Representation of Faces in Longtailed Macaques (Macaca fascicularis)

The experiments described in this study were intended to increase our knowledge about social cognition in primates. Longtailed macaques (Macaca fascicularis) had to discriminate facial drawings of different emotional expressions. A new experimental approach was used. During the experimental sessions social interactions within the group were permitted, but the learning behaviour of individual monkeys was analysed. The procedure consisted of a simultaneous discrimination between four visual patterns under continuous reinforcement. It has implications not only for simple tasks of stimulus discrimination but also for complex problems of internal representations and visual communication. The monkeys learned quickly to discriminate faces of different emotional expressions. This discrimination ability was completely invariant with variations of colour, brightness, size, and rotation. Rotated and inverted faces were recognized perfectly. A preference test for particular features resulted in a graded estimation of particular facial components. Most important for face recognition was the outline, followed by the eye region and the mouth. An asymmetry in recognition of the left and right halves of the face was found. Further tests involving jumbled faces indicated that not only the presence of distinct facial cues but the specific relation of facial features is essential in recognizing faces. The experiment generally confirms that causal mechanisms of social cognition in non-human primates can be studied experimentally. The behavioural results are highly consistent with findings from neurophysiology and research with human subjects.     

Beauty hinders attention switch in change detection: the role of facial attractiveness and distinctiveness

Background

Recent research has shown that the presence of a task-irrelevant attractive face can induce a transient diversion of attention from a perceptual task that requires covert deployment of attention to one of the two locations. However, it is not known whether this spontaneous appraisal for facial beauty also modulates attention in change detection among multiple locations, where a slower, and more controlled search process is simultaneously affected by the magnitude of a change and the facial distinctiveness. Using the flicker paradigm, this study examines how spontaneous appraisal for facial beauty affects the detection of identity change among multiple faces.

Methodology/Principal Findings

Participants viewed a display consisting of two alternating frames of four faces separated by a blank frame. In half of the trials, one of the faces (target face) changed to a different person. The task of the participant was to indicate whether a change of face identity had occurred. The results showed that (1) observers were less efficient at detecting identity change among multiple attractive faces relative to unattractive faces when the target and distractor faces were not highly distinctive from one another; and (2) it is difficult to detect a change if the new face is similar to the old.

Conclusions/Significance

The findings suggest that attractive faces may interfere with the attention-switch process in change detection. The results also show that attention in change detection was strongly modulated by physical similarity between the alternating faces. Although facial beauty is a powerful stimulus that has well-demonstrated priority, its influence on change detection is easily superseded by low-level image similarity. The visual system appears to take a different approach to facial beauty when a task requires resource-demanding feature comparisons.     

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.     

Denture Wearer's Self Assessment of Vertical Dimension

Two groups of complete denture wearers were used. They were informed about normal facial proportions and were then asked to classify themselves into one of four face height classes. One group had to choose between four schematic drawings and the other between four color photos of a complete denture wearer, taken at different vertical dimensions. The patients' self-assessment was correlated to a professional assessment and measurements of the patients' face. The patients' assessments were significantly correlated to the professional assessment in both groups. Self assessment of facial proportions by complete denture wearers could be an easy and useful method of activating them to consult a dentist for check-up. The simple drawings were found to be most suitable.     

Denture Wearers' Awareness of their Vertical Dimension

A method of analyzing facial proportions in evaluating occlusal vertical dimension was used in a test on 71 complete denture wearers aiming to find a way to rank denture wearers with different stages of reduced vertical dimension and development an instruction for patients' self judgment. By use of face drawings on a proforma the patients ranked themselves into one of four classes. The investigator also ranked the patients into these classes. There was a significant correlation (p<0.01) between the ranking by patient and investigator. The face proportions were also measured with an instrument. The distances nasion-rima oris and subnasale-gnathion were established. When ranking into classes, there was a significant (p<0.0001) correlation between the ranking by the investigator and the measurements. The results show that it may be possible to use information of facial proportions to give complete denture wearers a way of assessment of face height and thus a reason to consult a dentist in case of suspicion of reduced vertical dimension.     

