Incidence of the half-left profile pose in single-subject portraits

The Intricate Web of Asymmetric Processing of Social Stimuli in Humans

Although the population-level preference for the use of the right hand is the clearest example of behavioral lateralization, it represents only the best-known instance of a variety of functional asymmetries observable in humans. What is interesting is that many of such asymmetries emerge during the processing of social stimuli, as often occurs in the case of human bodies, faces and voices. In the present paper, after reviewing previous literature about human functional asymmetries for social and emotional stimuli, we suggest some possible links among them and stress the necessity of a comprehensive account (in both ontogenetic and phylogenetic terms) for these not yet fully explained phenomena. In particular, we propose that the advantages of lateralization for emotion processing should be considered in light of previous suggestions that (i) functional hemispheric specialization enhances cognitive capacity and efficiency, and (ii) the alignment (at the population level) of the direction of behavioral asymmetries emerges, under social pressures, as an evolutionary stable strategy.

Keep a Left Profile, Baby! The Left-Cradling Bias Is Associated with a Preference for Left-Facing Profiles of Human Babies

The left-cradling bias (LCB) refers to the (typically female) preference to hold an infant on the left side of one’s own body. Among the three main accounts proposed for such a phenomenon, namely the “handedness”, “heartbeat” and “hemispheric asymmetry” hypotheses, the latter has met with the greatest empirical success. Accordingly, the LCB would facilitate the communication of socio-emotional information through the right hemisphere of both the cradled and the cradling individual, and should emerge mainly in face-to-face interactions. In this regard, it should be noticed that when the infant’s body is oriented toward the cradler, the left or right side of their face is relatively more visible to left- and right-cradlers, respectively. Therefore, we hypothesized that the LCB might also be associated with a preference for left-facing profiles (i.e., those showing the left, and more expressive, hemiface/cheek) of human babies. In order to test our hypothesis, we assessed the cradling-side preferences of female participants, as well as their preference for the left- or right-facing profile of a human infant depicted in a drawing. Left-cradlers exhibited a significantly larger preference for the left-facing version of the drawing compared with right-cradlers, a finding further corroborating the right-hemisphere hypothesis.

Differences over time in head orientation in European portrait paintings

There is evidence for a tendency for European portrait paintings to have the head oriented so that the left side of the face is visible more than the right side. This is particularly the case for female sitters. There is evidence that the left side of the face shows emotion more than the right side does, so it has been proposed that there is a tendency for artists or sitters to want to show more of the emotionality of the sitter. It is shown here that the left-side tendency varies by date. In two studies, large samples were drawn from European gallery collections (study 1) and the National Portrait Gallery in London (study 2). The studies showed a strong left side tendency before 1600, absence of the tendency in the seventeenth and eighteenth centuries, and some recurrence of it in the nineteenth and twentieth centuries, modulated by changing gender differences. These findings show that cultural, historical, or art-historical factors are likely to be involved in determining tendencies in head orientation as well as psychological ones.

Visual attention during the evaluation of facial attractiveness is influenced by facial angles and smile

OBJECTIVE

To examine the changes in visual attention influenced by facial angles and smile during the evaluation of facial attractiveness.

MATERIALS AND METHODS

Thirty-three young adults were asked to rate the overall facial attractiveness (task 1 and 3) or to select the most attractive face (task 2) by looking at multiple panel stimuli consisting of 0°, 15°, 30°, 45°, 60°, and 90° rotated facial photos with or without a smile for three model face photos and a self-photo (self-face). Eye gaze and fixation time (FT) were monitored by the eye-tracking device during the performance. Participants were asked to fill out a subjective questionnaire asking, "Which face was primarily looked at when evaluating facial attractiveness?"

RESULTS

When rating the overall facial attractiveness (task 1) for model faces, FT was highest for the 0° face and lowest for the 90° face regardless of the smile ( P < .01). However, when the most attractive face was to be selected (task 2), the FT of the 0° face decreased, while it significantly increased for the 45° face ( P < .001). When facial attractiveness was evaluated with the simplified panels combined with facial angles and smile (task 3), the FT of the 0° smiling face was the highest ( P < .01). While most participants reported that they looked mainly at the 0° smiling face when rating facial attractiveness, visual attention was broadly distributed within facial angles.

CONCLUSIONS

Laterally rotated faces and presence of a smile highly influence visual attention during the evaluation of facial esthetics.

What Affects Facing Direction in Human Facial Profile Drawing? A Meta-Analytic Inquiry

Two meta-analyses were conducted to examine two potential sources of spatial orientation biases in human profile drawings by brain-intact individuals. The first examined profile facing direction as function of hand used to draw. The second examined profile facing direction in relation to directional scanning biases related to reading/writing habits. Results of the first meta-analysis, based on 27 study samples with 4171 participants, showed that leftward facing of profiles (from the viewer's perspective) was significantly associated with using the right hand to draw. The reading/writing direction meta-analysis, based on 10 study samples with 1552 participants, suggested a modest relationship between leftward profile facing and primary use of a left-to-right reading/writing direction. These findings suggest that biomechanical and cultural factors jointly influence hand movement preferences and in turn the direction of facing of human profile drawings.

