Asymmetry in positive and negative facial expressions: Sex differences

Facial asymmetry (facedness) during posed emotional expression was correlated with measures of lateral dominance in 48 right- and left-handed normal adults. Positive and negative aspects of expression were refined by factor analysis. The finding for males that facedness for pleasant expressions was positively correlated with handedness and footedness may reflect linguistic factors. Discussion covers the nature of and laterality for positive/negative, communicative/reactive and approach/withdrawal dimensions of emotional expression.     

Facedness and emotion related to lateral dominance,sex and expression type

Facial asymmetry or “facedness” was reliably rated for nine different videotaped facial expressions of emotion, produced by 51 adults, and was significantly left-sided. This finding was related to right hemisphere dominance for emotion and for facial movement. No overall differences occurred for expression type or sex and handedness of subjects, but there were interactions.     

The role of structural facial asymmetry in asymmetry of peak facial expressions

Asymmetric facial expression is generally attributed to asymmetry in movement, but structural asymmetry in the face may also affect asymmetry of expression. Asymmetry in posed expressions was measured using image-based approaches in digitised sequences of facial expression in 55 individuals, N=16 men, N=39 women. Structural asymmetry (at neutral expression) was higher in men than women and accounted for .54, .62, and .66 of the variance in asymmetry at peak expression for joy, anger, and disgust expressions, respectively. Movement asymmetry (measured by change in pixel values over time) was found, but was unrelated to peak asymmetry in joy or anger expressions over the whole face and in facial subregions relevant to the expression. Movement asymmetry was negatively related to peak asymmetry in disgust expressions. Sidedness of movement asymmetry (defined as the ratio of summed movement on the left to movement on the right) was consistent across emotions within individuals. Sidedness was found only for joy expressions, which had significantly more movement on the left. The significant role of structural asymmetry in asymmetry of emotion expression and the exploration of facial expression asymmetry have important implications for evolutionary interpretations of facial signalling and facial expressions in general.     

The role of structural facial asymmetry in asymmetry of peak facial expressions

Asymmetric facial expression is generally attributed to asymmetry in movement, but structural asymmetry in the face may also affect asymmetry of expression. Asymmetry in posed expressions was measured using image-based approaches in digitised sequences of facial expression in 55 individuals, N=16 men, N=39 women. Structural asymmetry (at neutral expression) was higher in men than women and accounted for .54, .62, and .66 of the variance in asymmetry at peak expression for joy, anger, and disgust expressions, respectively. Movement asymmetry (measured by change in pixel values over time) was found, but was unrelated to peak asymmetry in joy or anger expressions over the whole face and in facial subregions relevant to the expression. Movement asymmetry was negatively related to peak asymmetry in disgust expressions. Sidedness of movement asymmetry (defined as the ratio of summed movement on the left to movement on the right) was consistent across emotions within individuals. Sidedness was found only for joy expressions, which had significantly more movement on the left. The significant role of structural asymmetry in asymmetry of emotion expression and the exploration of facial expression asymmetry have important implications for evolutionary interpretations of facial signalling and facial expressions in general.     

Lateral Eye Movement and Handedness as Measures of Functional Brain Asymmetry in Learning Disability

Evidence is presented which suggests that learning disability is related to lateral asymmetry. Significant differences were found in lateral eye movement and handedness between a learning disabled group and a control group of normal learners. Left lateral eye movement and right handedness was the predominant pattern exhibited in learning disability. These results support Day's notion that left lateral eye movement is associated with educational difficulties. They also provide evidence concerning Orton's hypothesis that mixed cerebral dominance characterizes the learning disabled.     

Orientation of the stethoscope around the neck: a random phenomenon or an indicator of cerebral lateralisation? Cross-sectional survey

This study aimed to determine whether the orientation of the stethoscope when placed around the neck by physicians is a random occurrence or if this represents a lateral preference. A cross-sectional questionnaire survey was conducted, recruiting 186 medical doctors of all grades from the University Hospital of Wales, Cardiff. Stethoscope orientation preference, and seven other measures of lateral preference (handedness, footedness, eyedness, earedness, hand clasping, arm folding, and leg crossing), were assessed. The percentage of right-type, left-type, and indifferent-type orientation for each of the eight lateral preferences was determined, and 60%, 35%, and 5% of participants demonstrated right, left, and indifferent stethoscope orientation types, respectively. Stethoscope orientation preference correlated with handedness, footedness, earedness, and hand-clasping, but not with eyedness, arm-folding, or leg-crossing. Stethoscope orientation preference is not a chance phenomenon and may be an expression of cerebral dominance.     