Facial Expression Aftereffect Revealed by Adaption to Emotion-Invisible Dynamic Bubbled Faces

Visual adaptation is a powerful tool to probe the short-term plasticity of the visual system. Adapting to local features such as the oriented lines can distort our judgment of subsequently presented lines, the tilt aftereffect. The tilt aftereffect is believed to be processed at the low-level of the visual cortex, such as V1. Adaptation to faces, on the other hand, can produce significant aftereffects in high-level traits such as identity, expression, and ethnicity. However, whether face adaptation necessitate awareness of face features is debatable. In the current study, we investigated whether facial expression aftereffects (FEAE) can be generated by partially visible faces. We first generated partially visible faces using the bubbles technique, in which the face was seen through randomly positioned circular apertures, and selected the bubbled faces for which the subjects were unable to identify happy or sad expressions. When the subjects adapted to static displays of these partial faces, no significant FEAE was found. However, when the subjects adapted to a dynamic video display of a series of different partial faces, a significant FEAE was observed. In both conditions, subjects could not identify facial expression in the individual adapting faces. These results suggest that our visual system is able to integrate unrecognizable partial faces over a short period of time and that the integrated percept affects our judgment on subsequently presented faces. We conclude that FEAE can be generated by partial face with little facial expression cues, implying that our cognitive system fills-in the missing parts during adaptation, or the subcortical structures are activated by the bubbled faces without conscious recognition of emotion during adaptation.     

Facial Skin Coloration Affects Perceived Health of Human Faces

Numerous researchers have examined the effects of skin condition, including texture and color, on the perception of health, age, and attractiveness in human faces. They have focused on facial color distribution, homogeneity of pigmentation, or skin quality. We here investigate the role of overall skin color in determining perceptions of health from faces by allowing participants to manipulate the skin portions of color-calibrated Caucasian face photographs along CIELab color axes. To enhance healthy appearance, participants increased skin redness (a*), providing additional support for previous findings that skin blood color enhances the healthy appearance of faces. Participants also increased skin yellowness (b*) and lightness (L*), suggesting a role for high carotenoid and low melanin coloration in the healthy appearance of faces. The color preferences described here resemble the red and yellow color cues to health displayed by many species of nonhuman animals.     

Histological studies of the dorsal nasal,Angularis Oculi,and facial veins of sheep (Ovis aries)

Selective brain cooling (SBC) requires vasoactivity in the superficial veins of the face of the animal. This vasoactivity is possible because of an adequate amount of smooth muscle in the tunica media of each of these superficial vessels, enabling it to act as a “muscle sphincter.” In this study, the angularis oculi, dorsal nasal, distal, and proximal parts of the facial veins in sheep were examined histologically to describe an anatomical basis for SBC. Measurements of the tunica media thickness, the lumen diameter, and the ratio of these measurements showed that the relative tunica media thicknesses in the angularis oculi vein and the dorsal nasal vein are statistically smaller (P < 0.001) than in the distal or the proximal parts of the facial vein. In the angularis oculi, dorsal nasal, and distal part of the facial vein, the tunicae mediae were composed of five to seven circularly arranged smooth muscle layers, suggesting their ability to vasoconstrict. The proximal part of the facial vein possesses both circularly and longitudinally arranged smooth muscle layers. The circular smooth muscle layers suggest a vasoconstrictory function, whereas the longitudinal smooth muscle layers imply a vasodilatory function in this part of the facial vein. Both the dorsal nasal and the proximal part of the facial vein, but not the angularis oculi or the distal part of the facial vein, possess endothelial valves near their confluences with other veins. It was concluded from this study that the angularis oculi and the distal part of the facial vein vasoconstrict, whereas the proximal part of the facial vein vasodilates, enabling the necessary changes in blood flow in SBC. J. Morphol. 237:275–281, 1998. © 1998 Wiley-Liss, Inc.     

Specialized visual learning of facial signals of quality in the paper wasp,Polistes dominula

Some primates and one species of paper wasp recognize faces using specific processing strategies to extract individual identity information from conspecific faces. Explanations for the evolution of face specialization typically focus on the complexity associated with individual recognition because all currently identified species with face specialization use faces for individual recognition. In the present study, we show an independent evolution of face specialization in a paper wasp species with facial patterns that signal quality rather than individual identity. Quality signals are simpler to process than individual identity signals because quality signals do not require simultaneous integration across multiple stimuli or learning and memory. Therefore, the results of the present study suggest that the complexity of processing may not be the key factor favouring the evolution of specialization. Instead, the predictable location of socially important signals relative to other anatomical features may allow easy categorization of features, thereby favouring specialized visual processing. Given that visual quality signals are found in many taxa, specific‐processing mechanisms for social signals may be widespread. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 992–997.     

