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.     

Lateralisation of perceptual processing of pro- and anti-social emotions displayed in chimeric faces

Previous studies using a restricted range of split field chimeric faces suggest that the processing of facial emotional expressions is a highly lateralised phenomenon. Two theories have emerged with regard to the role the two cerebral hemispheres play in this processing. The "right hemisphere" hypothesis (e.g. Borod, Koff, Lorch, & Nicholas, 1988) suggests that the right hemisphere plays a prominent role in the processing of both positive and negative facial expressions. In contrast, the "valence hypothesis" (e.g. Reuter-Lorenz & Davidson, 1981) proposes that, while the right hemisphere plays the major role in processing negative emotions, the left hemisphere has a special role for positive emotions. Using all six of the human "universal facial expressions" (Ekman &Friesen, 1971) we present evidence that, superimposed onto a left visual field advantage (right hemisphere specialisation) for emotional processing, there is a "left shift" (right visual field advantage) for pro- as opposed to anti-social expression. We propose that facial expressions that are likely to be related to approach for communicative purposes initiate a greater degree of left hemisphere involvement. As a consequence, we suggest that for future laterality studies, the six universal emotional expressions should be reconsidered using a pro- to anti-social dimension rather than positive and negative groupings.     

Lateralisation of perceptual processing of pro- and anti-social emotions displayed in chimeric faces

Previous studies using a restricted range of split field chimeric faces suggest that the processing of facial emotional expressions is a highly lateralised phenomenon. Two theories have emerged with regard to the role the two cerebral hemispheres play in this processing. The "right hemisphere" hypothesis (e.g. Borod, Koff, Lorch, & Nicholas, 1988) suggests that the right hemisphere plays a prominent role in the processing of both positive and negative facial expressions. In contrast, the "valence hypothesis" (e.g. Reuter-Lorenz & Davidson, 1981) proposes that, while the right hemisphere plays the major role in processing negative emotions, the left hemisphere has a special role for positive emotions. Using all six of the human "universal facial expressions" (Ekman &Friesen, 1971) we present evidence that, superimposed onto a left visual field advantage (right hemisphere specialisation) for emotional processing, there is a "left shift" (right visual field advantage) for pro- as opposed to anti-social expression. We propose that facial expressions that are likely to be related to approach for communicative purposes initiate a greater degree of left hemisphere involvement. As a consequence, we suggest that for future laterality studies, the six universal emotional expressions should be reconsidered using a pro- to anti-social dimension rather than positive and negative groupings.     

Patterns of brain asymmetry in the perception of positive and negative facial expressions

The divided visual field technique was used to investigate the pattern of brain asymmetry in the perception of positive/approach and negative/withdrawal facial expressions. A total of 80 undergraduate students (65 female, 15 male) were distributed in five experimental groups in order to investigate separately the perception of expressions of happiness, surprise, fear, sadness, and the neutral face. In each trial a target and a distractor expression were presented simultaneously in a computer screen for 150 ms and participants had to determine the side (left or right) on which the target expression was presented. Results indicated that expressions of happiness and fear were identified faster when presented in the left visual field, suggesting an advantage of the right hemisphere in the perception of these expressions. Fewer judgement errors and faster reaction times were also observed for the matching condition in which emotional faces were presented in the left visual field and neutral faces in the right visual field. Other results indicated that positive expressions (happiness and surprise) were perceived faster and more accurately than negative ones (sadness and fear). Main results tend to support the right hemisphere hypothesis, which predicts a better performance of the right hemisphere to perceive emotions, as opposed to the approach–withdrawal hypothesis.     

