The valence-specific laterality effect in free viewing conditions: The influence of sex, handedness, and response bias

The right hemisphere has often been viewed as having a dominant role in the processing of emotional information. Other evidence indicates that both hemispheres process emotional information but their involvement is valence specific, with the right hemisphere dealing with negative emotions and the left hemisphere preferentially processing positive emotions. This has been found under both restricted (Reuter-Lorenz & Davidson, 1981) and free viewing conditions (Jansari, Tranel, & Adophs, 2000). It remains unclear whether the valence-specific laterality effect is also sex specific or is influenced by the handedness of participants. To explore this issue we repeated Jansari et al.'s free-viewing laterality task with 78 participants. We found a valence-specific laterality effect in women but not men, with women discriminating negative emotional expressions more accurately when the face was presented on the left-hand side and discriminating positive emotions more accurately when those faces were presented on the right-hand side. These results indicate that under free viewing conditions women are more lateralised for the processing of facial emotion than are men. Handedness did not affect the lateralised processing of facial emotion. Finally, participants demonstrated a response bias on control trials, where facial emotion did not differ between the faces. Participants selected the left-hand side more frequently when they believed the expression was negative and the right-hand side more frequently when they believed the expression was positive. This response bias can cause a spurious valence-specific laterality effect which might have contributed to the conflicting findings within the literature.     

A valence-specific lateral bias for discriminating emotional facial expressions in free field

Findings from subjects with unilateral brain damage, as well as from normal subjects studied with tachistoscopic paradigms, argue that emotion is processed differently by each brain hemisphere. An open question concerns the extent to which such lateralised processing might occur under natural, freeviewing conditions. To explore this issue, we asked 28 normal subjects to discriminate emotions expressed by pairs of faces shown side-by-side, with no time or viewing constraints. Images of neutral expressions were shown paired with morphed images of very faint emotional expressions (happiness, surprise, disgust, fear, anger, or sadness). We found a surprising and robust laterality effect: When discriminating negative emotional expressions, subjects performed significantly better when the emotional face was to the left of the neutral face; conversely, when discriminating positive expressions, subjects performed better when the emotional face was to the right. We interpret this valence-specific laterality effect as consistent with the idea that the right hemisphere is specialised to process negative emotions, whereas the left is specialised to process positive emotions. The findings have important implications for how humans perceive facial emotion under natural conditions.     

Valence specific laterality effects in free viewing conditions: the role of expectancy and gender of image

Recent research has looked at whether the expectancy of an emotion can account for subsequent valence specific laterality effects of prosodic emotion, though no research has examined this effect for facial emotion. In the study here (n=58), we investigated this issue using two tasks; an emotional face perception task and a novel word task that involved categorising positive and negative words. In the face perception task a valence specific laterality effect was found for surprise (positive) and anger (negative) faces in the control but not expectancy condition. Interestingly, lateralisation differed for face gender, revealing a left hemisphere advantage for male faces and a right hemisphere advantage for female faces. In the word task, an affective priming effect was found, with higher accuracy when valence of picture prime and word target were congruent. Target words were also responded to faster when presented to the LVF versus RVF in the expectancy but not control condition. These findings suggest that expecting an emotion influences laterality processing but that this differs in terms of the perceptual/experience dimension of the task. Further, that hemispheric processing of emotional expressions appear to differ in the gender of the image.     

Valence specific laterality effects in free viewing conditions: The role of expectancy and gender of image

Recent research has looked at whether the expectancy of an emotion can account for subsequent valence specific laterality effects of prosodic emotion, though no research has examined this effect for facial emotion. In the study here (n = 58), we investigated this issue using two tasks; an emotional face perception task and a novel word task that involved categorising positive and negative words. In the face perception task a valence specific laterality effect was found for surprise (positive) and anger (negative) faces in the control but not expectancy condition. Interestingly, lateralisation differed for face gender, revealing a left hemisphere advantage for male faces and a right hemisphere advantage for female faces. In the word task, an affective priming effect was found, with higher accuracy when valence of picture prime and word target were congruent. Target words were also responded to faster when presented to the LVF versus RVF in the expectancy but not control condition.These findings suggest that expecting an emotion influences laterality processing but that this differs in terms of the perceptual/experience dimension of the task. Further, that hemispheric processing of emotional expressions appear to differ in the gender of the image.     

