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From symmetry to asymmetry? The development of smile

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Abstract

The left side of the face has been reported to be more expressive than the right side in human adults. The developmental origin of this lateralization, however, is unknown. Chimeric still composite photos of smiling faces of 0-5 months (n=61), 6-12 months (n=67) old infants, 3-8 years old children (n=78), and 32 adults (>18 years) were rated for intensity by 90 judges. The results showed left-hemiface dominance in adults only, and not in infants or children. It can be speculated that this early functional symmetry may evolutionarily increase attractiveness and elicits secure bonding and care.

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... Otherwise, there are numerous studies evaluating facial soft tissue asymmetry, which has an important place in the description of facial beauty. In addition, smile symmetry in smile aesthetics has an important role in aesthetic perception [15,16]. A symmetry of the smile is influenced by many factors, including arch form and the position of the teeth on the arch [15]. ...
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This study aimed to evaluate social smile asymmetry in patients with unilateral impacted maxillary canine on 3D stereophotogrammetric images. The 3D social smile images of participants with unilateral impacted maxillary canine (n:20) and without impaction as a control group (n:20) were included. The images were recorded with a hand-held 3D stereophotogrammetry device (Fuel3D® Scanify®) and Geomagic Essentials 2 reverse engineering software were used for analyses. After the orientation process of the 3D records, the tissues around the smile area were divided into five morphological regions: cheek, upper lip lateral and medial, and lower lip lateral and medial. The deviation margins in the negative and positive directions for the 95% mesh rate and the total percentages of meshes between − 0.5- and + 0.5-mm deviations were calculated. ICC, paired samples t test, independent samples t test, and the Mann–Whitney U test were used for statistical analyses. In individuals with impacted canine, the amount of maximum positive deviation in the upper lip medial was 5.64 mm ± 1.46 and maximum negative deviation was − 4.6 mm ± 1.17. In the control group, mean of deviation limits for all parameters was less than 1.19 mm ± 2.62, while in individuals with unilateral impacted maxillary canine, the maximum value was 8.34 mm ± 2.23. The mesh percentage between − 0.5 and 0.5-mm deviations was over 95% in all morphological areas in the control group, while in the impacted canine group, the number of meshes within the specified deviation limits was less than 95%. Individuals with unilateral impacted maxillary canine exhibit greater asymmetry in social smile compared to the control group, with the asymmetry being most prominent near the corners of the mouth and cheeks. Amount of asymmetry was higher in impaction group compared to the control group in social smile. The quantification of a possible smile asymmetry due to the impacted canine is crucial for the diagnosis and treatment planning of orthodontic and/or orthognathic cases for ideal aesthetic results. Hence, smile asymmetry should not be overlooked and should be considered in diagnosis and treatment planning.
... Studies with composite faces presenting the same anatomical hemi-faces (i.e., left-left; right-right) have shown that anatomical left-left composites of faces are rated by beholders as more emotionally expressive (Indersmitten and Gur 2003;Nagy 2012). More recently, studies of portraits, photos and selfies demonstrate that the subjects represented in the images tend to display the more expressive left hemi-face (for portraits, see Humphrey and McManus 1973;McManus and Humphrey 1973;Grusser et al. 1988;Lindell 2013a,b;Powell and Schirillo 2011; White 2019; for photos, see Nicholls et al. 1999Nicholls and Roberts 2002; for selfies, see Bruno and Bertamini 2013;Bruno et al. 2015Bruno et al. , 2016Lindell 2015Lindell , 2017Manovich et al. 2017) and that beholders tend to rate the left cheek biased faces as more emotionally expressive (Low and Lindell 2016;Galea and Lindell 2016;Nicholls et al. 2004). ...