Patterns of brain asymmetry in the perception of positive and negative facial expressions

The divided visual field technique was used to investigate the pattern of brain asymmetry in the perception of positive/approach and negative/withdrawal facial expressions. A total of 80 undergraduate students (65 female, 15 male) were distributed in five experimental groups in order to investigate separately the perception of expressions of happiness, surprise, fear, sadness, and the neutral face. In each trial a target and a distractor expression were presented simultaneously in a computer screen for 150 ms and participants had to determine the side (left or right) on which the target expression was presented. Results indicated that expressions of happiness and fear were identified faster when presented in the left visual field, suggesting an advantage of the right hemisphere in the perception of these expressions. Fewer judgement errors and faster reaction times were also observed for the matching condition in which emotional faces were presented in the left visual field and neutral faces in the right visual field. Other results indicated that positive expressions (happiness and surprise) were perceived faster and more accurately than negative ones (sadness and fear). Main results tend to support the right hemisphere hypothesis, which predicts a better performance of the right hemisphere to perceive emotions, as opposed to the approach-withdrawal hypothesis.     

Hemisphere Differences in Perceiving Positive and Negative Emotions

Two experiments tested the hypothesis that positive emotions are processed primarily by the left hemisphere and negative emotions by the right hemisphere. In both experiments, facial expressions of positive and negative emotions were briefly presented to the left and right visual fields of normal dextral subjects. Experiment 1 investigated hemisphere differences in accuracy for naming the emotions, and Experiment 2 examined hemisphere differences in judging the intensity of the emotional expressions. Neither experiment found support for the hypothesized relationship. It was concluded that differential hemisphere involvement in processing positive and negative emotions, as suggested by previous studies, may occur, but only for the production, and not the perception of emotional expressions.     

Examining the relationship between lateralisation for processing emotional faces,depression, and sex

It is now relatively well established that the right hemisphere is specialised for processing facial emotion; however, there is variability in this pattern of lateralisation. One factor that has been examined is atypical lateralisation in individuals diagnosed with clinical psychological conditions. To date the evidence regarding the neuropsychological processing of emotional stimuli in individuals with depression is contradictory. In this study 160 participants completed the Beck Depression Inventory and the chimeric faces test, a test of lateralisation for the processing of facial expressions of each of the six basic emotions. A negative relationship between depression and lateralisation was found for females only, showing that women with higher depression scores tend to be less strongly lateralised to the right hemisphere, or even lateralised to the left hemisphere, for processing facial emotion. The strength of this relationship also varied across the different emotions with the clearest results for the processing of anger, disgust, and fear. There were no significant findings for males. The possible reasons for there being a sex difference in our findings and an attempt to reconcile the disparate findings within this area of research are discussed.     

Development of cerebral lateralisation for recognition of emotions in chimeric faces in children aged 5 to 11

In contrast to research into the development of language laterality, there has been relatively little research into the development of lateralisation of emotional processing. If language lateralisation begins in childhood and is complete by puberty (Lenneberg, 1967) it seems reasonable that the lateralisation of the perception of emotions might also occur during this period. In this study a split field chimeric faces test using the six universal facial expressions proposed by Ekman and Friesen (1971), an emotion in the eyes test, and a situational cartoon test were administered to three groups of children aged 5/6, 7/8, and 10/11. No overall hemispace advantage was seen for the 5/6-year-old group, but by the age of 10/11 a clear left hemispace advantage (right hemisphere) was found for all six emotions. Such a pattern is comparable to a previous study that made use of adults on this task (Workman, Peters, & Taylor, 2000b). Moreover, a significant positive correlation between a child's ability to recognise emotions in cartoon situations and their left hemispatial advantage score was uncovered. Finally, a significant positive correlation between a child's ability to recognise emotions in the eyes of others and their left hemispatial advantage score was also uncovered. These findings are taken as evidence that there may be a relationship between the development of emotional processing in the right hemisphere and a child's emerging ability to perceive or attend to the emotional states of others. Results are discussed in relation to the child's development of a theory of mind.     

