The big warm smile of cheaters: lateral posing biases and emotional expressions in displaying facial trustworthiness

ABSTRACT

Cheater detection, which is a prerequisite for the evolution of social cooperation, has been successfully simulated in laboratory settings. However, the process has not been perfect because the detection rate has usually been just above chance. The present study investigated the role of lateral posing biases and emotional expressions in displaying trustworthiness, which plays a crucial role in cheater detection. Participants (N?=?30 and 28 in Experiments 1 and 2, respectively) observed facial photographs of cheaters and cooperators in an economic game and evaluated their facial expressions in terms of emotional valence and arousal. The models in the photographs had turned their left or right cheek to the camera to display their trustworthiness in the economic game. The results indicated that cheaters showing their left cheek were rated as more emotionally positive than cheaters showing their right cheek. This lateral difference was not observed for cooperators. A left cheek advantage in emotional arousal was found for both cheaters and cooperators. These results suggest that cheaters use a fake smile on the emotional side of their face (i.e., the left) to conceal their uncooperative attitude.     

Is trustworthiness lateralized in the face? Evidence from a trust game

A turn of the head can be used to convey or conceal emotion, as the left side of the face is more expressive than the right. As the left cheek moves more when smiling, the present study investigated whether perceived trustworthiness is lateralized to the left cheek, using a trust game paradigm. In Experiment 1, participants were asked to share money with male and female “virtual partners.” Left–left or right–right composite faces were used to represent the partners. There were no differences in the amount shared based on composite face, suggesting trustworthiness is not lateralized in the face. However, there was a robust effect whereby female partners were perceived to be significantly more trustworthy than males. In Experiment 2, the virtual partners presented either the left or the right cheek prominently. As in Experiment 1, the amount shared with the partners did not change depending on the cheek presented. Interestingly, female partners were again sent significantly more money than males. We found no support for lateralized trustworthiness in the face, suggesting that asymmetries in the face are not large enough to influence trustworthiness judgements. Instead, more stable facial features, such as sex-typical characteristics, appear to influence perceived trustworthiness.     

Digitizing the moving face during dynamic displays of emotion

Humans typically decode facial signals during dynamic interactions in which the face moves. In this study, we digitized real time video signals in order to examine movement asymmetries across the face during emotional and nonemotional expressions. Forty dextral males were tested. For each expression, a 400 ms video segment was analyzed for changes in signal value (pixel intensity) over consecutive frames. The upper and lower face regions were examined separately due to differences in the cortical enervation of facial muscles in the upper (bilateral) vs lower face (contralateral). Results revealed distinctly different movement asymmetries over the lower and upper hemiface. In the upper face, more movement occurred over the right side for most facial expressions, regardless of emotionality. The latter finding questions the assumption that muscles of the upper face are symmetrical and/or bilaterally enervated in a symmetrical manner. In the lower face, negative expressions linked to fight-flight emotions (i.e. fear, anger) were associated with greater left sided movement, whereas happiness tended to be associated with more right sided movement. No consistent pattern of movement asymmetry occurred for nonemotional expressions. Although the valence-related movement asymmetries in the lower face are consistent with neuropsychological models of emotional expressivity, it remains unclear whether they reflect activation or inhibitory hemispheric mechanisms. Taken together, these data suggest that multiple factors may contribute to expressive movement asymmetries of the face.     

The Development of Facedness

Thirty-two children of both sexes, ranging in age from 6 to 13 years, were photographed while posing or imitating happiness, sadness or surprise. Full-face photographs which were considered by independent judges to express the intended emotions were submitted to a split-face recombination procedure that created two composites from each face, one from the left side and the other from the right. Independent observers found the left composites to be more expressive than the right m the older group (age 12–13), but not in the younger groups, who evinced no left-right asymmetries. This finding applied similarly to the three emotions, and did not depend on an age-related change in the capacity for emotional expression.Further, left-right asymmetries in facial expression, where present, did not correlate with difference in size between the two halves of the face, and were found for both the upper and lower parts of the face. It is concluded that the advantage of the left hemiface for emotional expression, which is typical of adults, is the result of growth and development. While this facial asymmetry is likely to depend on an hemispheric asymmetry favoring the right side of the brain for the volitional control of the facial musculature, the neural mechanisms of the phenomenon of facedness are still largely obscure.     