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The topic of the human face is addressed from a biocultural perspective, focusing on the empirical investigation of how the face is represented, perceived, and evaluated in artistic portraits and self-portraits from the XVth to the XVIIth century. To do so, the crucial role played by the human face in social cognition is introduced, starting from development, showing that neonatal facial imitation and face-to-face dyadic interactions provide the grounding elements for the construction of intersubjective bonds. The neuroscience of face perception is concisely presented and discussed, together with the psycho-physics of face perception and gaze exploration, introducing the notions of the left visual field advantage (LVFA) and the left gaze bias (LGB). The results of experiments on the perception and the emotional and aesthetic rating of artistic portraits and self-portraits are reported, showing that despite participants' inability to tell self-portraits and portraits apart, greater emotional, communicative-social, and aesthetic ratings were attributed to self-portraits. It is concluded that neuroscience and experimental aesthetics can contribute to better understand the human face, hence to better understand ourselves.
... Smaller or larger values can also be used. Moreover, since we used unilateral hemifacial arrays, additional information could be derived by bilateral masks for healthy and pathological conditions that are relevant to facial symmetry [55,56]. ...
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Objective. Human facial muscle activation underlies highly sophisticated signaling mechanisms that are critically important for healthy physiological function. Accordingly, the necessity to analyze facial muscle activation at high-resolution and in a non-invasive manner is important for the diagnosis and treatment of many medical conditions. However, current clinical examination methods are neither precise nor quantitative. Approach. Wearable, multi-channel surface electromyography can provide a solution to this yet unmet challenge. Here, we present the design and testing of a customized surface electromyography electrode array for facial muscle mapping. Main results. Muscle activation maps were derived from repeated voluntary facial muscle activations. A customized independent component analysis algorithm and a clustering algorithm were developed to identify consistent building block activation patterns within and between participants. Finally, focusing on spontaneous smile analysis and relying on the building block mapping, we classified muscle activation sources, revealing a consistent intra-subject activation and an inter-subject variability. Significance. The herein described approach can be readily used for automated and objective mapping of facial expressions in general and in the assessment of normal and abnormal smiling in particular.
... Studies with composite faces presenting the same anatomical hemi-faces (i.e. left-left; right-right) have shown that anatomical left-left composites of faces are rated as more emotionally expressive (Indersmitten and Gur, 2003;Nagy, 2012). More recently, studies of portraits, photos and selfies demonstrate that the subjects represented in the images tend to display the more expressive left hemi-face (portraits: Humphrey and McManus, 1973;McManus and Humphrey, 1973;Grüsser et al., 1988;Lindell, 2013b;Powell and Schirillo, 2009;White, 2019;photos: Nicholls et al., 1999photos: Nicholls et al., , 2002aHarris and Lindell, 2011; selfies: Bruno and Bertamini, 2013;Bruno et al., 2015Bruno et al., , 2016Lindell, 2015Lindell, , 2017Manovich et al., 2017) and that participants tend to rate the left cheek biased faces as more emotionally expressive (Low and Lindell, 2016;Lindell et al., 2015;Harris and Lindell, 2011;Galea and Lindell, 2016;Nicholls et al., 2004). ...
Article
Studies on the lateralization of facial perception and the asymmetry of facial emotional expressions date back to the 19th century. Several left-side biases have been identified: greater expressivity of the left side of the face, a left cheek bias (i.e. a preference to display one’s left cheek), a left visual field advantage (i.e. a preference and improved performance when stimuli are presented in the left visual field), a left gaze bias (i.e. a preference to direct and to spend more time looking at the left side of centrally presented faces, i.e. the anatomical right side). The simultaneous occurrence of these left-side biases, however, has hardly been studied. Thus, we recorded participants’ visual scan-paths and emotional intensity ratings of the depicted faces of pre-19th century self-portraits (i.e. anatomical left side of the face in the left visual field), portraits (i.e. anatomical left side of the face in the right visual field), and their mirror-reversed formats. Self-portraits evoked greater emotional intensity ratings and shorter latencies of the first fixation than portraits, regardless of their format. In addition, for self-portraits the duration of the first fixation was longer for the anatomical left hemi-face. We hypothesize that the observation of self-portraits may arouse greater sensorimotor engagement in the observer as a result of the greater sensorimotor engagement of the artist while painting them.