Lateralisation effect in comprehension of emotional facial expression: A comparison between EEG alpha band power and behavioural inhibition (BIS) and activation (BAS) systems

Asymmetry in comprehension of facial expression of emotions was explored in the present study by analysing alpha band variation within the right and left cortical sides. Second, the behavioural activation system (BAS) and behavioural inhibition system (BIS) were considered as an explicative factor to verify the effect of a motivational/emotional variable on alpha activity. A total of 19 participants looked at an ample range of facial expressions of emotions (anger, fear, surprise, disgust, happiness, sadness, and neutral) in random order. The results demonstrated that anterior frontal sites were more active than central and parietal sites in response to facial stimuli. Moreover, right and left side responses varied as a function of emotional types, with an increased right frontal activity for negative, aversive emotions vs an increased left response for positive emotion. Finally, whereas higher BIS participants generated more right hemisphere activation for some negative emotions (such as fear, anger, surprise, and disgust), BAS participants were more responsive to positive emotion (happiness) within the left hemisphere. Motivational significance of facial expressions was considered to elucidate cortical differences in participants' responses to emotional types.     

Right-sided facial asymmetry in infant emotional expression

In normal adults, emotional expressions tend to be more intense on the left side of the face, while in preschool-age children, no significant bias in facial asymmetry has been found. We examined facial asymmetries during smiling and distress in 59 infants studied longitudinally at 6.5, 10 and 13.5 months of age. In these infants, asymmetric expressions showed a bias toward greater intensity on the right side of the face. The study of infant facial expression may provide clues to the maturation of the cortical control of emotional responses.     

Perception of emotions from faces and voices following unilateral brain damage

The importance of the right hemisphere in emotion perception in general has been well documented but its precise role is disputed. We compared the performance of 30 right hemisphere damaged (RHD) patients, 30 left hemisphere damaged (LHD) patients, and 50 healthy controls on both facial and vocal affect perception tasks of specific emotions. Brain damaged subjects had a single episode cerebrovascular accident localised to one hemisphere. The results showed that right hemisphere patients were markedly impaired relative to left hemisphere and healthy controls on test performance: labelling and recognition of facial expressions and recognition of emotions conveyed by prosody. This pertained at the level of individual basic emotions, positive versus negative, and emotional expressions in general. The impairment remained highly significant despite covarying for the group's poorer accuracy on a neutral facial perception test and identification of neutral vocal expressions. The LHD group were only impaired relative to controls on facial emotion tasks when their performance was summed over all the emotion categories and before age and other cognitive factors were taken into account. However, on the prosody test the LHD patients showed significant impairment, performing mid-way between the right hemisphere patients and healthy comparison group. Recognition of positive emotional expressions was better than negative in all subjects, and was not relatively poorer in the LHD patients. Recognition of individual emotions in one modality correlated weakly with recognition in another, in all three groups. These data confirm the primacy of the right hemisphere in processing all emotional expressions across modalities--both positive and negative--but suggest that left hemisphere emotion processing is modality specific. It is possible that the left hemisphere has a particular role in the perception of emotion conveyed through meaningful speech.     

Linking children's neuropsychological processing of emotion with their knowledge of emotion expression regulation

Understanding of emotions has been shown to develop between the ages of 4 and 10 years; however, individual differences exist in this development. While previous research has typically examined these differences in terms of developmental and/or social factors, little research has considered the possible impact of neuropsychological development on the behavioural understanding of emotions. Emotion processing tends to be lateralised to the right hemisphere of the brain in adults, yet this pattern is not as evident in children until around the age of 10 years. In this study 136 children between 5 and 10 years were given both behavioural and neuropsychological tests of emotion processing. The behavioural task examined expression regulation knowledge (ERK) for prosocial and self-presentational hypothetical interactions. The chimeric faces test was given as a measure of lateralisation for processing positive facial emotion. An interaction between age and lateralisation for emotion processing was predictive of children's ERK for only the self-presentational interactions. The relationships between children's ERK and lateralisation for emotion processing changes across the three age groups, emerging as a positive relationship in the 10-year-olds. The 10-years-olds who were more lateralised to the right hemisphere for emotion processing tended to show greater understanding of the need for regulating negative emotions during interactions that would have a self-presentational motivation. This finding suggests an association between the behavioural and neuropsychological development of emotion processing.     