Celebrity chefs put their left cheek forward: Cover image orientation in celebrity cookbooks

Portrait pose orientations influence perception: the left cheek is more emotionally expressive; females’ right cheeks appear more attractive. Posing biases are established in paintings, photographs, and advertisements, however, book covers have not previously been examined. This paper assesses cover image orientation in a book genre that frequently features a cover portrait: the celebrity cookbook. If marketers intuitively choose to enhance chefs’ emotional expressivity, left cheek poses should predominate; if attractiveness is more important, right cheek poses will be more frequent for females, with a left or no cheek bias for males. Celebrity cookbook covers (N?=?493) were sourced online; identity, portrait orientation, photo type, and sex were coded. For celebrity cookbooks, left cheek covers (39.6%) were more frequent than right cheek (31.6%) or midline covers (28.8%); sex did not predict pose orientation. An interaction between photo type and sex bordered on significance: photo type did not influence females’ pose orientation; for males, the left cheek bias present for head and torso images was absent for full body and head only photos. Overall, the left cheek bias for celebrity cookbook covers implies that marketers intuitively select images that make the chefs appear happier and/or more emotionally expressive, enhancing engagement with the audience.     

Examining the effects of inversion on lateralisation for processing facial emotion

There is an increasing amount of evidence which suggests that each hemisphere is differently specialised for processing facial stimuli, with the right hemisphere specialised for the processing of configural information and the left hemisphere specialised for the processing of featural information. While there is evidence for this distinction from studies of face recognition, it has not been shown in studies of lateralisation for processing facial emotion. In this study the chimeric faces test was used with faces expressing anger, disgust, fear, happiness, sadness or surprise, presented in either an upright or an inverted orientation. When presented upright, a significant right hemisphere bias was found for all six emotions. However, when inverted, a significant left hemisphere bias was found for the processing of happiness and surprise, but not for the processing of negative emotions (although the analysis was approaching significance for anger). These findings support the hypothesis that each hemisphere is differently specialised for processing facial emotion, but contradicts previous work that examined the effects of inversion on chimeric face stimuli.     

Composition in portraits: Selfies and wefies reveal similar biases in untrained modern youths and ancient masters*

Previous analyses suggest that artists prefer poses showing the left side of the subject’s face when composing a portrait, but showing the right side when composing their own self-portrait. There is also some evidence that artists may prefer compositions with key features on the right of the picture. Do these findings generalize to spontaneous, pseudo-artistic productions by individuals with no formal training in painting and art history? To investigate this issue, we tested a sample of 104 British schoolchildren and teenagers (mean age?=?13.8 years; 80 females). We analysed posing biases in individual photographic self-portraits (“selfies”) as well as of self-portraits including also the portrait of a friend (“wefies”). Our results document a bias for showing the left cheek in selfies, a bias for placing the selfie-taker on the right in wefies, and a bias for showing two left cheeks over two right cheeks, again in wefies. These biases are reminiscent of what has been reported for selfies in adult non-artists and for portraits and self-portraits by artists in the 16th–18th centuries. Thus, these results provide new evidence in support of a biological basis for side biases in portraits and self-portraits independently of training and expertise.     

