Hemiface mobility and facial expression asymmetry

Thirty-seven right-handed college-aged males and females were assessed for facial asymmetry during emotional expression and for nonemotional hemiface mobility. Objective, subjective, and undirected measures of facial mobility were obtained, separately for the upper and lower face. While judges rated mobility of the lower face as left-sided, subjects declared themselves to be as facile on the right as on the left side of the face. When asked to move a side of the lower face, subjects moved the right side more frequently than the left. For the upper face, none of the measures of mobility were significantly left- or right-sided. Facial expression asymmetries (which were observed to be left-sided) were not significantly related to any measures of hemiface mobility.     

Oral asymmetries during verbal and non-verbal movements of the mouth

Asymmetries in the amplitude and velocity of oral movements were studied in 24 right-handed subjects as they produced either syllables or non-verbal movements of the mouth. Single-frame analysis of the videotaped mouth movements revealed that the right side of the mouth opened wider and faster than the left for both verbal and non-verbal movements. Moreover, the size of the right bias increased as a function of the complexity of required movements. In addition, movements embedded within a series showed a greater right bias than movements at the beginning of a series. On the whole, females exhibited larger asymmetries than males. These results provide support for the suggestion that the left hemisphere plays an important role in the control of complex motor behaviour.     

Emotional lateralisation in the second year of life: Evidence from oral asymmetries

Oral asymmetries for positive and negative emotional expressions were studied in 41 infants, ranging in age from 12 to 24 months. Single-frame analysis of videotapes of each infant's mouth showed that the left side of the mouth opened wider than the right side during negative emotional expressions but a mirror-image effect was not found for the expression of positive emotion. In addition, this directional bias strengthened with age. These results are interpreted as reflecting lateralisation of negative emotional production to the right hemisphere in infants as young as 12 months of age, a developmental enhancement of right hemisphere control of negative emotional expression that is evident by 24 months of age, and an absence of lateralisation for positive emotional expression in infants between 12 and 24 months of age.     

Emotional lateralisation in the second year of life: evidence from oral asymmetries

Oral asymmetries for positive and negative emotional expressions were studied in 41 infants, ranging in age from 12 to 24 months. Single-frame analysis of videotapes of each infant's mouth showed that the left side of the mouth opened wider than the right side during negative emotional expressions but a mirror-image effect was not found for the expression of positive emotion. In addition, this directional bias strengthened with age. These results are interpreted as reflecting lateralisation of negative emotional production to the right hemisphere in infants as young as 12 months of age, a developmental enhancement of right hemisphere control of negative emotional expression that is evident by 24 months of age, and an absence of lateralisation for positive emotional expression in infants between 12 and 24 months of age.     

Asymmetries in spontaneous facial expressions and their possible relation to hemispheric specialization

Unilateral expressive facial movements, as documented by field observation and by careful analysis of video recordings in the laboratory, occur more on the left side of the face than on the right side in right-handed people. In one of our studies, but not in others, a larger proportion of females than males showed this bias. Left-handers show no consistent asymmetries. It is suggested that facial expressions are mediated more by the right hemisphere than by the left.     

Differences in asymmetry of facial expression between left- and right-handed children

Ten left-handed children unselected for cerebral dominance and ten right-handed children, 8–10 yr old, posed for facial photographs while mimicking several emotional expressions. Left side and right side facial composites were prepared and shown to 30 raters. The majority of right-handed children were judged to be left facial dominant, while the left-handers were judged to be mainly indeterminate and right facial dominant. These findings indicate a difference in hemifacial emotional expression between left- and right-handed children.     

Lateralized Asymmetries in Self-Perception

Thirty right-handed males and females, displaying happy and sad expressions, compared left-left and right-right composites of his/her own face. For each pair of composites, depicting one emotional state, subjects chose that composite which (a) looked most like themselves and (b) depicted the more intense emotion. The results for females failed to support the contention that the right hemisphere specializes in the perception of negative affect whereas the left hemisphere is prominent for positive states. Finally, asymmetries were more pronounced in females rather than males.     

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.     

Asymmetry of facial expression in spontaneous emotion

The observation that emotional expressions are more intense on the left side of the face is consistent with other evidence of the importance of the right hemisphere in emotional communication. However, the question has been raised whether it is truly spontaneous emotional expressions or only posed facial displays that show a left-sided asymmetry. We surreptitiously examined facial asymmetry during spontaneous emotional expressions as subjects remembered happy or sad experiences. These were contrasted with the subjects' posed expressions of happy or sad emotions. Both of these procedures resulted in more intense expressions on the left side of the face. The left-sided advantage was stronger during the spontaneous than the posed displays, and was observed for both happy and sad emotions.     