Asymmetry in facial expression of emotions by chimpanzees

Asymmetries in human facial expressions have long been documented and traditionally interpreted as evidence of brain laterality in emotional behavior. Recent findings in nonhuman primates suggest that this hemispheric specialization for emotional behavior may have precursors in primate evolution. In this study, we present the first data collected on our closest living relative, the chimpanzee. Objective measures (hemimouth length and area) and subjective measures (human judgements of chimeric stimuli) indicate that chimpanzees' facial expressions are asymmetric, with a greater involvement of the left side of the face in the production of emotional responses. No effect of expression type (positive versus negative) on facial asymmetry was found. Thus, chimpanzees, like humans and some other nonhuman primates, show a right hemisphere specialization for facial expression of emotions.     

Dopaminergic lateralisation in the forebrain: relations to behavioural asymmetries and anxiety in male Wistar rats

Neurochemical lateralisation has been demonstrated in dopaminergic systems in the rat brain, and it has been suggested that such lateralisation might contribute to asymmetric and emotional behaviour. Here, we investigated dopaminergic brain lateralisation in relation to spontaneous and drug-induced behavioural asymmetries, and to emotional behaviour in a sample of 24 male Wistar rats. Asymmetric behaviour was measured in the open field in the undrugged state and after a systemic challenge with the muscarinic receptor antagonist scopolamine (0.5 mg/kg). Emotional behaviour was measured in the elevated plus-maze. Dopaminergic lateralisation was assessed by means of a post-mortem analysis of tissue dopamine (DA) and dihydroxyphenyl acetic acid (DOPAC) content. We found higher DOPAC/DA ratios in the neostriatum, ventral striatum, frontal cortex and amygdala of the right hemisphere. In the open field, the complete sample of rats did not show a left/right asymmetry in spontaneous behaviour, whereas systemic scopolamine induced a left-sided preference in thigmotactic scanning. A correlational analysis yielded individual relationships between behaviour and post-mortem neurochemistry, since lateralisation of DOPAC/DA ratios in favour of the right ventral striatum was related to right-side thigmotaxis. Furthermore, a right dopaminergic lateralisation in the frontal cortex was associated with lower anxiety. The study indicates that asymmetries in ventral striatal dopamine might contribute to side preferences in thigmotactic scanning while frontal dopaminergic lateralisation might influence emotional processing.     

Linking children's neuropsychological processing of emotion with their knowledge of emotion expression regulation

Understanding of emotions has been shown to develop between the ages of 4 and 10 years; however, individual differences exist in this development. While previous research has typically examined these differences in terms of developmental and/or social factors, little research has considered the possible impact of neuropsychological development on the behavioural understanding of emotions. Emotion processing tends to be lateralised to the right hemisphere of the brain in adults, yet this pattern is not as evident in children until around the age of 10 years. In this study 136 children between 5 and 10 years were given both behavioural and neuropsychological tests of emotion processing. The behavioural task examined expression regulation knowledge (ERK) for prosocial and self-presentational hypothetical interactions. The chimeric faces test was given as a measure of lateralisation for processing positive facial emotion. An interaction between age and lateralisation for emotion processing was predictive of children's ERK for only the self-presentational interactions. The relationships between children's ERK and lateralisation for emotion processing changes across the three age groups, emerging as a positive relationship in the 10-year-olds. The 10-years-olds who were more lateralised to the right hemisphere for emotion processing tended to show greater understanding of the need for regulating negative emotions during interactions that would have a self-presentational motivation. This finding suggests an association between the behavioural and neuropsychological development of emotion processing.     

The perception of positive and negative facial expressions in unilateral brain-damaged patients: A meta-analysis

How the brain is lateralised for emotion processing remains a key question in contemporary neuropsychological research. The right hemisphere hypothesis asserts that the right hemisphere dominates emotion processing, whereas the valence hypothesis holds that positive emotion is processed in the left hemisphere and negative emotion is controlled by the right hemisphere. A meta-analysis was conducted to assess unilateral brain-damaged individuals’ performance on tasks of facial emotion perception according to valence. A systematic search of the literature identified seven articles that met the conservative selection criteria and could be included in a meta-analysis. A total of 12 meta-analyses of facial expression perception were constructed assessing identification and labelling tasks according to valence and the side of brain damage. The results demonstrated that both left and right hemisphere damage leads to impairments in emotion perception (identification and labelling) irrespective of valence. Importantly, right hemisphere damage prompted more pronounced emotion perception impairment than left hemisphere damage, across valence, suggesting right hemisphere dominance for emotion perception. Furthermore, right hemisphere damage was associated with a larger tendency for impaired perception of negative than positive emotion across identification and labelling tasks. Overall the findings support Adolphs, Jansari, and Tranel (2001) model whereby the right hemisphere preferentially processes negative facial expressions and both hemispheres process positive facial expressions.     