Perceptual asymmetries in a time estimation task with emotional sounds

Four experiments investigated potential interactions between emotional content and perceptual asymmetries in the estimation of short time intervals. In all experiments, the word “bower” was presented monaurally to the left or right ear in an emotional tone and participants performed a temporal bisection task. In Experiment 1, angry and neutral stimuli ranged in duration from 260 to 440 ms (in steps of 20 ms) whereas in Experiments 2–4, durations ranged from 260 to 480 ms (in steps of 20 ms). In Experiment 3, the emotional tone of happiness replaced anger. In Experiment 4, anger and happiness were used as stimuli. In all experiments, results showed a larger bisection point for the right compared to the left ear. In addition, in all experiments, the constant error was farther away from zero for the right than for the left ear. The bisection point was also longer for the angry (Experiments 1 and 2) or happy (Experiment 3) than for the neutral emotional tone. Finally, happiness produced a shorter bisection point than anger in Experiment 4. Results are discussed in terms of their implications for time perception mechanisms and their potential cerebral representation.     

Faces of glory: the left-cheek posing bias for medallists of Brazilian jiu-jitsu competitions

Laboratory studies have shown that people tend to show the left side of their face when asked to broadly express emotions, while they tend to show the right side when asked to hide emotions. Because emotions are expressed more intensely in the left side of the face, it is hypothesized that an individual’s intention to express or hide emotions biases the direction of lateral facial poses. The present study tested this hypothesis using photographic portraits of individuals experiencing emotional events in a naturalistic setting: the reception of medals in Brazilian jiu-jitsu competitions. Portrait photographs of Brazilian jiu-jitsu competitors were sourced online (N?=?460) and were rated by two independent raters in terms of posing direction, emotional expression, and medal colour. Gold and silver medallists showed their left cheeks to the camera for commemorative photographs taken immediately after the medal ceremony. Positive emotions were expressed more often for gold medallists than silver ones. The left-cheek posing bias observed in the present study supports the hypothesis that the intended purpose of expressing or hiding emotions determines the direction of lateral posing biases, and extends the laboratory findings to situations in the real world.     

The effect of left and right poses on the expression of facial emotion

Research, using composite facial photographs has demonstrated that left-left composites are more emotionally expressive than are right-right composites. The present study investigated whether hemifacial asymmetries in expression are apparent in photographs, that feature one side of the face more than the other. Photographs were taken of the models who turned their heads: (a) 15 degrees to the left, (b) 15 degrees to the right or (c) faced directly towards the camera. It was predicted that left hemiface and midline photographs would be judged as more emotionally expressive than right hemiface photographs, where the left hemiface is less prominent. Three hundred and eighty-four participants viewed photographs of the three posing conditions, and rated each photograph along an emotional expressivity scale. Midline and left hemiface portraits were rated as more emotionally expressive than were right hemiface portraits. To investigate whether this effect was caused by observer's aesthetic/perceptual biases, mirror-reversed versions of the three posing conditions were included. Left hemiface and midline portraits were rated as more emotionally expressive, irrespective of whether they were mirror-reversed. It was concluded that head turns of just 15 degrees can bring about significant changes in the perceived emotionality. The relevance of these findings to painted portraits, which feature the left hemiface more than the right, is discussed.     

Right brain damage impairs recognition of negative emotions

Patients with right or left hemisphere-damage and normal control groups were asked to judge facial emotions from photographs presented in two orientations--upright, inverted. Responses were elicited with a matching and a verbal labelling task. Normal controls were significantly superior in the judgment of facial emotions than left hemisphere-damaged patients, who in turn were significantly superior than right hemisphere-damaged patients. Negative-aroused (fear, anger) and negative-nonaroused (sadness, disgust) facial expressions were recognized with significantly greater accuracy by left hemisphere-damaged patients compared to right hemisphere-damaged patients; the group difference in performance was nonsignificant for positive (happiness, surprise) emotions.     

Recognition of emotion in hemifaces presented to the left and right visual fields

Thirty-two right-handed subjects (16 males and 16 females) participated in a choice reaction time experiment replicating two previous studies which demonstrated the superiority of the left hemisphere in rapidly identifying facial emotion as either positive or negative. Slides of hemifaces split along the vertical axis, showing either positive (happiness, surprise) or negative (anger, disgust, or sadness) affect were presented tachistoscopically to either the left or right visual field. A 2 X 2 X 2 mixed ANOVA revealed main effects for visual field and type of affect. In contrast to earlier studies which presented full face stimuli, presentation of hemifaces produced a strong left visual field advantage and, as expected, positive faces produced faster reaction times than negative faces.     