Hemispheric and facial asymmetry: gender differences

Facial asymmetry (facedness) of female and male college students was investigated. Comparisons of facedness were made between 45 female and 45 male Dartmouth undergraduates. Facedness was defined in terms of the relative sizes (in square centimetres) of the two hemifaces. Data were derived from measurements of two-dimensional frontal photographs of the subjects. Reliable differences in facedness were found between the two groups. The females on average were found to be right faced, the males left faced. This difference was interpreted in terms of the contralateral control (below the eyes) of the two sides of the face by the two hemispheres, and the known differences in cognitive processing by the two hemispheres (left hemisphere-verbal; right hemisphere-visuospatial) in females and males. The observed difference in facial asymmetry between the two sexes is attributed to differential muscular development of the two sides of the face as related to the factors just noted. Suggestions are made for further research on facedness, particularly in relation to different age groups.     

Facial asymmetry while posing positive and negative emotions: support for the right hemisphere hypothesis

The purpose of this report was to examine facial asymmetry during the expression of positive and negative emotions. In addition, methodological factors in the study of facial asymmetry were considered. Subjects were 16 neurologically-healthy right-handed adult males, videotaped while posing eight facial expressions (positive and negative) under two conditions (verbal command and visual imitation). Separate asymmetry ratings of the two sides of the face were made by judges viewing normal or mirror-reversed versions of the videotape. There were no effects of valence, condition, or videotape orientation on the asymmetry ratings, and, in general, expressions were produced significantly more intensely on the left than the right side of the face. This finding is consistent with the hypothesis that the right cerebral hemisphere is dominant for the expression of facial emotion of both valences.     

The Development of Facedness

Thirty-two children of both sexes, ranging in age from 6 to 13 years, were photographed while posing or imitating happiness, sadness or surprise. Full-face photographs which were considered by independent judges to express the intended emotions were submitted to a split-face recombination procedure that created two composites from each face, one from the left side and the other from the right. Independent observers found the left composites to be more expressive than the right m the older group (age 12–13), but not in the younger groups, who evinced no left-right asymmetries. This finding applied similarly to the three emotions, and did not depend on an age-related change in the capacity for emotional expression.Further, left-right asymmetries in facial expression, where present, did not correlate with difference in size between the two halves of the face, and were found for both the upper and lower parts of the face. It is concluded that the advantage of the left hemiface for emotional expression, which is typical of adults, is the result of growth and development. While this facial asymmetry is likely to depend on an hemispheric asymmetry favoring the right side of the brain for the volitional control of the facial musculature, the neural mechanisms of the phenomenon of facedness are still largely obscure.     

Subject Variables and Cerebral Organization for Language

The present study investigated the usefulness of a variety of subject variables that have been proposed as having predictive value for determining cerebral organization for language. To accomplish this, a total of 373 subjects (117 left-handers and 256 right-handers) were given 240 trials of a consonant-vowel dichotic listening task to assess direction and degree of language lateralization. Each subject was also classified on the basis of eight subject variables (handedness, strength of handedness, familial sinistrality, writing hand posture, sex, sighting dominance, preferred footedness, and overall laterality). The results of the study indicated that left hemisphere language processing is very pervasive and that most of the subject variables examined were not very useful predictors of language lateralization. In addition, surprisingly, footedness and not handedness was the single best predictor of cerebral organization for language.     

Lateral preferences and performance on non-verbal laterality tests in a normal population

The goal of the present study was to determine if, in a normal population, handedness, footedness, eyedness, earedness and overall congruency across lateral preferences were predictive of perceptual asymmetry on non-verbal tasks. In Experiment 1, subjects had to decide whether a laterally presented facial expression matched a previously presented target. In Experiment 2, subjects had to determine whether the tone of voice heard on dichotic and binaural presentations was the same or different. Eye preference was the most successful variable in predicting both visual field and ear advantages. Knowledge of a person's eye preference however, did not allow for a very accurate prediction of perceptual asymmetry. Nonetheless, the findings suggest that eye preference should be taken into account in future non-verbal laterality studies.     

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.     

Aphasia in left-handers: lesion site, lesion side, and hemispheric asymmetries on CT

Language in left-handed aphasics with left (n = 27) or right (n = 4) hemisphere lesion was examined. Left occipital CT asymmetry was the most common asymmetry and could not be used to predict handedness or which hemisphere, if damaged, would produce aphasia. When left hemisphere lesion sites were matched between eight left-handed and eight right-handed aphasics, there were no significant group differences on language measures. Two nonfluent cases with good comprehension and large right frontal, parietal, and temporal lesions appeared to have "Broca's area" in the right hemisphere, but "Wernicke's area" in the left. Results suggest separate hemispheric loci for handedness, speech output, and/or comprehension dominance in some left-handers.     