The expression and perception of facial emotion in brain-damaged patients

This study examined the expression and perception of facial emotion in patients with unilateral cerebrovascular pathology. Subjects were 12 right brain-damaged (RBD), 15 left brain-damaged (LBD) aphasic, and 16 normal control (NC) right-handed males. Expressions were elicited during posed and spontaneous conditions. Both positive and negative emotions were studied. RBDs were significantly impaired, relative to LBDs and NCs, in expressing and perceiving facial emotion. There were no group differences as a function of condition, but there were differences as a function of emotional valence. Qualitative performance differences also were observed. There was no evidence that the ability to produce a particular emotion was related to the ability to identify the same emotion. Overall, these findings support the notion that the right cerebral hemisphere is dominant for expressing and perceiving facial emotion.     

Asymmetries of the central sulcus in young adults: Effects of gender,age and sulcal pattern

In this study, we clarified the gender and age-related asymmetries of the central sulcus (CS) in early adulthood using a parametric ribbon method. The CS was reconstructed and parameterized automatically from 3D MR images of 112 healthy right-handed subjects. The 3D anatomic morphology of the CS was presented using 5 sulcal parameters, including sulcal depth position-based profile (DPP), average depth (AD), average width (AW), top length (TL) and bottom length (BL). Asymmetry differences in DPPs were found in the medial and lateral part of the CS. In addition, significant gender differences were observed in the medial and middle parts of the right CS DPPs but scattered in the left side. We found leftward asymmetries of TL in males, but rightward asymmetries of AW in females. Males had a greater AW than females in the right hemisphere. Moreover, the females had bilateral longer TL and a longer left BL than did males. We also found significant age-related reductions in bilateral TL and increases in bilateral AW, with males presenting more obvious age-related change than females. There were sexual differences of the CS patterns, in which Type b was the most dominant sulcal pattern in males, whereas Type a was dominant in females. Three-way ANOVA revealed sexual and asymmetry changes of TL and BL among different CS patterns. Our findings indicate that the lateralization performances of the CS manifest as sexually and regionally different. In addition, it is suggested that males may undergo a faster progress of aging compared to females.     

The influence of gender, handedness and head-turn on auditory asymmetries

Subjects performed dichotic tasks with their heads turned 90° to the left, 90° to the right, and straight ahead. In Experiment 1 the stimuli were digits and the subjects varied in both sex and handedness. Right-handedness males showed a significant right-ear advantage under the head-right and head-straight conditions, while left-handed males and both right- and left-handed females failed to show any consistent ear asymmetries. In Experiment 2 the stimuli were melodies and the subjects were all right-handed. Head-turn had no significant influence on the results, and only the males showed a significant left-ear advantage. Overall, the results confirm previous findings that sex and handedness may influence auditory asymmetries, but fail to reveal systematic effects of head turn.     

Asymmetries in mouth opening during word generation in male stuttering and non-stuttering participants

We examined lateral asymmetries in mouth opening in right-handed male stuttering (N = 11) and non-stuttering (N = 14) participants. Lateral asymmetries in mouth opening were video-recorded and analysed in participants while they generated words beginning with the bilabial phones /b, p, m/. Non-stuttering participants showed an expected preference for right mouth opening during the task, whereas a group of stuttering participants who were matched for sex and age produced a left or bilateral pattern of mouth opening. Analysis of variance revealed the difference between the groups to be significant (p < .001). However, there was more variability in the lateral mouth asymmetries in the stuttering participants. We interpret this finding as adding some support for the hypothesis that aberrant hemispheric control for speech is involved in stuttering. Asymmetric mouth openings appear to have no direct linguistic function, and we discuss the possible implications of the phenomenon for models of speech planning and programming.     

Asymmetries in mouth opening during word generation in male stuttering and non-stuttering participants

We examined lateral asymmetries in mouth opening in right-handed male stuttering (N = 11) and non-stuttering (N = 14) participants. Lateral asymmetries in mouth opening were video-recorded and analysed in participants while they generated words beginning with the bilabial phones /b, p, m/. Non-stuttering participants showed an expected preference for right mouth opening during the task, whereas a group of stuttering participants who were matched for sex and age produced a left or bilateral pattern of mouth opening. Analysis of variance revealed the difference between the groups to be significant (p < .001). However, there was more variability in the lateral mouth asymmetries in the stuttering participants. We interpret this finding as adding some support for the hypothesis that aberrant hemispheric control for speech is involved in stuttering. Asymmetric mouth openings appear to have no direct linguistic function, and we discuss the possible implications of the phenomenon for models of speech planning and programming.     

Asymmetry of the face at rest: size, area and emotional expression

In a sample of 53 right-handed, young adult males, asymmetry was examined in the size of 11 facial regions, in total area, and in emotional expression of the face at rest. In the complete sample no evidence was obtained of consistent asymmetry in size of facial regions, in facial area, or in emotional expression. There was, however, an interaction between family history of sinistrality and sighting dominance in facial asymmetry for the pleasantness/unpleasantness of facial expression. The findings suggest that previously established asymmetries in phasic emotional displays are not an outcome of expressive or morphological asymmetries of the face at rest.     