Left cheek bias for emotion perception,but not expression,is established in children aged 3–7 years

As the left hemiface is controlled by the emotion-dominant right hemisphere, emotion is expressed asymmetrically. Portraits showing a model's left cheek consequently appear more emotive. Though the left cheek bias is well established in adults, it has not been investigated in children. To determine whether the left cheek biases for emotion perception and expression are present and/or develop between the ages of 3 and 7 years, 145 children (71 male, 74 female; M age?=?65.49 months) completed two experimental tasks: one assessing biases in emotion perception, and the other assessing biases in emotion expression. Regression analysis confirmed that children aged 3–7 years find left cheek portraits happier than right cheek portraits, and age does not predict the magnitude of the bias. In contrast when asked to pose for a photo expressing happiness children did not show a left cheek bias, with logistic regression confirming that age did not predict posing orientations. These findings indicate that though the left cheek bias for emotion perception is established by age 3, a similar bias for emotion expression is not evident by age 7. This implies that tacit knowledge of the left cheek's greater expressivity is not innate but develops in later childhood/adolescence.     

Brain signatures of perceiving a smile: Time course and source localization

Facial happiness is consistently recognized faster than other expressions of emotion. In this study, to determine when and where in the brain such a recognition advantage develops, EEG activity during an expression categorization task was subjected to temporospatial PCA analysis and LAURA source localizations. Happy, angry, and neutral faces were presented either in whole or bottom‐half format (with the mouth region visible). The comparison of part‐ versus whole‐face conditions served to examine the role of the smile. Two neural signatures underlying the happy face advantage emerged. One peaked around 140 ms (left N140) and was source‐located at the left IT cortex (MTG), with greater activity for happy versus non‐happy faces in both whole and bottom‐half face format. This suggests an enhanced perceptual encoding mechanism for salient smiles. The other peaked around 370 ms (P3b and N3) and was located at the right IT (FG) and dorsal cingulate (CC) cortices, with greater activity specifically for bottom‐half happy versus non‐happy faces. This suggests an enhanced recruitment of face‐specific information to categorize (or reconstruct) facial happiness from diagnostic smiling mouths. Additional differential brain responses revealed a specific “anger effect,” with greater activity for angry versus non‐angry expressions (right N170 and P230; right pSTS and IPL); and a coarse “emotion effect,” with greater activity for happy and angry versus neutral expressions (anterior P2 and posterior N170; vmPFC and right IFG). Hum Brain Mapp 36:4287–4303, 2015. © 2015 Wiley Periodicals, Inc.     

Hemispheric asymmetries in processing emotional expressions

Three experiments are reported on visual field asymmetries in the perception of emotional expressions on the face. In experiment I full faces expressing six different emotions were presented unilaterally for exposure durations, allowing the subject to judge whether the facial expression was positive or negative. Right-handed subjects judged all expressions except happiness as more negative when presented in the left visual field (LVF). This effect was smaller for left-handers and was absent in left-handers who use the non-inverted writing posture. In experiment II subjects were presented with happy, sad and “mixed” chimeric faces, projected to each visual field, for durations allowing only the detection of the existence of a face. LVF presentations produced greater differential rating of emotional valence for the three types of stimuli. In experiment III chimeric faces containing happy and sad expressions were presented unilaterally for durations allowing the subject to perceive the existence of two expressions on the face. The subjects were required to decide whether the mood expressed in the face was predominantly negative or positive. RVF presentations resulted in a bias toward positive judgements. These results indicate right hemispheric superiority for the perception and processing of emotional valence and a left hemispheric perceptual bias toward positive aspects of emotional stimuli.     