... 29 With regard to smile symmetry, it has been shown that the smile tends to become more asymmetrical with age, with children aged 3-8 years old showing more symmetrical smiles than adults. 30 Other authors have also found that the smile shows various amounts of asymmetry in the x, y and z planes and that asymmetry increases specifically at the oral commissures. 31 Moreover, posed smiles have been found to be more asymmetrical than spontaneous smiles. ...
Article
Background Functional appliances have skeletal and dentoalveolar treatment effects, but knowledge on their effect on facial expressions is limited. Objective To analyse changes in facial expressions, using three‐dimensional (3D) mimic muscle evaluation, in growing children with Class II malocclusion and large overjet, undergoing functional appliance treatment. Methods Fifteen growing children with Class II division 1 malocclusion, selected prospectively, had dynamic 3D recordings of facial expressions prior to and 12 months after commencing functional appliance treatment. Facial expressions recorded were smile and lip pucker, and the movements of the oral commissures were analysed, as well as mouth width and its symmetry. A control group of fifteen age‐ and sex‐matched growing children without immediate need for orthodontic treatment had similar recordings prior to and after a 12‐month observation period. Results In the treatment group, the Class II malocclusion in all children improved after 12 months of functional appliance wear. With regard to movements of the oral commissures, the initial recordings of the treatment group did not show any significant differences to the control group for neither smile nor lip pucker. Differences were noted however when looking at mouth width asymmetry, where this tended to become more symmetrical in the functional appliance treatment group, during rest and during smiling, while it became more asymmetrical in the untreated control group. Conclusion The use of removable functional appliances in children with Class II division 1 malocclusion may have a positive effect on mouth width symmetry when smiling, making it more symmetrical. This article is protected by copyright. All rights reserved.
... The asymmetry of the face might be related to the brain lateralization, in which the right hemisphere plays a dominant role in emotion processing [14,47,48]. There is a dominance of the facial left side for emotion expressions, due to its innervation by the right hemisphere, which is dominant for facial emotional expression [49] ...
Article
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Physiological signals may be used as objective markers to identify emotions, which play relevant roles in social and daily life. To measure these signals, the use of contact-free techniques, such as Infrared Thermal Imaging (IRTI), is indispensable to individuals who have sensory sensitivity. The goal of this study is to propose an experimental design to analyze five emotions (disgust, fear, happiness, sadness and surprise) from facial thermal images of typically developing (TD) children aged 7–11 years using emissivity variation, as recorded by IRTI. For the emotion analysis, a dataset considered emotional dimensions (valence and arousal), facial bilateral sides and emotion classification accuracy. The results evidence the efficiency of the experimental design with interesting findings, such as the correlation between the valence and the thermal decrement in nose; disgust and happiness as potent triggers of facial emissivity variations; and significant emissivity variations in nose, cheeks and periorbital regions associated with different emotions. Moreover, facial thermal asymmetry was revealed with a distinct thermal tendency in the cheeks, and classification accuracy reached a mean value greater than 85%. From the results, the emissivity variations were an efficient marker to analyze emotions in facial thermal images, and IRTI was confirmed to be an outstanding technique to study emotions. This study contributes a robust dataset to analyze the emotions of 7-11-year-old TD children, an age range for which there is a gap in the literature.
... The early appearance of affiliation smiles may reflect humans' strong propensity toward cooperation and fairness [113]. Furthermore, asymmetrical expressionsa critical element of dominance smiles [60] are seen in adults, but not children between the ages of 3 and 8 years [114]. This finding suggests that dominance smiles may not be deployed until later in development, likely emerging during adolescence. ...