Digitizing the moving face during dynamic displays of emotion

Humans typically decode facial signals during dynamic interactions in which the face moves. In this study, we digitized real time video signals in order to examine movement asymmetries across the face during emotional and nonemotional expressions. Forty dextral males were tested. For each expression, a 400 ms video segment was analyzed for changes in signal value (pixel intensity) over consecutive frames. The upper and lower face regions were examined separately due to differences in the cortical enervation of facial muscles in the upper (bilateral) vs lower face (contralateral). Results revealed distinctly different movement asymmetries over the lower and upper hemiface. In the upper face, more movement occurred over the right side for most facial expressions, regardless of emotionality. The latter finding questions the assumption that muscles of the upper face are symmetrical and/or bilaterally enervated in a symmetrical manner. In the lower face, negative expressions linked to fight-flight emotions (i.e. fear, anger) were associated with greater left sided movement, whereas happiness tended to be associated with more right sided movement. No consistent pattern of movement asymmetry occurred for nonemotional expressions. Although the valence-related movement asymmetries in the lower face are consistent with neuropsychological models of emotional expressivity, it remains unclear whether they reflect activation or inhibitory hemispheric mechanisms. Taken together, these data suggest that multiple factors may contribute to expressive movement asymmetries of the face.     

Hemispheric specialization and the perception of emotion: Evidence from right-handers and from inverted and non-inverted left-handers

Right-handers and inverted and non-inverted left-handers viewed emotional expressions in one hemifield and, simultaneously, a neutral expression of the same poser in the other hemifield. Subjects were required to identify the side containing the affective face. Happy faces with open (i.e. salient) and closed mouth smiles and sad faces were used as stimuli. For right-handers and inverters reaction time was faster to right hemifield presentations for happy faces and to left hemifield presentations for sad faces. Non-inverters showed the reverse pattern. The saliency of the happy expressions had no effect on the magnitude and direction of asymmetry for any group. The data support the hypothesis of differential hemispheric specialization for positive and negative emotion and demonstrate opposite patterns of asymmetry in affect perception for inverted and non-inverted left-handers.     

Topographic brain mapping of emotion-related hemisphere asymmetries.

The study used topographic brain mapping of visual evoked potentials to investigate emotion-related hemisphere asymmetries. The stimulus material consisted of color photographs of human faces, grouped into two emotion-related categories: normal faces (neutral stimuli) and faces deformed by dermatological diseases (emotional stimuli). The pictures were presented tachistoscopically to 20 adult right-handed subjects. Brain activity was recorded by 30 EEG electrodes with linked ears as reference. The waveforms were averaged separately with respect to each of the two stimulus conditions. Statistical analysis by means of significance probability mapping revealed significant differences between stimulus conditions for two periods of time, indicating right hemisphere superiority in emotion-related processing. The results are discussed in terms of a 2-stage-model of emotional processing in the cerebral hemispheres.     

Interhemispheric asymmetry of the human motor cortex related to handedness and gender

Most people are right-handed, preferring the right hand for skilled as well as unskilled activities, but a notable proportion are mixed-handed, preferring to use the right hand for some actions and the left hand for others. Assuming a structural/functional correlation in the motor system we tested whether asymmetries in hand performance in consistent right and left handers as well as in mixed handers are associated with anatomical asymmetries in the motor cortex. In vivo MR morphometry was used for analyzing interhemispheric asymmetry in the depth of the central sulcus in the region of cortical hand representation of 103 healthy subjects. Subjects were tested both for hand preference and hand performance. As expected, left-right differences in hand performance differed significantly between consistent right, consistent left and mixed handers and were independent on gender. Male consistent right handers showed a significant deeper central sulcus on the left hemisphere than on the right. Anatomical asymmetries decreased significantly from male consistent right over mixed to consistent left handers. Sixty two per cent of consistent left handers revealed a deeper central sulcus on the right than on the left hemisphere, but for the group as a whole this rightward asymmetry was not significant. No interhemispheric asymmetry was found in females. Thus, anatomical asymmetry was associated with handedness only in males, but not in females, suggesting sex differences in the cortical organization of hand movements.     

Right-, left-dominance and ambidexterity in grasp reflex in human newborn: importance of left brain in cerebral lateralization.

The grasp reflex was studied in human newborn without familial sinistrality. Of 60 females, 26 (43.3%) were right-handed and 34 (56.7%) ambidextrous. Of 62 males, 20 (32.3%) were right-handed, 39 (62.9%) ambidextrous, and 3 (4.8%) left-handed. There was a nonsignificant preponderance of right-dominance in females and a significant preponderance of nonright-handedness in males. In right-handers, the mean right minus left (R-L) grasp-reflex showed a positive linear correlation with the grasp-reflex from the right and left hands, with a higher correlation for the right hand. In ambidexters, the R-L grasp reflex did not show any significant correlation with the grasp reflex from the right and left hands. The mean grasp-reflex from right and left were found to be significantly smaller in ambidextrous males and females then right-handed males and females, with a much higher significance for the right hand. It was concluded that females tended to have a more pronounced reflex lateralization than males. The results also indicated that the left brain may be more important than the right brain for the development of a spinocerebral motor lateralization in humans.