Sex differences in face gender recognition in humans

Visual kin recognition in nonhuman primates: (Pan troglodytes and Macaca mulatta): inbreeding avoidance or male distinctiveness?

Faces provide important information about identity, age, and even kinship. A previous study in chimpanzees reported greater similarity between the faces of mothers and sons compared with mothers and daughters, or unrelated individuals. This was interpreted as an inbreeding avoidance mechanism where females, the dispersing gender, should avoid mating with any male that resembles their mother. Alternatively, male faces may be more distinctive than female faces, biasing attention toward males. To test these hypotheses, chimpanzees and rhesus monkeys matched conspecifics' faces of unfamiliar mothers and fathers with their sons and daughters. Results showed no evidence of male distinctiveness, rather a cross-gender effect was found: chimpanzees were better matching moms with sons and fathers with daughters. Rhesus monkeys, however, showed an overwhelming bias toward male-distinctiveness. They were faster to learn male faces, performed better on father-offspring and parent-son trials, and were best matching fathers with sons. This suggests that for the rhesus monkey, inbreeding avoidance involves something other than facial phenotypic matching but that among chimpanzees, the visual recognition of facial similarities may play an important role.

Dogs can discriminate human smiling faces from blank expressions

Dogs have a unique ability to understand visual cues from humans. We investigated whether dogs can discriminate between human facial expressions. Photographs of human faces were used to test nine pet dogs in two-choice discrimination tasks. The training phases involved each dog learning to discriminate between a set of photographs of their owner's smiling and blank face. Of the nine dogs, five fulfilled these criteria and were selected for test sessions. In the test phase, 10 sets of photographs of the owner's smiling and blank face, which had previously not been seen by the dog, were presented. The dogs selected the owner's smiling face significantly more often than expected by chance. In subsequent tests, 10 sets of smiling and blank face photographs of 20 persons unfamiliar to the dogs were presented (10 males and 10 females). There was no statistical difference between the accuracy in the case of the owners and that in the case of unfamiliar persons with the same gender as the owner. However, the accuracy was significantly lower in the case of unfamiliar persons of the opposite gender to that of the owner, than with the owners themselves. These results suggest that dogs can learn to discriminate human smiling faces from blank faces by looking at photographs. Although it remains unclear whether dogs have human-like systems for visual processing of human facial expressions, the ability to learn to discriminate human facial expressions may have helped dogs adapt to human society.

Attention, response inhibition, and face-information processing in children: the role of task characteristics, age, and gender

The aim of the study was to assess: (a) developmental changes in attention, response inhibition, and face-information processing using the new Balloons task and (b) to evaluate the association between measures derived from the task with reported behavior problems. One hundred and thirty-four typically developing children (53 boys and 81 girls) were tested with the Balloons. Their parents and teachers completed the Child Behavior Checklist. Our results validate the Balloons as a reliable task with significant effects of manipulations in difficulty level (speed, processing load, and processing type). The results suggest that face-information processing undergoes significant changes during the age period between 7 and 13 years with significant gender differences. Modest but significant correlations were found between the Balloons' measures and behavior problems.

Social anxiety disorder women easily recognize fearfull, sad and happy faces: the influence of gender

BACKGROUND

It has been suggested that individuals with social anxiety disorder (SAD) are exaggeratedly concerned about approval and disapproval by others. Therefore, we assessed the recognition of facial expressions by individuals with SAD, in an attempt to overcome the limitations of previous studies.

METHODS

The sample was formed by 231 individuals (78 SAD patients and 153 healthy controls). All individuals were treatment naïve, aged 18-30 years and with similar socioeconomic level. Participants judged which emotion (happiness, sadness, disgust, anger, fear, and surprise) was presented in the facial expression of stimuli displayed on a computer screen. The stimuli were manipulated in order to depict different emotional intensities, with the initial image being a neutral face (0%) and, as the individual moved on across images, the expressions increased their emotional intensity until reaching the total emotion (100%). The time, accuracy, and intensity necessary to perform judgments were evaluated.

RESULTS

The groups did not show statistically significant differences in respect to the number of correct judgments or to the time necessary to respond. However, women with SAD required less emotional intensity to recognize faces displaying fear (p=0.002), sadness (p=0.033) and happiness (p=0.002), with no significant differences for the other emotions or men with SAD.

CONCLUSIONS

The findings suggest that women with SAD are hypersensitive to threat-related and approval-related social cues. Future studies investigating the neural basis of the impaired processing of facial emotion in SAD using functional neuroimaging would be desirable and opportune.