Article
The human smile is highly variable in both its form and the social contexts in which it is displayed. A social-functional account identifies three distinct smile expressions defined in terms of their effects on the perceiver: reward smiles reinforce desired behavior; affiliation smiles invite and maintain social bonds; and dominance smiles manage hierarchical relationships. Mathematical modeling uncovers the appearance of the smiles, and both human and Bayesian classifiers validate these distinctions. New findings link laughter to reward, affiliation, and dominance, and research suggests that these functions of smiles are recognized across cultures. Taken together, this evidence suggests that the smile can be productively investigated according to how it assists the smiler in meeting the challenges and opportunities inherent in human social living.
... It is reported that the right hemisphere of the brain is more dominant and that the left side of the face is more expressive than the right during the smile. 26 Sawyer et al. 23 investigated different smile types threedimensionally and reported that there was a maximum 108 directional difference between the right and left morphological points at a range of 0 to 6 mm, and they almost moved symmetrically. Based on the findings of the present study, the difference (95% Cl) between the amounts of movement in the right and left Com during the smile varied within an insignificant range. ...
Article
Objective: To evaluate the social smile symmetry using three-dimensional (3D) stereophotogrammetric images. Materials and methods: The study was conducted with 3D facial images of 30 individuals (age range 13-25 years). The rest position was considered as the reference image and the social smile image was aligned on this image using the best-fit alignment method. The spatial differences between the same points established on both images using 3D analyses were determined for right and left points in X, Y, and Z planes. Results: The highest difference related to spatial distance in right and left points was -0.56 mm (95% confidence interval [CI], -1.19, 0.06 mm) between right and left commissure (Com) points. The difference was not significant, and the Bland-Altman upper and lower limits were -3.85 mm and 2.71 mm, respectively. The highest difference for the transversal plane was found in Com points, similarly to the spatial distance (mean: 0.50 mm, 95% CI, -2.62, 1.02 mm). The differences between the changes in the left and right points in the Y and Z plane were not significant (P > .05). Conclusions: The social smile was observed to show asymmetry in varying amounts in the different directions. Asymmetry increases in some cases, specifically for the corners of the mouth.
... 20,[27][28][29] However, studies show that even normal smiles are asymmetric and therefore may decrease attractiveness. 30 This smiling paradox may be answered by studies that indicate the degree of asymmetry in the average normal smile is not detected by casual observers. Thus, smiling may increase perceived facial symmetry and attractiveness ratings. ...
Article
Objectives/HypothesisDetermine the effect of facial reanimation surgery on observer-graded attractiveness and negative facial perception of patients with facial paralysis. Study DesignRandomized controlled experiment. Methods Ninety observers viewed images of paralyzed faces, smiling and in repose, before and after reanimation surgery, as well as normal comparison faces. Observers rated the attractiveness of each face and characterized the paralyzed faces by rating severity, disfigured/bothersome, and importance to repair. Iterated factor analysis indicated these highly correlated variables measure a common domain, so they were combined to create the disfigured, important to repair, bothersome, severity (DIBS) factor score. Mixed effects linear regression determined the effect of facial reanimation surgery on attractiveness and DIBS score. ResultsFacial paralysis induces an attractiveness penalty of 2.51 on a 10-point scale for faces in repose and 3.38 for smiling faces. Mixed effects linear regression showed that reanimation surgery improved attractiveness for faces both in repose and smiling by 0.84 (95% confidence interval [CI]: 0.67, 1.01) and 1.24 (95% CI: 1.07, 1.42) respectively. Planned hypothesis tests confirmed statistically significant differences in attractiveness ratings between postoperative and normal faces, indicating attractiveness was not completely normalized. Regression analysis also showed that reanimation surgery decreased DIBS by 0.807 (95% CI: 0.704, 0.911) for faces in repose and 0.989 (95% CI: 0.886, 1.093), an entire standard deviation, for smiling faces. Conclusions Facial reanimation surgery increases attractiveness and decreases negative facial perception of patients with facial paralysis. These data emphasize the need to optimize reanimation surgery to restore not only function, but also symmetry and cosmesis to improve facial perception and patient quality of life.
