Concealing of facial expressions by a wild Barbary macaque (Macaca sylvanus)

Behavioural research on non-vocal communication among non-human primates and its possible links to the origin of human language is a long-standing research topic. Because human language is under voluntary control, it is of interest whether this is also true for any communicative signals of other species. It has been argued that the behaviour of hiding a facial expression with one’s hand supports the idea that gestures might be under more voluntary control than facial expressions among non-human primates, and it has also been interpreted as a sign of intentionality. So far, the behaviour has only been reported twice, for single gorilla and chimpanzee individuals, both in captivity. Here, we report the first observation of concealing of facial expressions by a monkey, a Barbary macaque (Macaca sylvanus), living in the wild. On eight separate occasions between 2009 and 2011 an adult male was filmed concealing two different facial expressions associated with play and aggression (“play face” and “scream face”), 22 times in total. The videos were analysed in detail, including gaze direction, hand usage, duration, and individuals present. This male was the only individual in his group to manifest this behaviour, which always occurred in the presence of a dominant male. Several possible interpretations of the function of the behaviour are discussed. The observations in this study indicate that the gestural communication and cognitive abilities of monkeys warrant more research attention.     

Facial Expression Wrinkles and Their Relaxation by a Synthetic Peptide

International Journal of Peptide Research and Therapeutics - Expression wrinkles form over time due to repeated facial movements such as smiling and frowning. They have an imprint on facial skin in...     

Forms and Social Signal Value of Smiles Associated with Pleasant and Unpleasant Sensory Experience

Episodes of facial displays involving the zygomatic action (AU12: lip corner pulling or smiling) were selected from a large sample of children (n = 95) exposed to pleasant and unpleasant odours in the presence of an unfamiliar person in order to investigate potential differences in morphological, temporal patterning and social signal value of smiling. In a first experiment, using the facial action coding system (FACS: Ekman & Friesen 1978), a considerable morphological flexibility of smiles was observed in relation to the subjects' hedonic experience. The facial configurations of smiling were formed by a number of actions in the upper (AU 4: brow lowering), middle (AU 9: nose wrinkling) and lower face (AU 14: dimpling, AU 15: lip comer depressing, AU 17: chin raising, AU 23: lip tightening) and the mouth was more often ‘closed’ in response to unpleasant odours. When exposed to pleasant odours, zygomatic action co-occurred more frequently with an opening of the mouth (AUs 25, 26, 27) or with a raising of the cheeks (AU 6). An analysis of the temporal patterning of zygomatic actions showed that they occurred more rapidly, dropped off the face less abruptly with a stepped decrease, were less smooth, and were often associated with shorter gazes directed toward the examiner in response only to unpleasant odours. These findings suggested that a number of subjects might exert some control on their smiling while confronted with a presumed social constraint, namely the smelling of unpleasant odours in the presence of an unfamiliar person. In a second experiment, the communicative value of smiling was investigated in a real-time projection of 10 variants of smiling to a panel of receivers (n = 52). The Duchenne smile (AU 6 + 12 + 25) and smile with lips opening (12 + 25) provided more accurate information about the hedonic valence of the inhaled odour than did the other types of smiling. In contrast, the perceived valence of the facial displays simultaneously combining zygomatic action with muscular actions of the lower face (AUs 15, 17, 23) appeared more difficult to discriminate by untrained receivers. It was hypothesized that the senders displayed some forms of smiling possibly to mask their responsiveness to unpleasant odours in signalling ambiguous or incorrect information about their internal state to a recipient.     

Darwin’s Duchenne: Eye Constriction during Infant Joy and Distress

Darwin proposed that smiles with eye constriction (Duchenne smiles) index strong positive emotion in infants, while cry-faces with eye constriction index strong negative emotion. Research has supported Darwin’s proposal with respect to smiling, but there has been little parallel research on cry-faces (open-mouth expressions with lateral lip stretching). To investigate the possibility that eye constriction indexes the affective intensity of positive and negative emotions, we first conducted the Face-to-Face/Still-Face (FFSF) procedure at 6 months. In the FFSF, three minutes of naturalistic infant-parent play interaction (which elicits more smiles than cry-faces) are followed by two minutes in which the parent holds an unresponsive still-face (which elicits more cry-faces than smiles). Consistent with Darwin’s proposal, eye constriction was associated with stronger smiling and with stronger cry-faces. In addition, the proportion of smiles with eye constriction was higher during the positive-emotion eliciting play episode than during the still-face. In parallel, the proportion of cry-faces with eye constriction was higher during the negative-emotion eliciting still-face than during play. These results are consonant with the hypothesis that eye constriction indexes the affective intensity of both positive and negative facial configurations. A preponderance of eye constriction during cry-faces was observed in a second elicitor of intense negative emotion, vaccination injections, at both 6 and 12 months of age. The results support the existence of a Duchenne distress expression that parallels the more well-known Duchenne smile. This suggests that eye constriction–the Duchenne marker–has a systematic association with early facial expressions of intense negative and positive emotion.     