Sex differences in face gender recognition: an event-related potential study

Multiple level neurocognitive processes are involved in face processing in humans. The present study examined whether the early face processing such as structural encoding is modulated by task demands that manipulate attention to perceptual or social features of faces and such an effect, if any, is different between men and women. Event-related brain potentials were recorded from male and female adults while they identified a low-level perceptual feature of faces (i.e., face orientation) and a high-level social feature of faces (i.e., gender). We found that task demands that required the processing of face orientations or face gender resulted in modulations of both the early occipital/temporal negativity (N170) and the late central/parietal positivity (P3). The N170 amplitude was smaller in the gender relative to the orientation identification task whereas the P3 amplitude was larger in the gender identification task relative to the orientation identification task. In addition, these effects were much stronger in women than in men. Our findings suggest that attention to social information in faces such as gender modulates both the early encoding of facial structures and late evaluative process of faces to a greater degree in women than in men.

A socio-relational framework of sex differences in the expression of emotion

Despite a staggering body of research demonstrating sex differences in expressed emotion, very few theoretical models (evolutionary or non-evolutionary) offer a critical examination of the adaptive nature of such differences. From the perspective of a socio-relational framework, emotive behaviors evolved to promote the attraction and aversion of different types of relationships by advertising the two most parsimonious properties of reciprocity potential, or perceived attractiveness as a prospective social partner. These are the individual's (a) perceived capacity or ability to provide expedient resources, or to inflict immediate harm onto others, and their (b) perceived trustworthiness or probability of actually reciprocating altruism (Vigil 2007). Depending on the unique social demands and relational constraints that each sex evolved, individuals should be sensitive to advertise "capacity" and "trustworthiness" cues through selective displays of dominant versus submissive and masculine versus feminine emotive behaviors, respectively. In this article, I introduce the basic theoretical assumptions and hypotheses of the framework, and show how the models provide a solid scaffold with which to begin to interpret common sex differences in the emotional development literature. I conclude by describing how the framework can be used to predict condition-based and situation-based variation in affect and other forms of expressive behaviors.

Gender related differences in visual and auditory processing of verbal and figural tasks

The aim of the present study was to investigate gender related differences in brain activity for tasks of verbal and figural content presented in the visual and auditory modality. Thirty male and 30 female respondents solved four tasks while their electroencephalogram (EEG) was recorded. Also recorded was the percentage of oxygen saturation of hemoglobin (%StO(2)) in the respondents' frontal brain areas with near-infrared spectroscopy (NIRS). The main findings of the study can be summarized as follows. (1) Most pronounced differences between males and females were observed for the factor modality-visual/auditory. (2) Gender related differences in neuroelectric brain responses could be observed during the solution of auditory and visual tasks; however, on the behavioral level only for the visual tasks did females display shorter reaction times than males. The ERP amplitudes of the early evoked gamma response, P1, and P3 were higher in females than males, whereas the N4 amplitude was higher in males than females. The differences were more noticeable in the visual modality. The NIRS showed a more bilateral involvement of the frontal brain areas in females as compared with a more left hemispheric frontal activity in males. In the task conditions an increase in right hemispheric activity in females was observed; however, this increase was less pronounced in the visual than the auditory domain, indicating a more lateralized processing of visual stimuli in females. Taken all together the results suggest that the females' visual event-categorization process is more efficient than in males.

Cortical responses to self and others

The extrastriate body area (EBA) is one among the multiple, functionally specialized regions of the human visual cortex exhibiting modulation by body-related stimuli. Here we investigate whether activation patterns differ for the perception of one's own body and the bodies of others. We used functional magnetic resonance imaging to identify body-related brain areas and to see how these areas differentiate between images of one's own body and those of others in the absence of facial or motion cues. Whole brain explorative group-level analysis identified body-related blood oxygen level dependent (BOLD) signal enhancement in five regions of the right and in one region of the left hemisphere (right: in the extrastriate visual and parietal cortex and in the precentral gyrus, left: in the extrastriate visual cortex). General linear model group-level random effects analysis of the self-other contrast revealed self-related responses in the extrastriate and parietal regions in the right hemisphere but also in the right middle frontal gyrus. These results suggest the existence of a cortical network for the extraction of body-related information and another cortical network for the extraction of self-related body information. The two networks partially overlap in the right superior and inferior parietal cortices, but are clearly segregated in the extrastriate visual cortex and in the middle frontal gyrus. In addition, we report that the classical EBA is only involved in the analysis of body-related information but not in the assignment of body identity. The latter appears to be accomplished by a network in right hemisphere comprising the fusiform body area, regions of the superior parietal lobe, the inferior parietal cortex, and the middle frontal gyrus.