Left-handers' smiles: asymmetries in the projection of a posed expression

Asymmetries in the expression of a posed smile and in a relaxed facial expression were observed in 24 left-handers. Neither writing position nor familial sinistrality predicted the variance of the results. Left-handers were found to smile more with their left than right side of face; an asymmetry which had previously been observed in right-handers. If anything, left-handers' smiles were more asymmetric, though in the same direction, than right-handers. When relaxed, however, the left-handers' face was judged more unhappy on its right than left side--a reversal of the direction of asymmetry previously noted in right-handers' relaxed expressions. No single neurological or psychological theory accounts for these results; it is suggested that hand preference may exert a myotonic effect which is reflected in judgements of relaxed facial expressions.     

Asymmetry of facial expression in brain damaged subjects

Chimerical symmetrical faces were constructed from 93 photographs of unilaterally brain damaged patients. Pairs of complementary chimeras were presented to 30 normals who were requested to choose the most expressive face of each pair. Results indicate that the left half of the face is judged as more expressive than the right one (a) if the patient is left-injured and (b) when the expression is not the smile. This asymmetry is thus under the control of a central asymmetrical processor and it seems that positive emotions depend upon a particular central mechanism, as suggested in previous studies.     

Development of hemiface size asymmetry

Facial size asymmetries for the upper and lower face were measured from photographs of 40 neonates (3 days old), 40 preschoolers (2-4 years), and 40 young adults (18-24 years), approximately equally divided by sex. The right hemiface was significantly larger than the left in the three age groups, and there were no differences in the distributions of asymmetry as a function of age.     

Facing up to stereotypes: Surgeons and physicians are no different in their emotional expressiveness

Of all the differences between surgeons and physicians that are discussed in the medical profession and in the community at large, one distinction stands out for its frequency of use: surgeons are less emotional than physicians, particularly in their relationships with patients. Here we tested this stereotype by analysing the portraits that 5914 surgeons and physicians had provided for patients to view when selecting a doctor. There is an asymmetry in the degree to which emotional information is conveyed by the face, with the right side being less expressive than the left. Hence, if the stereotype were true, surgeons would be more likely than physicians to show their right cheek in the photographs. While the results for doctors confirmed previous reports of a difference due to sex in which female doctors were more likely to show the left cheek than male doctors, we found that the doctors' specialization did not predict the way they turned in their portraits. Hence, the notion that surgeons face their patients less emotionally than physicians is not supported by the data.     

Event-related repetitive TMS reveals distinct, critical roles for right OFA and bilateral posterior STS in judging the sex and trustworthiness of faces

Judging the sex of faces relies on cues related to facial morphology and spatial relations between features, whereas judging the trustworthiness of faces relies on both structural and expressive cues that signal affective valence. The right occipital face area (OFA) processes structural cues and has been associated with sex judgments, whereas the posterior STS processes changeable facial cues related to muscle movements and is activated when observers judge trustworthiness. It is commonly supposed that the STS receives inputs from the OFA, yet it is unknown whether these regions have functionally dissociable, critical roles in sex and trustworthiness judgments. We addressed this issue using event-related, fMRI-guided repetitive transcranial magnetic stimulation (rTMS). Twelve healthy volunteers judged the sex of individually presented faces and, in a separate session, whether those same faces were trustworthy or not. Relative to sham stimulation, RTs were significantly longer for sex judgments when rTMS was delivered over the right OFA but not the right or left STS, and for trustworthiness judgments on male but not female faces when rTMS was delivered over the right STS or left STS but not the right OFA. Nonetheless, an analysis of the RT distributions revealed a possible critical role also for the right OFA in trustworthiness judgments, limited to faces with longer RTs, perhaps reflecting the later, ancillary use of structural cues related to the sex of the face. On the whole, our findings provide evidence that evaluations of the trustworthiness and sex of faces rely on functionally dissociable cortical regions.