome smiles are more positive than others. DevelopmentalPsychology 37(5): 642–653.

Sroufe LA and Waters E (1976) The ontogenesis of smiling and laughter:A perspective on the organization of development in infancy.Psychological Review 83: 173–189.

Striano T and Berlin E (2005) Coordinated affect with mothers andstrangers: A longitudinal analysis of joint engagement between 5 and9 months of age. Cognition and Emotion 19(5): 781–790.

Venezia M, Messinger DS, Thorp D, and Mundy P (2004) Thedevelopment of anticipatory smiling. Infancy 6(3): 397–406.

Waller BM and Dunbar RIM (2005) Differential behavioural effects ofsilent bared teeth display and relaxed open mouth display inChimpanzees (Pan troglodytes). Ethology 111(2): 129–142.

Weinberg MK and Tronick EZ (1994) Beyond the face: An empiricalstudy of infant affective configurations of facial, vocal, gestural, andregulatory behaviors. Child Development 65(5): 1503–1515.

Relevant Websites

http://face-and-emotion.com – A site devoted to the human face,Dataface (contains information on the anatomically based FacialAction Coding System for the measurement of smiles and otherexpression).

http://www.psych.utah.edu – Alan Fogel’s website.http://www-2.cs.cmu.edu – Automated Face Analysis at the Carnegie

Mellon University, Robotics Institute.http://www.psy.miami.edu – Daniel Messinger’s website.

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Non-Print Items

Abstract:Early smiles are a prototypical expression of joy and a window on the development of positive emotion. Smiles elicitpositive emotion and engagement in others, a process that contributes to the development of joy and socialcompetence in the young child. Infants express different intensities and qualities of positive emotion throughalterations in the temporal and facial dynamics of their smiling and through the incorporation of other expressiveactions such as laughter and jumping up and down. Through the first two years of life, infant smiles and laughterbecome increasingly social and affectively intense, and increasingly used in referential communications aboutobjects; between 2 and 4 years, smiles reflect the social structure of peer interactions. Difficulties with smiling inearly interactions reflect a variety of risk conditions, while emotionally positive and responsive interactions can indexoptimal developmental trajectories.

Keywords: Affect; Arousal; Attachment; Development; Emotion; Face-to-face; Infant; Interaction; Joy; Mastery;Toddler

Author and Co-author Contact Information:

D MessingerFlipse Psychology Annex, PO Box 249229Coral Gables,FL 33124-0721USA+1 305-284-8443+1 305-284-4795dmessinger@miami.edu

Biographical Sketch for Online Version

Daniel S. Messinger was born in El Reno, Oklahoma, earned his Masters at the University of Chicago in 1989 and his PhD at the

University of Utah in 1994, where he studied with Alan Fogel. He took a position at the University of Miami in Pediatrics in 1993and a position in Psychology in 1999. Dr. Messinger investigates a range of basic and applied developmental questions. He isparticularly interested in real-time emotional interaction and its role in development. His current work involves infants at-risk

for autism and the measurement of emotional dynamics.

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