How is the individuality of a face recognized?

A familiar face is instantly recognized in a crowd. This cannot be achieved through a feature by feature comparison of the observed face with either an average face (norm-based model of face recognition) or with a set of similarly constructed faces stored in memory (exemplar-based model of face recognition). A modified norm-based model is thus proposed. Instead of memorizing an average face, the normal variations for each facial feature are used to construct a multidimensional volume of face-space devoid of unusual features, here defined as features whose metrics lie below the 5th or above the 95th percentiles for that feature. A face consisting of 100 independently variable features will thus have, on average, 10 unusual features. Face identification then becomes exception-reporting. It requires only 10 such rare features to render a given face a one in 10¹³ faces (P=0.05¹⁰=9.8×10⁻¹⁴). In a world containing 6.7×10⁹ people, such a face would be unique. Faces remembered in this way can have their unusual features exaggerated or attenuated without loss of identity. This is the basis of caricatures and anti-caricatures. It also means that individuals belonging to a foreign race, possessing several features with modes beyond the “usual range” of the own-race population, will all look alike. Features that render a face unique in the own-race population are now shared by everyone in the foreign race.Average faces are more beautiful than the faces used in the averaging process. This makes evolutionary sense. Natural selection increases the frequency of fit features at the expense of maladaptive features. “Usual features” are therefore fitter than “unusual features”, and play an important role in mate selection. Such an existing fundamental sexual attribute could easily have been harnessed for the fast and efficient recognition of individuals in the community.     

Scanning Strategies Do Not Modulate Face Identification: Eye-Tracking and Near-Infrared Spectroscopy Study

Background

During face identification in humans, facial information is sampled (seeing) and handled (processing) in ways that are influenced by the kind of facial image type, such as a self-image or an image of another face. However, the relationship between seeing and information processing is seldom considered. In this study, we aimed to reveal this relationship using simultaneous eye-tracking measurements and near-infrared spectroscopy (NIRS) in face identification tasks.

Methodology/Principal Findings

22 healthy adult subjects (8 males and 14 females) were shown facial morphing movies in which an initial facial image gradually changed into another facial image (that is, the subject''s own face was changed to a familiar face). The fixation patterns on facial features were recorded, along with changes in oxyhemoglobin (oxyHb) levels in the frontal lobe, while the subjects identified several faces. In the self-face condition (self-face as the initial image), hemodynamic activity around the right inferior frontal gyrus (IFG) was significantly greater than in the familiar-face condition. On the other hand, the scanning strategy was similar in almost all conditions with more fixations on the eyes and nose than on other areas. Fixation time on the eye area did not correlate with changes in oxyHb levels, and none of the scanning strategy indices could estimate the hemodynamic changes.

Conclusions/Significance

We conclude that hemodynamic activity, i.e., the means of processing facial information, is not always modulated by the face-scanning strategy, i.e., the way of seeing, and that the right IFG plays important roles in both self-other facial discrimination and self-evaluation.     

Technical note: Different techniques,different results—a comparison of photogrammetric and caliper-derived measurements

The primary goal of our study was to compare photogrammetric measurements with caliper-derived measurements. We also looked at the difference between caliper-derived measurements that were taken with and without the landmarks marked. Thirteen facial measurements were repeated ten times on two adult subjects as follows: 1) Calipers were used to take the measurements before the landmarks were marked on each subject's face; 2) the landmarks were then marked with a black pencil, and the calipers were used to take the measurements again; and 3) images were taken of each subject with the markings left on the face, and the measurements were extracted from these images. Compared with the caliper-derived data taken with the landmarks marked, the photogrammetric means and standard deviations were typically larger, leading us to conclude that there was a systematic difference between the data. The generally greater variation in the photogrammetric measurements was ascribed to poor conditions, such as shadows, oblique markings, and unmarked landmarks. When the data gathered by caliper with and without the landmarks marked were compared, a systematic difference was suggested by the number of statistically significant t-test probabilities. Marking the landmarks reduced the standard deviations in some measurements by controlling two sources of variation: differing pressure on the skin and slippage of the calipers. Anthropologists, medical geneticists, and others who use measurements for diagnostic or classificatory purposes should be aware that data gathered by different techniques may yield different results. Am J Phys Anthropol 106:547–552, 1998. © 1998 Wiley-Liss, Inc.     