Pupil dilations reflect why rembrandt biased female portraits leftward and males rightward

Portrait painters are experts at examining faces and since emotional content may be expressed differently on each side of the face, consider that Rembrandt biased his male portraits to show their right-cheek more often and female portraits to show their left-cheek more often. This raises questions regarding the emotional significance of such biased positions. I presented rightward and leftward facing male and female portraits. I measured observers’ pupil size while asking observers to report how (dis)pleasing they found each image. This was a methodological improvement over the type of research initially done by Eckhard Hess who claimed that pupils dilate to pleasant images and constrict to unpleasant images. His work was confounded since his images’ luminances and contrasts across conditions were inconsistent potentially affecting pupil size. To overcome this limitation I presented rightward or leftward facing male and female portraits by Rembrandt to observers in either their original or mirror-reversed position. I found that in viewing male portraits pupil diameter was a function of arousal. That is, larger pupil diameter occurred for images rated both low and high in pleasantness. This was not the case with female portraits. I discuss these findings in regard to the perceived dominance of males and how emotional expressions may be driven by hemispheric laterality.

The silent social/emotional signals in left and right cheek poses: a literature review

When posing for a painted or photographic portrait, people are more likely to offer their left, rather than right, cheek (e.g., the Mona Lisa). Why? This paper reviews research investigating the left cheek bias, and the reasons underlying this posing asymmetry. Ruling out mechanical and perceptual biases, the paper focuses on the silent emotional and social signals conveyed by left and right cheek poses, demonstrating that people intuitively offer the left cheek to express emotion and perceive left cheek poses as more emotional. Moreover, because the left cheek appears more emotionally expressive, we unconsciously use cheek shown as a cue when presenting or determining academic specialisation, scientific standing, and even political affiliation. The research is consistent in suggesting that something as subtle as a 15° head turn implicitly influences others' perceptions: if you want to be perceived as open and creative, rather than dry and scientific, it might be time to turn the other cheek.

Lateral organisation in nineteenth-century studio photographs is influenced by the direction of writing: a comparison of Iranian and Spanish photographs

The direction of reading has been found to have a significant effect upon aesthetic preference, with left-to-right readers showing a preference for stimuli with a rightward directionality while right-to-left readers prefer stimuli with a leftward directionality. This study looks at a large set of posed, studio photographs to study the cultural interaction between direction of reading and lateral organisation, comparing a corpus of 735 nineteenth-century photographs from Iran (right-to-left reading) with a similar corpus of 898 photographs from Spain (left-to-right readers). Five separate types of composition were studied: linear ordering, usually by height; couples; individuals posing by a chair; individuals posing by a table; and portraits. Lateral preferences were found for all five types of photograph, with the lateral organisation of Iranian photographs being the reverse of that in the Spanish photographs. These data provide support for the influence of direction of reading upon aesthetic organisation in naturalistically produced photographs.

Asymmetrical facial expressions in portraits and hemispheric laterality: a literature review

Studies of facial asymmetry have revealed that the left and the right sides of the face differ in emotional attributes. This paper reviews many of these distinctions to determine how these asymmetries influence portrait paintings. It does so by relating research involving emotional expression to aesthetic pleasantness in portraits. For example, facial expressions are often asymmetrical-the left side of the face is more emotionally expressive and more often connotes negative emotions than the right side. Interestingly, artists tend to expose more of their poser's left cheek than their right. This is significant, in that artists also portray more females than males with their left cheek exposed. Reasons for these psychological findings lead to explanations for the aesthetic leftward bias in portraiture.

Handedness, Hinduism and sculpture: searching for evidence of lateralisation

The majority of people throughout the world show extreme preference for the right hand. We studied lateral bias depicted in ancient Indian sculptures dating between the 7th and 9th centuries ad. A total of 288 sculptures were selected from various excavation sites/museums and the frequencies were computed on 13 different criteria in order to see the preferential bias for hand depicted in sculptures of male and female figures. The findings are discussed in the light of Hindu mythology and rituals.

Dominance of the left oblique view in activating the cortical network for face recognition

Faces in portraits are often depicted from the left 3/4 view (an oblique view of the face that is intermediate between the frontal view and left profile). Here, we used functional magnetic resonance imaging (fMRI) to show that, compared with photographs of right 3/4 views of familiar faces, photographs of left 3/4 views of the same faces elicited stronger neural responses in the right middle occipital/inferior parietal cortex, and right inferior frontal gyrus; which are known to be involved in face recognition. By contrast, there was no differential activation in the temporal cortex including the superior temporal sulcus and fusiform gyrus, which are thought to process face-related visual stimuli at a stage that precedes recognition. We suggest that the preference for the left 3/4 view of faces was produced at a later stage of facial information processing that involves attention or memory retrieval.

