| Human face is a kind of rich visual stimulus that provide information about individual identities,gender,age,race,physical health,gaze direction,and expression.Compared with less attractive face,more attractive face activates the reward centers in the observer’s brain,which in turn makes viewers tend to attribute positive personality traits to beauty face owners in multiple contexts,and then give positive comments to beautiful face owners.Therefore,face attractiveness plays an invaluable role in human social life.Sexual dimorphism is an important biological factor that affects the facial attractiveness.Regarding the impact of sexual dimorphism on the perceptions of female facial attractiveness,the results of existing research are basically the same,that is,feminine female faces are more attractive.However,there is no agreement on the impact of sexual dimorphism on the perceptions of male facial attractiveness: Some researchers suggested that masculine male faces(MMF)were more attractive than the feminine male faces(FMF),while others believed that the FMF were more attractive than the MMF,and some researchers suggested that there is no significant difference between MMF and the FMF.The role of gender dimorphism in the perception bias of male face attraction is inconsistent.On the one hand,it may be due to the modulating effects of processing context,the observer’s own characteristics,and the target face materials.On the other hand,it may be because the different methods of operation of facialsexual dimorphism were inconsistent,and the research results of composite faces and real faces were also divergent.In this thesis,three studies and eight experiments were designed,and female observers were invited to participant our study.Composite male faces and real male faces were used as experimental stimuli,and combined with processing context,the observer’s own characteristics,and the face stimuli,systematically examined the effect of sexual dimorphism on the perception bias of male facial attractiveness.The first study focused on the effects of sexual dimorphism and processing context on the perception bias of male facial attractiveness;the second study examined the effects of sexual dimorphism and observers’ age on the perception bias of male facial attractiveness;the third study examined the influence of sexual dimorphism and face type(handsome vs.ordinary)on the perception bias of male facial attractiveness.Both study 1 and study 2 are behavioral experiments.On the basis of behavioral experiments,functional magnetic resonance(fMRI)was also used to record the brain activation characteristics of the perception bias of face images.Specifically,in the first study,Experiment 1(Composite face)and Experiment 2(real face)mainly examined the effects of sexual dimorphism and processing context(raising children)on the perception bias of male facial attractiveness;Experiment 3(Composite face)and Experiment 4(Real faces)mainly examined the effects of sexual dimorphism and relationship types(friends/mate)on the perception bias of male facial attractiveness.In the second study,Experiment 5(Composite face)and Experiment 6(Real Faces)focused on the effects of sexual dimorphism and observers’ age on the perception bias of male facial attractiveness.In the third study,Experiment 7(Composite face)and Experiment 8(Real Faces)focused on the effects of sexual dimorphism and face types(handsome and normal faces)on the perception bias of male facial attractiveness and brain activation characteristics.The main results of this thesis are as follows:(1)In the conditions of different processing context: when composite faces were used as experimental materials,the influence of sexual dimorphism on the perception bias of male facial attractiveness is modulated by the processing context.However,when the real face is used as the experimental material,the influence of sexual dimorphism on the perception bias of male facial attractiveness was not modulated by the processing context.Specifically,the results of Experiment 1 showed that female observers rated FFM more attractive than the MMF in the context of raising children were primed,while the control group rated MMF more attractive than the FMF.The results of Experiment 3 showed that female observers rated FMF more attractive than the MMF in the context of making friends,while rated the MMF more attractive than the FMF in the context of mating.Experiments 2 and 4 showed that regardless of whether the processing context of raising children or the processing context of making friends and mating,the female observer consistently rated the FMF more attractive than the MMF.(2)Under different female observer age groups: when using composite faces as experimental materials,the effect of sexual dimorphism on the perception bias of male facial attractiveness is modulated by the female observers’ age groups.However,when the real face is used as the experimental material,the influence of sexual dimorphism on the perception bias of male facial attractiveness was not modulated by the female observers’ age groups.Specifically,the results of Experiment 5 showed that for the FMF,the early adulthood group rated less attractive than the puberty group and the menopausal group,while the puberty group and the menopausal group did not have significant differences;for the MMF,the early adult group rated more attractive than the puberty group and the menopausal group,while there were no significant differences between the puberty group and the menopausal group.When using real faces as experimental materials,the effect of sexual dimorphism on the perception bias of male facial attractiveness was not modulated by the age factor of female observers.The results of Experiment 6 showed that the three groups of female observers agree that the FMF were significantly more attractive than the MMF.(3)Under different types of face conditions,when using composite faces as experimental materials,the results of Experiment 7 showed that for the handsome male faces,female observers rated MFF more attractive than the FMF;For normal male faces,female observations rated no significant difference in the attractiveness scores between the MMF and FMF.The handsome face significantly activates the left fusiform gyrus,right inferior frontal gyrus and left lingual gyrus areas than the normal face;the MMF significantly activates the left hippocampal area;the interaction between sexual dimorphism and face type significantly activates the left insula.While the real face was used as the experimental material,the results of Experiment 8 showed that the female observers considered the FMF attractiveness score to be significantly higher than the MMF,whether it was a handsome or normal male face.The handsome face significantly activated the bilateral fusiform gyrus,bilateral inferior frontal gyrus,and theleft middle Occipital gyrus than the normal face;FMF significantly activated the left superior medial frontal gyrus than the MMF;the interaction between sexual dimorphism and face type was not significant.In summary,our research showed that(1)when composite male face was used as experimental materials,the effect of sexual dimorphism on the perception bias of male facial attractiveness will be modulated by the processing context,observers’ age,and target face type factors.Although the results of the study were relatively complex,they generally supported the theory of multiple trade-offs,that is,female observers trade off the preference for MMF or FMF based on different conditions.(2)When the real male face was used as the experimental material,the influence of sexual dimorphism on the perception bias of male facial attractiveness was not modulated by the processing context,the age of the observer,and the target type of face.The results of the study were relatively uniform,that is,female observers rated FMF more attractive than MMF.This effect may be related to the cultural background of China.(3)In the fMRI experiment,for the composite face,the brain region activated by sexual dimorphism is the left hippocampus;for the real face,the brain region activated by gender dimorphism is the left superior medial frontal gyrus.Processing handsome and normal faces,both composite and real faces activate the left fusiform and right inferior frontal gyrus,but the processing of real faces activates a wider brain area than synthetic faces.Although the brain regions involved are all related to visual aesthetic experience,the reasons for such inconsistency need to be further explored in future studies.The main innovations of this thesis are as follows:(1)Investigating the influence mechanism of sexual dimorphism on the perception bias of male facial attractiveness in combination with processing context,observers’ age,and target face stimulus;(2)Comparing the experimental effects of two different types of face stimuli(i.e.,composite faces and real face),we found that the results of composite faces used in previous studies have not been verified under the real face conditions;(3)Developed a real face measurement tool for studying sexual dimorphism;(3)For the first time,fMRI technology was used to investigate the brain activation characteristics of sexual dimorphism in brain processing,which will be helpful for understanding the neural basis of sexual dimorphism in the facial attractiveness processing and the existing inconsistencies in previous studies. |