Recognition of facial expressions in a Japanese monkey (Macaca fuscata) and humans (Homo sapiens)

Recognition of facial expressions by a Japanese monkey and two humans was studied. The monkey subject matched 20 photographs of monkey facial expressions and 20 photographs of human facial expressions. Humans sorted the same pictures. Matching accuracy by the monkey was about 80% correct for both human and monkey facial expressions. The confusion matrices of those facial expressions were analyzed by a multi-dimensional scaling procedure (MDSCAL). The resulting MDS plots suggested that the important cues in recognizing facial expressions of monkeys were “thrusting the mouth” and ‘raising the eyebrows.” Comparison of the MDS plots by the monkey subject with those by human subjects suggested that the monkey categorized the human “happiness” faces. This may suggest that the monkey has an ability to recognize human smile face even though it is learned. However, the monkey did not differentiate the human “anger/disgust” faces from the human “sad” faces, while human subjects clearly did. This may correlate with the lack of eyebrow movement in monkeys.     

Is beauty in the eye of the beholder?

Theories of beauty were evaluated by requiring subjects to “evolve” a beautiful female face using a Genetic Algorithm. In this procedure, a computer program generated a small population of faces (first generation of phenotypes) from a set of random binary strings (genotypes). Genotypes specified the shapes and soft tissue anthropometrics of facial features. Each of the first generation of faces was rated by a subject (relative fitness measure) for beauty. The fittest genotypes then bred in proportion to their fitness, with crossover and mutation of the binary strings, to produce offspring which were again rated by the subject. This process continued until the most beautiful face, for that subject, was evolved. Forty Caucasian subjects (20 M, 20 F) were required to evolve their idealized beautiful female face using this procedure. The features and soft tissue anthropometrics of their final composites were compared to population norms. Also, the final composites, and different faces generated from the same data base, were rated for beauty by independent judges. The results support the conclusion that the concept of facial beauty is the result of sexual selection, and a beautiful female face has features and proportions indicative on high fertility.     

Japanese macaques form a cross-modal representation of their own species in their first year of life

We tested whether infant Japanese macaques (Macaca fuscata) have a cross-modal representation of their own species. We presented monkeys with a photograph of either a monkey or a human face on an LCD monitor after playing back a vocalization of one of those two species. The subjects looked at the monitor longer when a human face was presented after the monkey vocalization than when the same face was presented after human vocalization. This suggests that monkeys recall and expect a monkey’s face upon hearing a monkey’s voice.     

Eye gaze during observation of static faces in deaf people

Knowing where people look when viewing faces provides an objective measure into the part of information entering the visual system as well as into the cognitive strategy involved in facial perception. In the present study, we recorded the eye movements of 20 congenitally deaf (10 male and 10 female) and 23 (11 male and 12 female) normal-hearing Japanese participants while they evaluated the emotional valence of static face stimuli. While no difference was found in the evaluation scores, the eye movements during facial observations differed among participant groups. The deaf group looked at the eyes more frequently and for longer duration than the nose whereas the hearing group focused on the nose (or the central region of face) more than the eyes. These results suggest that the strategy employed to extract visual information when viewing static faces may differ between deaf and hearing people.     

Trisomy 21 and facial developmental instability

The most common live‐born human aneuploidy is trisomy 21, which causes Down syndrome (DS). Dosage imbalance of genes on chromosome 21 (Hsa21) affects complex gene‐regulatory interactions and alters development to produce a wide range of phenotypes, including characteristic facial dysmorphology. Little is known about how trisomy 21 alters craniofacial morphogenesis to create this characteristic appearance. Proponents of the "amplified developmental instability" hypothesis argue that trisomy 21 causes a generalized genetic imbalance that disrupts evolutionarily conserved developmental pathways by decreasing developmental homeostasis and precision throughout development. Based on this model, we test the hypothesis that DS faces exhibit increased developmental instability relative to euploid individuals. Developmental instability was assessed by a statistical analysis of fluctuating asymmetry. We compared the magnitude and patterns of fluctuating asymmetry among siblings using three‐dimensional coordinate locations of 20 anatomic landmarks collected from facial surface reconstructions in four age‐matched samples ranging from 4 to 12 years: 1) DS individuals (n = 55); 2) biological siblings of DS individuals (n = 55); 3) and 4) two samples of typically developing individuals (n = 55 for each sample), who are euploid siblings and age‐matched to the DS individuals and their euploid siblings (samples 1 and 2). Identification in the DS sample of facial prominences exhibiting increased fluctuating asymmetry during facial morphogenesis provides evidence for increased developmental instability in DS faces. We found the highest developmental instability in facial structures derived from the mandibular prominence and lowest in facial regions derived from the frontal prominence. Am J Phys Anthropol 151:49–57, 2013. © 2013 Wiley Periodicals, Inc.     