Valence specific laterality effects in prosody: expectancy account and the effects of morphed prosody and stimulus lead

The majority of studies have demonstrated a right hemisphere (RH) advantage for the perception of emotions. Other studies have found that the involvement of each hemisphere is valence specific, with the RH better at perceiving negative emotions and the LH better at perceiving positive emotions [Reuter-Lorenz, P., & Davidson, R.J. (1981) Differential contributions of the 2 cerebral hemispheres to the perception of happy and sad faces. Neuropsychologia, 19, 609-613]. To account for valence laterality effects in emotion perception we propose an 'expectancy' hypothesis which suggests that valence effects are obtained when the top-down expectancy to perceive an emotion outweighs the strength of bottom-up perceptual information enabling the discrimination of an emotion. A dichotic listening task was used to examine alternative explanations of valence effects in emotion perception. Emotional sentences (spoken in a happy or sad tone of voice), and morphed-happy and morphed-sad sentences (which blended a neutral version of the sentence with the pitch of the emotion sentence) were paired with neutral versions of each sentence and presented dichotically. A control condition was also used, consisting of two identical neutral sentences presented dichotically, with one channel arriving before the other by 7 ms. In support of the RH hypothesis there was a left ear advantage for the perception of sad and happy emotional sentences. However, morphed sentences showed no ear advantage, suggesting that the RH is specialised for the perception of genuine emotions and that a laterality effect may be a useful tool for the detection of fake emotion. Finally, for the control condition we obtained an interaction between the expected emotion and the effect of ear lead. Participants tended to select the ear that received the sentence first, when they expected a 'sad' sentence, but not when they expected a 'happy' sentence. The results are discussed in relation to the different theoretical explanations of valence laterality effects in emotion perception.     

Valence-specific laterality effects in vocal emotion: interactions with stimulus type, blocking and sex

Valence-specific laterality effects have been frequently obtained in facial emotion perception but not in vocal emotion perception. We report a dichotic listening study further examining whether valence-specific laterality effects generalise to vocal emotions. Based on previous literature, we tested whether valence-specific laterality effects were dependent on blocked presentation of the emotion conditions, on the naturalness of the emotional stimuli, or on listener sex. We presented happy and sad sentences, paired with neutral counterparts, dichotically in an emotion localisation task, with vocal stimuli being preceded by verbal labels indicating target emotions. The measure was accuracy. When stimuli of the same emotion were presented as a block, a valence-specific laterality effect was demonstrated, but only in original stimuli and not morphed stimuli. There was a separate interaction with listener sex. We interpret our findings as suggesting that the valence-specific laterality hypothesis is supported only in certain circumstances. We discuss modulating factors, and we consider whether the mechanisms underlying those factors may be attentional or experiential in nature.     

The perception of positive and negative facial expressions by unilateral stroke patients

There remains conflict in the literature about the lateralisation of affective face perception. Some studies have reported a right hemisphere advantage irrespective of valence, whereas others have found a left hemisphere advantage for positive, and a right hemisphere advantage for negative, emotion. Differences in injury aetiology and chronicity, proportion of male participants, participant age, and the number of emotions used within a perception task may contribute to these contradictory findings. The present study therefore controlled and/or directly examined the influence of these possible moderators. Right brain-damaged (RBD; n = 17), left brain-damaged (LBD; n = 17), and healthy control (HC; n = 34) participants completed two face perception tasks (identification and discrimination). No group differences in facial expression perception according to valence were found. Across emotions, the RBD group was less accurate than the HC group, however RBD and LBD group performance did not differ. The lack of difference between RBD and LBD groups indicates that both hemispheres are involved in positive and negative expression perception. The inclusion of older adults and the well-defined chronicity range of the brain-damaged participants may have moderated these findings. Participant sex and general face perception ability did not influence performance. Furthermore, while the RBD group was less accurate than the LBD group when the identification task tested two emotions, performance of the two groups was indistinguishable when the number of emotions increased (four or six). This suggests that task demand moderates a study’s ability to find hemispheric differences in the perception of facial emotion.     

Visual-Field Bias in the Judgment of Facial Expression of Emotion

The left and right hemispheres of the brain are differentially related to the processing of emotions. Although there is little doubt that the right hemisphere is relatively superior for processing negative emotions, controversy exists over the hemispheric role in the processing of positive emotions. Eighty right-handed normal male participants were examined for visual-field (left-right) differences in the perception of facial expressions of emotion. Facial composite (RR, LL) and hemifacial (R, L) sets depicting emotion expressions of happiness and sadness were prepared. Pairs of such photographs were presented bilaterally for 150 ms, and participants were asked to select the photographs that looked more expressive. A left visual-field superiority (a right-hemisphere function) was found for sad facial emotion. A hemispheric advantage in the perception of happy expression was not found.     

Visual-field bias in the judgment of facial expression of emotion

The left and right hemispheres of the brain are differentially related to the processing of emotions. Although there is little doubt that the right hemisphere is relatively superior for processing negative emotions, controversy exists over the hemispheric role in the processing of positive emotions. Eighty right-handed normal male participants were examined for visual-field (left-right) differences in the perception of facial expressions of emotion. Facial composite (RR, LL) and hemifacial (R, L) sets depicting emotion expressions of happiness and sadness were prepared. Pairs of such photographs were presented bilaterally for 150 ms, and participants were asked to select the photographs that looked more expressive. A left visual-field superiority (a right-hemisphere function) was found for sad facial emotion. A hemispheric advantage in the perception of happy expression was not found.     