Do American Crows Pay Attention to Human Gaze and Facial Expressions?

Interactions between species can lead to the evolution of interspecific communication. Non‐verbal communication by humans, both intentional and unintentional, can be interpreted by other species. We tested whether American crows (Corvus brachyrhynchos) were sensitive to human facial features under field conditions by comparing flight initiation distances and urgency of escape behavior to human approaches varying in eye contact and facial expression. We first examined whether crows distinguish between an approaching human who is directly gazing at them and a human approaching them with an averted gaze. In a second experiment, we tested whether crows differentiate a smiling from scowling human approaching them with direct or averted gaze. In the first experiment, we found that crows fled sooner and more urgently when humans were directly gazing at them. Similarly, in the second experiment, crows responded sooner to a direct vs. averted gaze; however, they did not react differently to varying human facial expressions. We suggest that crows use human gaze as a reliable visual cue compared with facial expressions when making decisions about responding to approaching humans. This is the first study to show that a wild corvid species changes its behavior based on human gaze, possibly representing an adaptation to living in human‐dominated urban areas and suggesting crows might perceive human intention by this visual cue.     

Facial Mimicry and Emotion Consistency: Influences of Memory and Context

This study investigates whether mimicry of facial emotions is a stable response or can instead be modulated and influenced by memory of the context in which the emotion was initially observed, and therefore the meaning of the expression. The study manipulated emotion consistency implicitly, where a face expressing smiles or frowns was irrelevant and to be ignored while participants categorised target scenes. Some face identities always expressed emotions consistent with the scene (e.g., smiling with a positive scene), whilst others were always inconsistent (e.g., frowning with a positive scene). During this implicit learning of face identity and emotion consistency there was evidence for encoding of face-scene emotion consistency, with slower RTs, a reduction in trust, and inhibited facial EMG for faces expressing incompatible emotions. However, in a later task where the faces were subsequently viewed expressing emotions with no additional context, there was no evidence for retrieval of prior emotion consistency, as mimicry of emotion was similar for consistent and inconsistent individuals. We conclude that facial mimicry can be influenced by current emotion context, but there is little evidence of learning, as subsequent mimicry of emotionally consistent and inconsistent faces is similar.     

Socioecological correlates of facial mobility in nonhuman anthropoids

Facial mobility, or the variety of facial movements a species can produce, is likely influenced by selection for facial expression in diurnal anthropoids. The purpose of this study is to examine socioecological correlates of facial mobility independent of body size, focusing on social group size and arboreality as possible evolutionary agents. Group size was chosen because facial expressions are important for group cohesion, while arboreality may limit the utility of facial expressions. Data for 12 nonhuman anthropoid species were taken from previous studies and analyzed using a phylogenetic generalized least‐squares approach. Regression results indicate that group size is a good predictor of facial mobility independent of body size. No statistical support was found for the hypothesis that arboreality constrains the evolution of facial mobility. The correlation between facial mobility and group size may be a consequence of selection for more effective facial expression to help manage conflicts and facilitate bonding in larger groups. These findings support the hypothesis that the ultimate function of facial expression is related to group cohesion. Am J Phys Anthropol 2009. © 2009 Wiley‐Liss, Inc.     

Keep Your Opponents Close: Social Context Affects EEG and fEMG Linkage in a Turn-Based Computer Game

In daily life, we often copy the gestures and expressions of those we communicate with, but recent evidence shows that such mimicry has a physiological counterpart: interaction elicits linkage, which is a concordance between the biological signals of those involved. To find out how the type of social interaction affects linkage, pairs of participants played a turn-based computer game in which the level of competition was systematically varied between cooperation and competition. Linkage in the beta and gamma frequency bands was observed in the EEG, especially when the participants played directly against each other. Emotional expression, measured using facial EMG, reflected this pattern, with the most competitive condition showing enhanced linkage over the facial muscle-regions involved in smiling. These effects were found to be related to self-reported social presence: linkage in positive emotional expression was associated with self-reported shared negative feelings. The observed effects confirmed the hypothesis that the social context affected the degree to which participants had similar reactions to their environment and consequently showed similar patterns of brain activity. We discuss the functional resemblance between linkage, as an indicator of a shared physiology and affect, and the well-known mirror neuron system, and how they relate to social functions like empathy.     