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In an era in which society is becoming more and more based on knowledge, and digital technologies have become indispensable for carrying out daily activities, social change becomes a problem whose solution cannot wait postponement. This paper intends to present a framework on the importance of developing social innovation labs as instruments for achieving social change, social innovation bringing countless benefits in the individuals’ life. The methodology used for conducting this research is bibliographical – therefore we chose to study the research of specialists in the field, both from Romania and abroad, and empirical – achieved by constructing a case study on best practices examples of these living labs. Through social innovation labs, individuals form connections with each other, they mobilize in order to achieve a common goal – to create a better future. Research shows that social innovation labs behave like normal labs, thus they invent and experiment on finding solutions for the challenges of today’s world. Often, they generate promising solutions. However, in order for those solutions to be successful, the fact that the human resource is the crucial element should not be forgotten. Hence, individuals’ ability and willingness to cooperate should be considered, not only by electronic means, but also through traditional methods of participation in the process of social change through innovation. [http://editurauranus.ro/holistica/wp-content/uploads/2014/01/cuprins_nr_2_2016.pdf]
Chapter
Recent work in social robotics, which is aimed both at creating an artificial intelligence and providing a test-bed for psychological theories of human social development, involves building robots that can learn from ‘face-to-face’ interaction with human beings — as human infants do. The building-blocks of this interaction include the robot’s ‘expressive’ behaviours, for example, facial-expression and head-and-neck gesture. There is here an ideal opportunity to apply Wittgensteinian conceptual analysis to current theoretical and empirical work in the sciences. Wittgenstein’s philosophical psychology is sympathetic to embodied and situated Artificial Intelligence (see Proudfoot, 2002, 2004b), and his discussion of facial-expression is remarkably modern. In this chapter, I explore his approach to facial-expression, using smiling as a representative example, and apply it to the canonical interactive face robot, Cynthia Breazeal’s Kismet (see e.g. Breazeal, 2009, 2002). I assess the claim that Kismet has expressive behaviours, with the aim of generating philosophical insights for AI.
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Purpose: Our understanding of who is beautiful seems to be innate but has been argued to conform to mathematical principles and proportions. One aspect of beauty is facial shape that is gender specific. In women, an oval facial shape is considered attractive. Objective: To study the facial shape of beautiful actors, pageant title winners, and performers across ethnicities and in different time periods and to construct an ideal oval shape based on the average of their facial shape dimensions. Methods: Twenty-one full-face photographs of purportedly beautiful female actors, performers, and pageant winners were analyzed and an oval constructed from their facial parameters. Results: Only 3 of the 21 faces were totally symmetrical, with the most larger in the left upper and lower face. The average oval was subsequently constructed from an average bizygomatic distance (horizontal parameter) of 4.3 times their intercanthal distance (ICD) and a vertical dimension that averaged 6.3 times their ICD. Conclusion: This average oval could be fitted to many of the individual subjects showing a smooth flow from the forehead through temples, cheeks, jaw angle, jawline, and chin with all these facial aspects abutting the oval. Where they did not abut, treatment may have improved these subjects.
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Since the discovery of facial asymmetries in emotional expressions of humans and other primates, hypotheses have related the greater left-hemiface intensity to right-hemispheric dominance in emotion processing. However, the difficulty of creating true frontal views of facial expressions in two-dimensional photographs has confounded efforts to better understand the phenomenon. We have recently described a method for obtaining three-dimensional photographs of posed and evoked emotional expressions and used these stimuli to investigate both intensity of expression and accuracy of recognizing emotion in chimeric faces constructed from only left- or right-side composites. The participant population included 38 (19 male, 19 female) African-American, Caucasian, and Asian adults. They were presented with chimeric composites generated from faces of eight actors and eight actresses showing four emotions: happiness, sadness, anger, and fear, each in posed and evoked conditions. We replicated the finding that emotions are expressed more intensely in the left hemiface for all emotions and conditions, with the exception of evoked anger, which was expressed more intensely in the right hemiface. In contrast, the results indicated that emotional expressions are recognized more efficiently in the right hemiface, indicating that the right hemiface expresses emotions more accurately. The double dissociation between the laterality of expression intensity and that of recognition efficiency supports the notion that the two kinds of processes may have distinct neural substrates. Evoked anger is uniquely expressed more intensely and accurately on the side of the face that projects to the viewer's right hemisphere, dominant in emotion recognition.