Laterality of facial expressions of emotion: Universal and culture-specific influences

Recent research indicates that (a) the perception and expression of facial emotion are lateralized to a great extent in the right hemisphere, and, (b) whereas facial expressions of emotion embody universal signals, culture-specific learning moderates the expression and interpretation of these emotions. In the present article, we review the literature on laterality and universality, and propose that, although some components of facial expressions of emotion are governed biologically, others are culturally influenced. We suggest that the left side of the face is more expressive of emotions, is more uninhibited, and displays culture-specific emotional norms. The right side of face, on the other hand, is less susceptible to cultural display norms and exhibits more universal emotional signals.     

The influence of emotional faces on the spatial allocation of attention

Background objectives: Studies suggest that the right hemisphere is dominant for emotional facial recognition. In addition, whereas some studies suggest the right hemisphere mediates the processing of all emotions (dominance hypothesis), other studies suggest that the left hemisphere mediates positive emotions the right mediates negative emotions (valence hypothesis). Since each hemisphere primarily attends to contralateral space, the goals of this study was to learn if emotional faces would induce a leftward deviation of attention and if the valence of facial emotional stimuli can influence the normal viewer’s spatial direction of attention. Methods: Seventeen normal right handed participants were asked to bisect horizontal lines that had all combinations of sad, happy or neutral faces at ends of these lines. During this task the subjects were never requested to look at these faces and there were no task demands that depended on viewing these faces. Results: Presentation of emotional faces induced a greater leftward deviation compared to neutral faces, independent of where (spatial position) these faces were presented. However, faces portraying negative emotions tended to induce a greater leftward bias than positive emotions. Conclusions: Independent of location, the presence of emotional faces influenced the spatial allocation of attention, such that normal subjects shift the direction of their attention toward left hemispace and this attentional shift appears to be greater for negative (sad) than positive faces (happy).     

Men appear more lateralized when noticing emotion in male faces

Empirical tests of the "right hemisphere dominance" versus "valence" theories of emotion processing are confounded by known sex differences in lateralization. Moreover, information about the sex of the person posing an emotion might be processed differently by men and women because of an adaptive male bias to notice expressions of threat and vigilance in other male faces. The purpose of this study was to investigate whether sex of poser and emotion displayed influenced lateralization in men and women by analyzing "laterality quotient" scores on a test which depicts vertically split chimeric faces, formed with one half showing a neutral expression and the other half showing an emotional expression. We found that men (N = 50) were significantly more lateralized for emotions indicative of vigilance and threat (happy, sad, angry, and surprised) in male faces relative to female faces and compared to women (N = 44). These data indicate that sex differences in functional cerebral lateralization for facial emotion may be specific to the emotion presented and the sex of face presenting it.     

情境对面孔表情识别的影响

长期以来,关于面孔表情识别的研究主要是围绕着面孔本身的结构特征来进行的,但是近年来的研究发现,面孔表情的识别也会受到其所在的情境背景（如语言文字、身体背景、自然与社会场景等）的影响,特别是在识别表情相似的面孔时,情境对面孔表情识别的影响更大。本文首先介绍和分析了近几年关于语言文字、身体动作、自然场景和社会场景等情境影响个体对面孔表情的识别的有关研究;其次,又分析了文化背景、年龄以及焦虑程度等因素对面孔表情识别情境效应的影响;最后,强调了未来的研究应重视研究儿童被试群体、拓展情绪的类别、关注真实生活中的面孔情绪感知等。     

A Voxel-based lesion study on facial emotion recognition after circumscribed prefrontal cortex damage

Previous studies have shown inconsistent findings regarding the contribution of the different prefrontal regions in emotion recognition. Moreover, the hemispheric lateralization hypothesis posits that the right hemisphere is dominant for processing all emotions regardless of affective valence, whereas the valence specificity hypothesis posits that the left hemisphere is specialized for processing positive emotions while the right hemisphere is specialized for negative emotions. However, recent findings suggest that the evidence for such lateralization has been less consistent. In this study, we investigated emotion recognition of fear, surprise, happiness, sadness, disgust, and anger in 30 patients with focal prefrontal cortex lesions and 30 control subjects. We also examined the impact of lesion laterality on recognition of the six basic emotions. The results showed that compared to control subjects, the frontal subgroups were impaired in recognition of three negative basic emotions of fear, sadness, and anger – regardless of the lesion laterality. Therefore, our findings did not establish that each hemisphere is specialized for processing specific emotions. Moreover, the voxel-based lesion symptom mapping analysis showed that recognition of fear, sadness, and anger draws on a partially common bilaterally distributed prefrontal network.     