A bias for the female face in the right hemisphere

In the present study we assessed the contribution of the two hemispheres to the attribution of gender of faces in male and female observers. Normal and chimeric faces were presented in their canonical orientation and upside-down in a tachistoscopic paradigm. Chimeric faces were composed of two halves (left and right) obtained from photos of individuals of the same sex or from individuals of different sexes. All faces were presented tachistoscopically with a central fixation, the two halves falling in the two visual fields of the observer, who was required to rapidly judge the sex of the face. A left half-face (right-hemispheric) bias for gender attribution with upright faces was observed both in male and female participants, as previously reported. Strikingly, however, the bias depended entirely on female-left/male-right chimeras, revealing a right-hemispheric advantage for the recognition of female faces. The results are discussed in the light of a behavioural bias during development (i.e., maternal cradling).

Recognition of facial emotion in low vision: a flexible usage of facial features

Age-related macular degeneration (AMD) is a major cause of visual impairment in people older than 50 years in Western countries, affecting essential tasks such as reading and face recognition. Here we investigated the mechanisms underlying the deficit in recognition of facial expressions in an AMD population with low vision. Pictures of faces displaying different emotions with the mouth open or closed were centrally displayed for 300 ms. Participants with AMD with low acuity (mean 20/200) and normally sighted age-matched controls performed one of two emotion tasks: detecting whether a face had an expression or not (expressive/non expressive (EXNEX) task) or categorizing the facial emotion as happy, angry, or neutral (categorization of expression (CATEX) task). Previous research has shown that healthy observers are mainly using high spatial frequencies in an EXNEX task while performance at a CATEX task was preferentially based on low spatial frequencies. Due to impaired processing of high spatial frequencies in central vision, we expected and observed that AMD participants failed at deciding whether a face was expressive or not but categorized normally the emotion of the face (e.g., happy, angry, neutral). Moreover, we observed that AMD participants mostly identified emotions using the lower part of the face (mouth). Accuracy did not differ between the two tasks for normally sighted observers. The results indicate that AMD participants are able to identify facial emotion but must base their decision mainly on the low spatial frequencies, as they lack the perception of finer details.

Gender differences influence brain's beta oscillatory responses in recognition of facial expressions

There are only few studies describing gender differences in recognition of facial expressions. Our study has the aim to analyze the effect of gender differences in oscillatory brain responses. Three sets of Ekman and Friesens's facial expressions (neutral, angry, and happy) were presented to 26 healthy subjects (13 men) while recording from 13 different scalp locations. Occipital beta response (15-24Hz) was significantly larger for women than for men during the presentation of face expressions. Our results demonstrate that processing of emotional face expressions clearly differs between men and women. Accordingly, the results indicate the necessity of introducing standardization between male and female subjects by means of oscillatory dynamics. In turn, this standardization may be useful for cognitive and clinical studies.

Neurophysiological correlates for the perception of facial sexual dimorphism

Neural correlates for the processing of face identity, expression, gaze direction and attractiveness are well described, but neurophysiological correlates for the perception of face gender are less understood. Here, we used morphing techniques to produce synthetic faces with graded perceivable gender and independent component analysis (ICA) of multifocal EEG to unravel neural signals correlated to processing and perception of face gender. We investigate possible neural correlates of face perception using scalp event-related potentials (ERPs) and dipole source analysis in a group of health observers. We isolated one signal source localised to the right parieto-temporal region with a latency of about 170 ms, whose latency correlates with perceived facial masculinity. In conclusion, our data prove that the right parieto-temporal regions play a fundamental role in face gender masculinity processing and perception in humans.

Gender and parental status affect the visual cortical response to infant facial expression

This study sought to determine the influence of gender and parental status on the brain potentials elicited by viewing infant facial expressions. We used ERP recording during a judgement task of infant happy/distressed expression to investigate if viewer gender or parental status affects the visual cortical response at various stages of perceptual processing. ERPs were recorded in 38 adults (male/female, parents/non-parents) during processing of infant facial expressions that varied in valence and intensity. All infants were unfamiliar to viewers. The lateral occipital P110 response was much larger in women than in men, regardless of facial expression, thus indicating a gender difference in early visual processing. The occipitotemporal N160 response provided the first evidence of discrimination of expressions of discomfort and distress and demonstrated a significant gender difference within the parent group, thus suggesting a strong interactive influence of genetic predisposition and parental status on the responsivity of visual brain areas. The N245 component exhibited complete coding of the intensity of facial expression, including positive expressions. At this processing stage the cerebral responses of female and male non-parents were significantly smaller than those of parents and insensitive to differences in the intensity of infant suffering. Smaller P300 amplitudes were elicited in mothers versus fathers, especially with infant expressions of suffering. No major group differences were observed in cerebral responses to happy or comfortable expressions. These findings suggest that mere familiarity with infant faces does not explain group differences.