Sex differences in face processing are mediated by handedness and sexual orientation

Functional lateralization in social-emotional processing: The influence of sexual orientation and gender identity on cradling preferences

The left-cradling bias (i.e., the motor asymmetry for cradling infants on the left side) has often been associated to the right-hemispheric social-emotional specialization, and it has often been reported to be stronger in females than in males. In this study we explored the effects of sexual orientation and gender identity on this lateral bias by means of a web-based investigation in a sample of adults (485 biological females and 196 biological males) recruited through LGBTQIA+ networks and general university forums. We exploited a cradling imagery task to assess participants' cradling-side preference, and standardized questionnaires to assess participants' homosexuality (Klein Sexual Orientation Grid) and gender nonconformity (Gender Identity/Gender Dysphoria Questionnaire for Adults and Adolescents). Results confirmed the expected left-cradling bias across all sexual orientation groups except for heterosexual males. Importantly, higher homosexuality scores were associated with higher proportions of left cradling in males. These results suggest that sexual orientation can influence cradling preference in males, indicating a complex interaction between biological and psychological factors in the laterality of social-emotional processing. Finally, the left-cradling bias seems to confirm its role as a behavioral proxy of social-emotional functional lateralization in humans.

Sexual Dimorphism in Hemispheric Processing of Faces in Humans: A Meta-Analysis of 817 Cases

A well-established neuroimaging literature predicts a right-sided asymmetry in the activation of face-devoted areas such as the fusiform gyrus (FG) and its resulting M/N170 response during face processing. However, the face-related response sometimes appears to be bihemispheric. A few studies have argued that bilaterality depended on the sex composition of the sample. To shed light on this matter, two meta-analyses were conducted starting from a large initial database of 250 ERP (Event-related potentials)/MEG (Magnetoencephalography) peer-reviewed scientific articles. Paper coverage was from 1985 to 2020. Thirty-four articles met the inclusion criteria of a sufficiently large and balanced sample size with strictly right-handed and healthy participants aged 18–35 years and N170 measurements in response to neutral front view faces at left and right occipito/temporal sites. The data of 817 male (n = 414) and female (n = 403) healthy adults were subjected to repeated-measures analyses of variance. The results of statistical analyses from the data of 17 independent studies (from Asia, Europe and America) seem to robustly indicate the presence of a sex difference in the way the two cerebral hemispheres process facial information in humans, with a marked right-sided asymmetry of the bioelectrical activity in males and a bilateral or left-sided activity in females.

An event-related potential comparison of facial expression processing between cartoon and real faces

Faces play important roles in the social lives of humans. Besides real faces, people also encounter numerous cartoon faces in daily life which convey basic emotional states through facial expressions. Using event-related potentials (ERPs), we conducted a facial expression recognition experiment with 17 university students to compare the processing of cartoon faces with that of real faces. This study used face type (real vs. cartoon), emotion valence (happy vs. angry) and participant gender (male vs. female) as independent variables. Reaction time, recognition accuracy, and the amplitudes and latencies of emotion processing-related ERP components such as N170, VPP (vertex positive potential), and LPP (late positive potential) were used as dependent variables. The ERP results revealed that cartoon faces caused larger N170 and VPP amplitudes as well as a briefer N170 latency than did real faces; that real faces induced larger LPP amplitudes than did cartoon faces. In addition, the results showed a significant difference in the brain regions as reflected in a right hemispheric advantage. The behavioral results showed that the reaction times for happy faces were shorter than those for angry faces; that females showed a higher accuracy than did males; and that males showed a higher recognition accuracy for angry faces than happy faces. Due to the sample size, these results may suggestively but not rigorously demonstrate differences in facial expression recognition and neurological processing between cartoon faces and real faces. Cartoon faces showed a higher processing intensity and speed than real faces during the early processing stage. However, more attentional resources were allocated for real faces during the late processing stage.

A Pilot Study on Tamoxifen Sexual Side Effects and Hand Preference in Male Breast Cancer

Recent clinical and imaging studies suggest that sex hormones modulate sexuality according to a psychophysiologic process of lateralization of the brain, with androgens playing a greater role in sexual functioning of left hemibrain/right handedness and estrogens possibly for right hemibrain/left handedness. Based on this perspective, the current study attempted to specify the relationship between hand preference, estrogens, and sexual function in subjects with male breast cancer, taking into account the sexual side effects of tamoxifen as the agent for inhibiting estrogen action. Twenty-eight Romanian men-17 right-handed and 11 left-handed-undergoing treatment with tamoxifen for male breast cancer participated in this study. These men were assessed both prior to and during tamoxifen treatment using the International Index of Erectile Function, a standardized instrument used for the evaluation of various aspects of sexual functioning, including erectile function (EF), orgasmic function (OF), sexual desire (SD), and overall functioning (OF). A main effect for handedness was found on EF, OF, SD, and OS scales, with right-handed men showing higher functioning than left-handed men. Regarding interaction effects, the left-handed group of men showed greater decreased sexual functioning during tamoxifen (on three subscales: OF, SD, OS) compared to right-handed men. Further research should be conducted in order to support and refine this potential lateralized process of sexual neuromodulation within the brain.

Hemisphere Preference Test: psychometric properties and relations with academic performance among adolescents

The present study explored, in adolescents, the dimensionality (factorial structure), reliability (internal consistency and test-retest stability) and predictive validity (in relation with academic grades) of the Hemispheric Preference Test (HPT), a widely used self-report index of thinking styles among adults. A sample of 990 Spanish adolescents aged 10-14 completed HPT and reported their academic grades. Results indicated a two-factor structure for HPT that can be interpreted in terms of left- and right-Hemisphere Preference (HP). The two-factor structure was clearer in boys compared to girls. The internal consistency and test-retest at 6 and 12 months were satisfactory. Left-HP scores decreased with age whereas girls obtained a higher mean score on right-HP sub-scale. Finally, Left-HP accounted for a significant variance percentage on academic grades after controlling for age and sex. Results suggested that Spanish version of the HPT was effective and reliable among adolescents.

Own-age and own-sex biases in recognition of aged faces

It is surprising how easily we are able to recognize people whom we have not seen in many years, somehow compensating for the aging-related facial changes that occurred. We measured the limits of the ability to recognize faces across the lifespan by young versus old men and women. Images of five males and five females at young and middle ages were morphed in 10% increments to create aged face images across the lifespan. Fifty-eight participants (28 females) judged whether pairs of photographs were of the same or different identity. Women outperformed men for female faces, exhibiting a sex difference and own-sex bias. Additionally, older participants showed an own-age bias and outperformed their younger counterparts with older stimuli. It appears that the recognition of faces is affected by the own-age and own-sex biases, potentially allowing us to remember some people better than others, thus mediating our interaction with the world.