The first smile: spontaneous smiles in newborn Japanese macaques (<Emphasis Type="Italic">Macaca fuscata</Emphasis>)

Spontaneous smiles are facial movements that are characterized by lip corner raises that occur during irregular sleep or drowsiness without known external or internal causes. They are shown by human infants and infant chimpanzees. These smiles are considered to be the developmental origin of smiling and laughter. There are some case studies showing that spontaneous smiles occur in Japanese macaques. The goals of this study were to investigate whether newborn Japanese macaques show a considerable number of spontaneous smiles thus to examine the mechanism of them. Seven newborn Japanese macaques were observed in a room for an average of 44 min, and incidental sleeping situations were monitored twice. All seven participants showed spontaneous smiles at least once during the observation. They showed 8.29 spontaneous smiles in average (SD = 10.89; 58 smiles in total), all found in the state of REM sleep. Thirty-nine of the 58 smiles were produced on the left side of the mouth. These characteristics were similar to those of spontaneous smiles in human infants. This is the first evidence that macaques as well as hominoids show a considerable number of spontaneous smiles. These phenomena may facilitate the development of the zygomaticus major muscle, which is implicated in smiling-like facial expressions.     

Dogs Evaluate Threatening Facial Expressions by Their Biological Validity – Evidence from Gazing Patterns

Appropriate response to companions’ emotional signals is important for all social creatures. The emotional expressions of humans and non-human animals have analogies in their form and function, suggesting shared evolutionary roots, but very little is known about how animals other than primates view and process facial expressions. In primates, threat-related facial expressions evoke exceptional viewing patterns compared with neutral or positive stimuli. Here, we explore if domestic dogs (Canis familiaris) have such an attentional bias toward threatening social stimuli and whether observed emotional expressions affect dogs’ gaze fixation distribution among the facial features (eyes, midface and mouth). We recorded the voluntary eye gaze of 31 domestic dogs during viewing of facial photographs of humans and dogs with three emotional expressions (threatening, pleasant and neutral). We found that dogs’ gaze fixations spread systematically among facial features. The distribution of fixations was altered by the seen expression, but eyes were the most probable targets of the first fixations and gathered longer looking durations than mouth regardless of the viewed expression. The examination of the inner facial features as a whole revealed more pronounced scanning differences among expressions. This suggests that dogs do not base their perception of facial expressions on the viewing of single structures, but the interpretation of the composition formed by eyes, midface and mouth. Dogs evaluated social threat rapidly and this evaluation led to attentional bias, which was dependent on the depicted species: threatening conspecifics’ faces evoked heightened attention but threatening human faces instead an avoidance response. We propose that threatening signals carrying differential biological validity are processed via distinctive neurocognitive pathways. Both of these mechanisms may have an adaptive significance for domestic dogs. The findings provide a novel perspective on understanding the processing of emotional expressions and sensitivity to social threat in non-primates.     

Rapid facial mimicry in orangutan play

Emotional contagion enables individuals to experience emotions of others. This important empathic phenomenon is closely linked to facial mimicry, where facial displays evoke the same facial expressions in social partners. In humans, facial mimicry can be voluntary or involuntary, whereby its latter mode can be processed as rapid as within or at 1s. Thus far, studies have not provided evidence of rapid involuntary facial mimicry in animals.This study assessed whether rapid involuntary facial mimicry is present in orangutans (Pongo pygmaeus; N=25) for their open-mouth faces (OMFs) during everyday dyadic play. Results clearly indicated that orangutans rapidly mimicked OMFs of their playmates within or at 1s. Our study revealed the first evidence on rapid involuntary facial mimicry in non-human mammals. This finding suggests that fundamental building blocks of positive emotional contagion and empathy that link to rapid involuntary facial mimicry in humans have homologues in non-human primates.     

Anatomic variations of the nasolabial fold.

The nasolabial fold varies considerably from person to person. Three main groups may be distinguished: convex, concave, and straight. It is the muscles of smiling that are directly responsible for the shape and depth of the fold, and in their absence of function, as in facial palsy, the nasolabial fold disappears. Cadavers were selected in accordance with the nasolabial fold they presented and were dissected to analyze the difference in underlying anatomy between one fold shape in one cadaver and another fold shape in another. The study demonstrates that the nasolabial fold is the result of a conflict between soft and dynamic tissues of the middle face or an interaction between the skin and fat envelope on one side and the underlying muscles on the other. The greater this conflict, the more excess there is of cheek skin and the more pronounced a nasolabial fold. The mechanism that creates the nasolabial fold and the anatomy of the fold are described in this paper.     