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The development of functional brain asymmetry during childhood is confirmed by changes in cerebral blood flow measured at rest using dynamic single photon emission computed tomography. Between 1 and 3 years of age, the blood flow shows a right hemispheric predominance, mainly due to the activity in the posterior associative area. Asymmetry shifts to the left after 3 years. The subsequent time course of changes appear to follow the emergence of functions localized initially on the right, but later on the left hemisphere (i.e. visuospatial and later language abilities). These findings support the hypothesis that, in man, the right hemisphere develops its functions earlier than the left.
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Asymmetries of the smiling facial movement were more frequent in deliberate imitations than spontaneous emotional expressions. When asymmetries did occur they were usually stronger on the left side of the face if the smile was deliberate. Asymmetrical emotional expressions, however, were about equally divided between those stronger on the left side of the face and those stronger on the right. Similar findings were obtained for the actions involved in negative emotions, but a small data base made these results tentative.
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Subjects rated the intensity of emotional expressiveness of left side, right side and original orientation composite human faces, expressing seven distinct emotions. Left side composites were judged to be more emotionally intense than right side composites. The finding points to hemispheric asymmetry in the control of emotional expression and has implications for the role of emotional expression in communication.
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The developmental origins of behavioural asymmetries, in particular handedness, have aroused considerable interest and debate. Until now such behavioural asymmetries have only been reported after birth. Here we report the existence of handedness before birth, expressed in terms of thumb-sucking by the fetus. Ultrasound observations of fetuses from 15 weeks to term revealed a marked bias for sucking the thumb of the right hand. This preference appears to be maintained throughout pregnancy, is unrelated to fetal position in utero but correlates with head position preference in the supine newborn. The findings indicate that handedness is present prior to birth and the implications of this for the development of laterality are discussed.
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The purpose of this report was to examine facial asymmetry during the expression of positive and negative emotions. In addition, methodological factors in the study of facial asymmetry were considered. Subjects were 16 neurologically-healthy right-handed adult males, videotaped while posing eight facial expressions (positive and negative) under two conditions (verbal command and visual imitation). Separate asymmetry ratings of the two sides of the face were made by judges viewing normal or mirror-reversed versions of the videotape. There were no effects of valence, condition, or videotape orientation on the asymmetry ratings, and, in general, expressions were produced significantly more intensely on the left than the right side of the face. This finding is consistent with the hypothesis that the right cerebral hemisphere is dominant for the expression of facial emotion of both valences.
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While strictly verbal cognitive tasks showed a strong left-hemisphere dominance, the presence of visualization and emotion in cognitive tasks resulted in increased involvement of the right hemisphere in motor control of speech as measured by mouth asymmetry. Spontaneous smiles showed right-hemisphere dominance. Lateral eye movements showed an unexpected shift to left gaze during speech which may suggest a dual task interference between speech and gaze motor control.
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A high proportion of normal subjects have speech expression controlled predominantly by the left hemisphere. Since the left hemisphere also has stronger control of the right side of the lower face, it might be expected that normal subjects would show a right-sided asymmetry in mouth opening during speech. This hypothesis was tested by measuring lip opening in 196 subjects. Of these, 150 (76%) showed greater right-side opening. This tendency was found for males, females, left- and right-handers in four experiments using two different techniques. Mouth asymmetry during speech may provide an indication of which hemisphere is dominant for expressive speech.