Familiar Face Detection in 180ms

The visual system is tuned for rapid detection of faces, with the fastest choice saccade to a face at 100ms. Familiar faces have a more robust representation than do unfamiliar faces, and are detected faster in the absence of awareness and with reduced attentional resources. Faces of family and close friends become familiar over a protracted period involving learning the unique visual appearance, including a view-invariant representation, as well as person knowledge. We investigated the effect of personal familiarity on the earliest stages of face processing by using a saccadic-choice task to measure how fast familiar face detection can happen. Subjects made correct and reliable saccades to familiar faces when unfamiliar faces were distractors at 180ms—very rapid saccades that are 30 to 70ms earlier than the earliest evoked potential modulated by familiarity. By contrast, accuracy of saccades to unfamiliar faces with familiar faces as distractors did not exceed chance. Saccades to faces with object distractors were even faster (110 to 120 ms) and equivalent for familiar and unfamiliar faces, indicating that familiarity does not affect ultra-rapid saccades. We propose that detectors of diagnostic facial features for familiar faces develop in visual cortices through learning and allow rapid detection that precedes explicit recognition of identity.     

Baboons (Papio papio) spontaneously process the first-order but not second-order configural properties of faces

A two-alternative forced-choice discrimination task was used to assess whether baboons (N=7) spontaneously process qualitative (i.e., first-order) or quantitative (i.e., second-order) variations in the configural arrangement of facial features. Experiment 1 used as test stimuli second-order pictorial faces of humans or baboons in which the mouth and the eyes were rotated upside down relative to the normal face. Baboons readily discriminated two different normal faces but did not discriminate a normal face from its second-order modified version. Experiment 2 used human or baboon faces for which the first-order configural properties had been distorted by reversing the location of the eyes and mouth within the face. Discrimination was prompt with these stimuli. Experiment 3 replicated some of the conditions and the results of experiment 1, thus ruling out possible effects of learning. It is concluded that baboons are more adept at spontaneously processing first- than second-order configural facial properties, similar to what is known in the human developmental literature.     

First partial face and upper dentition of the Middle Miocene hominoid Dryopithecus fontani from Abocador de Can Mata (Vallès‐Penedès Basin,Catalonia, NE Spain): Taxonomic and phylogenetic implications

A well‐preserved 11.8‐million‐years‐old lower face attributed to the seminal taxon Dryopithecus fontani (Primates, Hominidae) from the Catalan site ACM/C3‐Ae of the Hostalets de Pierola area (Vallès‐Penedès Basin, Catalonia, NE Spain) is described. The new data indicate that D. fontani is distinct at the genus level from Late Miocene European taxa previously attributed to Dryopithecus, which are here reassigned to Hispanopithecus. The new facial specimen also suggests that D. fontani and the Middle Miocene Pierolapithecus catalaunicus are not synonymous. Anatomical and morphometric analyses further indicate that the new specimen shows a combination of lower facial features—hitherto unknown in Miocene hominoids—that resembles the facial pattern of Gorilla, thus providing the first nondental evidence of gorilla‐like lower facial morphology in the fossil record. Considering the current evidence, the gorilla‐like facial pattern of D. fontani is inferred to be derived relative to previously known stem hominids, and might indicate that this taxon is either an early member of the Homininae or, alternatively, a stem hominid convergent with the lower facial pattern of Gorilla. The biogeographic implications of both alternatives are discussed. This new finding in the Hostalets de Pierola section reinforces the importance of this area for understanding the elusive question of the Middle Miocene origin and early radiation of great apes. Am J Phys Anthropol, 2009. © 2009 Wiley‐Liss, Inc.