Positive Feeling,Negative Meaning: Visualizing the Mental Representations of In-Group and Out-Group Smiles

Even though smiles are seen as universal facial expressions, research shows that there exist various kinds of smiles (i.e., affiliative smiles, dominant smiles). Accordingly, we suggest that there also exist various mental representations of smiles. Which representation is employed in cognition may depend on social factors, such as the smiling person’s group membership: Since in-group members are typically seen as more benevolent than out-group members, in-group smiles should be associated with more benevolent social meaning than those conveyed by out-group members. We visualized in-group and out-group smiles with reverse correlation image classification. These visualizations indicated that mental representations of in-group smiles indeed express more benevolent social meaning than those of out-group smiles. The affective meaning of these visualized smiles was not influenced by group membership. Importantly, the effect occurred even though participants were not instructed to attend to the nature of the smile, pointing to an automatic association between group membership and intention.     

Face Gender Influences the Looking Preference for Smiling Expressions in 3.5-Month-Old Human Infants

Young infants are typically thought to prefer looking at smiling expressions. Although some accounts suggest that the preference is automatic and universal, we hypothesized that it is not rigid and may be influenced by other face dimensions, most notably the face’s gender. Infants are sensitive to the gender of faces; for example, 3-month-olds raised by female caregivers typically prefer female over male faces. We presented neutral versus smiling pairs of faces from the same female or male individuals to 3.5-month-old infants (n = 25), controlling for low-level cues. Infants looked longer to the smiling face when faces were female but longer to the neutral face when faces were male, i.e., there was an effect of face gender on the looking preference for smiling. The results indicate that a preference for smiling in 3.5-month-olds is limited to female faces, possibly reflective of differential experience with male and female faces.     

A selective emotional decision-making bias elicited by facial expressions

Emotional and social information can sway otherwise rational decisions. For example, when participants decide between two faces that are probabilistically rewarded, they make biased choices that favor smiling relative to angry faces. This bias may arise because facial expressions evoke positive and negative emotional responses, which in turn may motivate social approach and avoidance. We tested a wide range of pictures that evoke emotions or convey social information, including animals, words, foods, a variety of scenes, and faces differing in trustworthiness or attractiveness, but we found only facial expressions biased decisions. Our results extend brain imaging and pharmacological findings, which suggest that a brain mechanism supporting social interaction may be involved. Facial expressions appear to exert special influence over this social interaction mechanism, one capable of biasing otherwise rational choices. These results illustrate that only specific types of emotional experiences can best sway our choices.     

Understanding the recognition of facial identity and facial expression

Faces convey a wealth of social signals. A dominant view in face-perception research has been that the recognition of facial identity and facial expression involves separable visual pathways at the functional and neural levels, and data from experimental, neuropsychological, functional imaging and cell-recording studies are commonly interpreted within this framework. However, the existing evidence supports this model less strongly than is often assumed. Alongside this two-pathway framework, other possible models of facial identity and expression recognition, including one that has emerged from principal component analysis techniques, should be considered.     

Dynamically engaged smiling predicts cooperation above and beyond average smiling levels

Smiling has been conceptualized as a signal of cooperative intent, yet smiles are easy to fake. We suggest that contextually appropriate, dynamically engaged smiling imposes an attentional cost, thereby making engaged smiling a plausible “honest signal” of cooperative intent. To test this hypothesis, we analyzed data from 123 pairs of same-sex strangers having “getting-to-know-you” conversations who subsequently played a one-shot prisoner's dilemma together. We calculated the strength of engagement in smiling using a cross-lagged auto-regressive model for dyadic data. We found that when an individual's partner (the signaler) tended to smile in a more responsive way, that individual (the receiver) was more likely to cooperate. Conversely, when a signaler tended to smile in a less responsive way, the receiver was less likely to cooperate. These effects were present over-and-above the effects of average levels of smiling and self-reported liking, which also predicted likelihood of cooperation. However, dynamically engaged smiling did not predict cooperation on the part of the signaler, suggesting that receivers weight the importance of engagement more highly than they should, or even that engaged smiling might be a manipulative display. These results illustrate how conversational dynamics can influence evolutionary signaling.     

Dynamics of the gamma-responses in an 8-second interval between facial and trigger stimuli as dependent the success of task performance

A cognitive set to facial expression was used as a model with the loading on working memory being increased by increasing the interval between the facial and triggering stimuli to 8 seconds. The aim was to determine whether the intensity of brain potentials evoked in a range of 41–60 Hz (the range 15–60 Hz was used) by facial stimuli is associated with the “success” of task performance (mistake rate). An index of average amplitudes of EEG oscillations was used to measure the response to facial stimuli, and γ responses proved to be associated with the number of mistakes in performing the task. The results make it possible to consider the γ responses to facial stimuli as an EEG correlate of the internal states that correspond to adequate actions of the subject in the test with a 8-s interval between the facial and trigger stimuli.