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Facial asymmetry or “facedness” was reliably rated for nine different videotaped facial expressions of emotion, produced by 51 adults, and was significantly left-sided. This finding was related to right hemisphere dominance for emotion and for facial movement. No overall differences occurred for expression type or sex and handedness of subjects, but there were interactions.RésuméL'asymétrie faciale (“facedness”) était liée de façon fiable pour 9 expressions faciales différentes, réalisées par 51 adultes et se manifestait significativement sur le côté gauche. Cette constatation était liée à la dominance hémisphérique droite pour les émotions et le mouvement de la face. On ne constatait pas de différence générale sur le type d'expression, le sexe et la préférence manuelle des sujets, mais il existait des interactions entre ces facteurs.ZusammenfassungGesichtsasymmetrie oder “Gesichtigkeit” wurde zuverlässig für 9 unterschiedliche, auf Video aufgenommene Arten von Gesichtsausdruck bewertet, die von 51 Erwachsenen produziert wurden. Die Asymmetrie was signifikant linksseitig. Der Befund war in Beziehung zur rechtshemisphärischen Überlegenheit für Emotion und Gesichtsausdruck. Es fanden sich keine globalen Unterschiede für den expressiven Typ, oder Geschlecht und Händigkeit der Versuchspersonen, jedoch bestanden Wechselwirkungen.
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The importance of dentofacial attractiveness to the psychosocial well-being of an individual has been well established. Very little information is available regarding dental patient perceptions of a pleasing esthetic image. The purpose of this study was to identify factors distinctive to attractive smiles versus unattractive smiles, as perceived by patients. Standardized format photographs (5 x 7 in, matte finish, at f-32 and 1:2 magnification) of eight male and eight female smiles, framing only lips and teeth, were viewed by 297 subjects. The smiles exhibited differences in symmetry, tooth shade, number of teeth displayed, and height of maxillary lip line, and included both restored and unrestored teeth. Respondents ranked the photographs in order from most to least appealing appearance. Respondents viewed each series of photographs in a similar lighting and time period. A questionnaire identified the respondent's age, sex, race, education, income, and home town. Twenty-five demographic groups were established from the information in the questionnaire. Data were analyzed using stepwise discriminant analysis to determine the combination of smile characteristics that best predicted the ranking. The same female smile was chosen as the most attractive by 24 of the 25 demographic groups. This smile is characterized by natural teeth having light shade, high lip line, a large display of teeth, and radiating symmetry. Two female smiles typified by darker shade and asymmetry were rated by all groups as being least attractive. Two male smiles were judged equal as the most pleasing esthetically. Respondents favored those smiles characterized by light shade, a moderate display of teeth, moderate lip line, and a symmetrical arrangement of teeth. One male smile characterized by darker shade was rated as least attractive. In all cases, tooth shade was the most important factor, followed in sequence by unrestored natural teeth and number of teeth displayed. No correlation was found to exist between specific demographic groups and smile variables.
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The development of functional brain asymmetry during childhood is confirmed by changes in cerebral blood flow measured at rest using dynamic single photon emission computed tomography. Between 1 and 3 years of age, the blood flow shows a right hemispheric predominance, mainly due to the activity in the posterior associative area. Asymmetry shifts to the left after 3 years. The subsequent time course of changes appear to follow the emergence of functions localized initially on the right, but later on the left hemisphere (i.e. visuospatial and later language abilities). These findings support the hypothesis that, in man, the right hemisphere develops its functions earlier than the left.