Where were those rabbits? A new paradigm to determine cerebral lateralisation of visuospatial memory function in children

In the majority of people, functional differences are observed between the two cerebral hemispheres: language production is typically subserved by the left hemisphere and visuospatial skills by the right hemisphere. The development of this division of labour is not well understood and lateralisation of visuospatial function has received little attention in children. In this study we devised a child-friendly version of a paradigm to assess lateralisation of visuospatial memory using functional transcranial Doppler ultrasound (fTCD). In a group of 24 adults we found this child-friendly version gave similar results to the original version of the task. In addition, fourteen children aged 6-8 years successfully completed the child-friendly fTCD task, showing a negative lateralisation index, indicating right hemispheric specialisation at the group level. Additionally, we assessed effects of task accuracy and reaction time on the lateralisation index. No effects were found, at the group level or at the level of single trials, in either the adult or the child group. We conclude that this new task reliably assesses lateralisation of visuospatial memory function in children as young as 6 years of age, using fTCD. As such, it holds promise for investigating development of lateralisation of visuospatial function in typically and atypically developing children.     

Left-sided oral asymmetries in spontaneous but not posed smiles

To investigate possible facial asymmetries during the production of posed and spontaneous smiles, the displacement of various reference points on the mouth were measured as subjects produced both kinds of smiles. Strobe cameras were used in combination with a computer-based analysis to record the smiles of left- and right-handed males and females. The analysis revealed that the left side of the mouth moved more than the right side during spontaneous but not posed smiles, supporting the notion that the right hemisphere may play a special role in emotional expression. This asymmetry was most apparent in left-handed females and right-handed males. These sex and handedness differences are discussed with reference to apparent inconsistencies in previous research on asymmetries in emotional expression.     

Lateralization for the expression and perception of facial emotion as a function of age

In order to test the hypothesis of right hemisphere changes with age, this study examined lateralization for facial emotion in young, middle-aged, and older women (N = 90). For expression, subjects were photographed while posing positive and negative emotions. Composite photographs were created and rated for intensity. For perception, subjects were required to make intensity judgements about emotional chimeric faces. Overall, subjects demonstrated significant left-sided facial asymmetry for expression and significant left hemispace biases for perception. The findings for facial expression were not influenced by emotional valence or resting face asymmetries. There were no changes in lateralization as a function of age for either expression or perception. Taken together, these findings lend support to the notion that the right hemisphere mediates emotional processing across the adult life span.     

Lateralisation for processing facial emotion and anxiety: contrasting state, trait and social anxiety

Recent neuropsychological studies have attempted to distinguish between different types of anxiety by contrasting patterns of brain organisation or activation; however, lateralisation for processing emotional stimuli has received relatively little attention. This study examines the relationship between strength of lateralisation for the processing of facial expressions of emotion and three measures of anxiety: state anxiety, trait anxiety and social anxiety. Across all six of the basic emotions (anger, disgust, fear, happiness, sadness, surprise) the same patterns of association were found. Participants with high levels of trait anxiety were more strongly lateralised to the right hemisphere for processing facial emotion. In contrast, participants with high levels of self-reported physiological arousal in response to social anxiety were more weakly lateralised to the right hemisphere, or even lateralised to the left hemisphere, for the processing of facial emotion. There were also sex differences in these associations: the relationships were evident for males only. The finding of distinct patterns of lateralisation for trait anxiety and self-reported physiological arousal suggests different neural circuitry for trait and social anxiety.