Accelerated recognition of left oblique views of faces

Because faces in portraits are depicted more frequently in a left rather than a right oblique (half-profile or 3/4) view, we addressed the question of whether people find it easier to recognize the left or right 3/4 view of a familiar person's face. We examined the ability of 13 subjects to match familiar faces that were presented in either the left or right 3/4 view, with names that were presented either before or after the faces (face-name and name-face matching tasks, respectively). In both tasks, the subjects responded more rapidly to a left than to a right 3/4 view of the same face. This suggests that during face recognition the processing of information from faces that are presented in the left 3/4 view is dominant over the processing of right 3/4 views of familiar faces.

Hemispheric asymmetries and gender influence Rembrandt's portrait orientations

For centuries painters have predominantly painted portraits with the model's left-cheek facing the viewer. This has been even more prevalent with females ( approximately 68%) than males ( approximately 56%). Numerous portraits painted by Rembrandt typify this unexplained phenomenon. In a preliminary experiment, subjects judged 24 emotional and social character traits in 20 portraits by Rembrandt. A factor analysis revealed that females with their left cheek exposed were judged to be much less socially appealing than less commonly painted right-cheeked females. Conversely, the more commonly painted right-cheeked males were judged to be more socially appealing than either left-cheeked males or females facing either direction. It is hypothesized that hemispheric asymmetries regulating emotional facial displays of approach and avoidance influenced the side of the face Rembrandt's models exposed due to prevailing social norms. A second experiment had different subjects judge a different collection of 20 portraits by Rembrandt and their mirror images. Mirror-reversed images produced the same pattern of results as their original orientation counterparts. Consequently, hemispheric asymmetries that specify the emotional expression on each side of the face are posited to account for the obtained results.

Laterality of expression in portraiture: putting your best cheek forward

Portraits, both photographic and painted, are often produced with more of one side of the face showing than the other. Typically, the left side of the face is overrepresented, with the head turned slightly to the sitter's right. This leftward bias is weaker for painted male portraits and non-existent for portraits of scientists from the Royal Society. What mechanism might account for this bias? Examination of portraits painted by left- and right-handers and of self-portraits suggests that the bias is not determined by a mechanical preference of the artist or by the viewer's aesthetics. The leftward bias seems to be determined by the sitters and their desire to display the left side of their face, which is controlled by the emotive, right cerebral hemisphere. When we asked people to portray as much emotion as possible when posing for a family portrait, they tended to present the left side of their face. When asked to pose as scientists and avoid portraying emotion, participants tended to present their right side. The motivation to portray emotion, or conceal it, might explain why portraits of males show a reduced leftward bias, and also why portraits of scientists from the Royal Society show no leftward bias.

Comparison of perceptions of computer-animated left- and right-facing profiles

PURPOSE

Although scientific publications differ in displaying left- or right-facing profiles, there are few systematic studies of the possible effects of directional biases and laterality on patients' and clinicians' perceptions of treatment need, outcomes, and satisfaction. As part of a research program to quantitate the physical bases of the perceived zone of acceptability and most-pleasing facial profiles, responses to computer-animated left- and right-facing soft-tissue profile images were compared and related to eye and hand preference.

MATERIALS AND METHODS

Standardized left-facing, soft-tissue profile images were captured in color and digitized. The right-facing profile was created by reversing the left profile image to display a mirror image. Using imaging and customized morphing software, retrusive and protrusive extremes were created, from which transitional frames were developed to display five features of the soft-tissue profile: upper lip, chin, bimaxillary position, lower face height, and mandible. One left- and one right-facing profile for a Class II division 1 female, and Class III male were randomly presented to 24 subjects who were asked to indicate: 1) acceptability by pressing a mouse button and releasing the button when the images were no longer acceptable; and 2) most-pleasing image by pressing the mouse button once.

RESULTS

No differences were found between left- and right-profile images for zone of acceptability, midpoint of the zone of acceptability, or most pleasing; nor was there any relation to laterality measures. However, consistently higher intercorrelations among the features for the zone of acceptability were found for the left- than for the right-facing profiles for retrusive to protrusive and protrusive to retrusive excursions measured in millimeters (p < .001). The bimaxillary position accounted for most of the variance in judgments of acceptability with greater influence on the left than on the right profile.

CONCLUSION

With the increasing use of computer-imaging in dental practices, the influence of psychophysical and other environmental variables on perception must be considered.

Preference for the half-left profile pose: three inclusive models

Kinsbourne's hemispheric activation model and infant habitual-postural constraints may help explain the preference for the half-left profile.