Ratings of emotion in laterally presented faces: sex and handedness effects

Sixteen right-handed participants (8 male and 8 female students) and 16 left-handed participants (8 male and 8 female students) were presented with cartoon faces expressing emotions ranging from extremely positive to extremely negative. A forced-choice paradigm was used in which the participants were asked to rate the faces as either positive or negative. Compared to men, women rated faces more positively, especially in response to right visual field presentations. Women rated neutral and mildly positive faces more positively in the right than in the left visual field, whereas men rated these faces consistently across visual fields. Handedness did not affect the ratings of emotion. The data suggest a positive emotional bias of the left hemisphere in women.     

Perceptual and conceptual organization of facial emotions: Hemispheric differences

Patients with lesions to either the right or left hemisphere and control subjects were asked to judge the similarity of pairs of photographs of a person displaying different emotions, and of pairs of emotion words. The results were submitted to a multidimensional scaling analysis. Right-hemisphere-damaged subjects were found to be more impaired at perceiving facial emotions than were left-hemisphere-damaged subjects or controls, and this impairment was not confined to the perception of a subset of facial emotions nor to judging emotional valence (Pleasantness versus Unpleasantness). Rather, subtle impairments in perceiving a wide range of facial emotions were found, mostly concerning differentiation of the Positive-Negative and Attention-Rejection dimensions, and concerning the strategies the subjects used to make their judgments. The right-hemisphere-damaged subjects performed comparably to controls in their ratings of emotion words, suggesting that their ability to conceptualize emotional states was intact and that their impairment was strictly in the perception of emotion.     

How does context affect assessments of facial emotion? The role of culture and age

People from Asian cultures are more influenced by context in their visual processing than people from Western cultures. In this study, we examined how these cultural differences in context processing affect how people interpret facial emotions. We found that younger Koreans were more influenced than younger Americans by emotional background pictures when rating the emotion of a central face, especially those younger Koreans with low self-rated stress. In contrast, among older adults, neither Koreans nor Americans showed significant influences of context in their face emotion ratings. These findings suggest that cultural differences in reliance on context to interpret others' emotions depend on perceptual integration processes that decline with age, leading to fewer cultural differences in perception among older adults than among younger adults. Furthermore, when asked to recall the background pictures, younger participants recalled more negative pictures than positive pictures, whereas older participants recalled similar numbers of positive and negative pictures. These age differences in the valence of memory were consistent across culture.     

Mood-congruent false memories persist over time

There are two contrasting hypotheses that attempt to explain how emotion perception might be organised in the brain. One suggests that all emotions are lateralised to the right hemisphere whereas the other suggests that emotions may be differently lateralised according to valence. Here these two theories are contrasted, in addition to considering the role of emotional intensity in explaining possible differences in strength of lateralisation across emotions. Participants completed a Chimeric Faces Test for each of the six basic emotions: anger, disgust, fear, happiness, sadness and surprise. All emotions showed significant lateralisation to the right hemisphere, however, differences in strength of lateralisation within the right hemisphere were found. Stronger patterns of right hemisphere lateralisation were found for positive emotions and for emotions of higher intensity. The results support the right-hemisphere hypothesis, but suggest that there may be variability in organisation within the right hemisphere across different types of emotion.     

Mere social categorization modulates identification of facial expressions of emotion

The ability of the human face to communicate emotional states via facial expressions is well known, and past research has established the importance and universality of emotional facial expressions. However, recent evidence has revealed that facial expressions of emotion are most accurately recognized when the perceiver and expresser are from the same cultural ingroup. The current research builds on this literature and extends this work. Specifically, we find that mere social categorization, using a minimal-group paradigm, can create an ingroup emotion-identification advantage even when the culture of the target and perceiver is held constant. Follow-up experiments show that this effect is supported by differential motivation to process ingroup versus outgroup faces and that this motivational disparity leads to more configural processing of ingroup faces than of outgroup faces. Overall, the results point to distinct processing modes for ingroup and outgroup faces, resulting in differential identification accuracy for facial expressions of emotion.     

Perceiving arousal and valence in facial expressions: Differences between children and adults

Arousal and valence have long been studied as the two primary dimensions for the perception of emotional stimuli such as facial expressions. Prior correlational studies that tested emotion perception along these dimensions found broad similarities between adults and children. However, few studies looked for direct differences between children and adults in these dimensions beyond correlation. We tested 9-year-old children and adults on rating positive and negative facial stimuli based on emotional arousal and valence. Despite high significant correlations between children’s and adults’ ratings, our findings also showed significant differences between children and adults in terms of rating values: Children rated all expressions as significantly more positive than adults in valence. Children also rated positive emotions as more arousing than adults. Our results show that although perception of facial emotions along arousal and valence follows similar patterns in children and adults, some differences in ratings persist, and vary by emotion type.