The measurement of foot preference

Foot preference has been given only superficial attention in studies of hemispheric lateralization, although it has potential utility for predicting hemispheric dominance. This paper reports the development of a reliable (alpha = 0.89) 11-item behavioral inventory of foot preference. Since footedness and handedness are only partially related, both must be measured reliably to identify individuals who have a consistent right or left side preference. It has yet to be determined whether footedness or handedness has the stronger relationship to other aspects of cerebral lateralization and whether both measures together predict lateralization better than one of them alone.     

Left-handers' smiles: asymmetries in the projection of a posed expression

Asymmetries in the expression of a posed smile and in a relaxed facial expression were observed in 24 left-handers. Neither writing position nor familial sinistrality predicted the variance of the results. Left-handers were found to smile more with their left than right side of face; an asymmetry which had previously been observed in right-handers. If anything, left-handers' smiles were more asymmetric, though in the same direction, than right-handers. When relaxed, however, the left-handers' face was judged more unhappy on its right than left side--a reversal of the direction of asymmetry previously noted in right-handers' relaxed expressions. No single neurological or psychological theory accounts for these results; it is suggested that hand preference may exert a myotonic effect which is reflected in judgements of relaxed facial expressions.     

Footedness is a Better Predictor of Language Lateralisation than Handedness

A tremendous amount of experimental work has attempted to identify a reliable behavioural predictor of language lateralisation. Preferred handedness has probably received the most attention, but there are some recent reports that preferred footedness may serve as a more reliable predictor. The present study sought to test this claim by selectively recruiting 32 participants such that the factors of handedness, footedness, and gender were completely crossed. Language lateralisation was assessed with the Fused Dichotic Words Test (FDWT), and lateral preference for both handedness and footedness was assessed using selfreport questionnaires. Ear advantage on the dichotic task varied significantly with preferred foot (P <.001) but not with preferred hand (P = .196). This result is problematic for evolutionary theories of cerebral lateralisation that claim lefthemispheric language is related to fine manual motor skill and sequencing. Language lateralisation may be more closely related to asymmetrical control of whole-body finely sequenced movements.     

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.     

Right brain, left brain; left face, right face: hemisphericity and the expression of facial emotion

Research on the asymmetry of facial expressions is reviewed in terms of neuroanatomy, qualitative and quantitative measures of asymmetrical expression, method of expression elicitation (spontaneous, posed, imagery-based), type of expression (happy, sad, etc.), and expression rating procedures. Neuroanatomical evidence indicated that contralateral control of facial musculature exists only for the lower face and that different motor pathways are responsible for spontaneous versus posed expressions. Empirical research on the differential assignment of qualitative trait attributes to facial regions was judged to be meagre and data on quantitative differences in the asymmetry of facial expressions was inconclusive because of the wide variability in methodology across past investigations. Specific suggestions for future investigations in this area are offered and alternative conceptualizations of hemisphericity and facial asymmetry proposed.     

Hemispheric differences in recognition of facial expressions: a VHF-study of negative, positive, and neutral emotions

The present study was concerned with a tachistoscopic investigation of asymmetry of recognition of different facial emotional expressions. Twenty-eight subjects had nine different drawings of facial expressions (either positive, negative, or neutral in emotional content) presented either to the left or right visual half-field. Recognition of the correct face was made for each stimulus-presentation. The results showed overall better recognition for presentations in the left half-field (LVF) (i.e., right hemisphere) compared to right half-field (RVF) (i.e., left hemisphere) presentations. Furthermore, while all three emotional categories were recognized about equally well in the right half-field, positive emotional expressions were significantly better than the neutral and negative categories when presented to the left half-field. The results are discussed in relation to previous findings of cerebral asymmetry in processing of emotional facial expressions.     

Footedness is a better predictor of language lateralisation than handedness

A tremendous amount of experimental work has attempted to identify a reliable behavioural predictor of language lateralisation. Preferred handedness has probably received the most attention, but there are some recent reports that preferred footedness may serve as a more reliable predictor. The present study sought to test this claim by selectively recruiting 32 participants such that the factors of handedness, footedness, and gender were completely crossed. Language lateralisation was assessed with the Fused Dichotic Words Test (FDWT), and lateral preference for both handedness and footedness was assessed using self-report questionnaires. Ear advantage on the dichotic task varied significantly with preferred foot ( P <.001) but not with preferred hand ( P = .196). This result is problematic for evolutionary theories of cerebral lateralisation that claim left-hemispheric language is related to fine manual motor skill and sequencing. Language lateralisation may be more closely related to asymmetrical control of whole-body finely sequenced movements.