Article
This review focuses on facial asymmetries during emotional expression. Facial asymmetry is defined as the expression intensity or muscular involvement on one side of the face ("hemiface") relative to the other side and has been used as a behavioral index of hemispheric specialization for facial emotional expression. This paper presents a history of the neuropsychological study of facial asymmetry, originating with Darwin. Both quantitative and qualitative aspects of asymmetry are addressed. Next, neuroanatomical bases for facial expression are elucidated, separately for posed/voluntary and spontaneous/involuntary elicitation conditions. This is followed by a comprehensive review of 49 experiments of facial asymmetry in the adult literature, oriented around emotional valence (pleasantness/unpleasantness), elicitation condition, facial part, social display rules, and demographic factors. Results of this review indicate that the left hemiface is more involved than the right hemiface in the expression of facial emotion. From a neuropsychological perspective, these findings implicate the right cerebral hemisphere as dominant for the facial expression of emotion. In spite of the compelling evidence for right-hemispheric specialization, some data point to the possibility of differential hemispheric involvement as a function of emotional valence.
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Head turning after release from the midline and the Moro response to a full-body drop in 15 full-term newborns lying supine on a custom-built platform was studied. While the lateral bias for head turning was not as pronounced as for the Moro response, it was still assumed in the ratio of 2 (right):1 (left) as predicted by Previc (1991). Onset latency and time-to-peak acceleration were both significantly shorter in the right arm during the initial phase of the Moro response. For both measures, this right arm bias persisted over four consecutive elicitations in most infants. Vaginally delivered infants and those born by Caesarean section did not differ in terms of head preference and the two measures of arm advantage. Our main finding was that infants with a right-sided head preference had a consistently shorter onset latency for the right arm. We interpret this association as stemming from a common labyrinthine asymmetry that involves different vestibulospinal pathways for the neck and arm muscles. In general, our findings are discussed in the context of Previc's (1991) left-otolithic dominance hypothesis and Grattan, De Vos, Levy, and McClintock's (1992) model of newborn functional asymmetries.
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It has been three decades since John Bowlby first presented an over-arching model of early human development in his groundbreaking volume, Attachment. In the present paper I refer back to Bowlby's original charting of the attachment landscape in order to suggest that current research and clinical models need to return to the integration of the psychological and biological underpinnings of the theory. Towards that end, recent contributions from neuroscience are offered to support Bowlby's assertions that attachment is instinctive behavior with a biological function, that emotional processes lie at the foundation of a model of instinctive behavior, and that a biological control system in the brain regulates affectively driven instinctive behavior. This control system can now be identified as the orbitofrontal system and its cortical and subcortical connections. This 'senior executive of the emotional brain' acts as a regulatory system, and is expanded in the right hemisphere, which is dominant in human infancy and centrally involved in inhibitory control. Attachment theory is essentially a regulatory theory, and attachment can be defined as the interactive regulation of biological synchronicity between organisms. This model suggests that future directions of attachment research should focus upon the early-forming psychoneurobiological mechanisms that mediate both adaptive and maladaptive regulatory processes. Such studies will have direct applications to the creation of more effective preventive and treatment methodologies.
Article
In the past 15 years, there have been a number of studies conducted on asymmetries in the perception and production of facial expressions in human and non-human primates as a means of inferring hemispheric specialization for emotions. We review these studies to assess continuity and discontinuity between species in these emotional processes. We further present new data on asymmetries in the production of facial expressions in a sample of captive chimpanzees. Objective measures (hemimouth length and area) and subjective measures (human judgement's of chimeric stimuli) indicate that chimpanzees' facial expressions are asymmetric, with a greater involvement of the left side of the face (right hemisphere) in the production of emotional responses. Left hemimouth was bigger than the right in the facial expressions of pant-hooting, play, and silent bared-teeth (p < 0.05) and it extended laterally more than the right in the categories of pant-hooting, silent bared-teeth, and scream face (p < 0.05). Human judges also reported that the left side of the faces was emotionally more intense in the case of the play and silent bared-teeth categories (p < 0.01). Thus, chimpanzees, like humans and some other non-human primates, show a right hemisphere specialization for facial expression of emotions, which suggests that this functional asymmetry is homologous in all these species.
Lateral asymmetry in intensity of emotional expression
  • Sackeim
Lateral biases in head turning and the Moro response in the human newborn: Are they both vestibular in origin?
  • Ronnqvist