Minimal group membership biases early neural processing of emotional expressions.

Mere affiliation with a social group alters people's perception of other individuals. One suggested mechanism behind such influence is that group membership triggers divergent visual facial representations for in-group and out-group members, which could constrain face processing. Here, using electroencephalography (EEG) under functional magnetic resonance imagery (fMRI) during a group categorization task, we investigated the impact of mere affiliation to an arbitrary group on the processing of emotional faces. The results indicate that in- and out-group members trigger differential event-related potential activity, appearing 150 ms after presentation of group membership information, which correlated with medial prefrontal fMRI activity. Additionally, EEG activity in the earliest stages of face processing (30-100 ms after expression onset) dissociated unexpected group-related emotions (in-group anger and out-group joy) from expected ones and correlated with temporo-parietal junction fMRI activity. We discuss the possibility that such dissociation may result from top-down influences from divergent representations for in-group and out-group members. Taken together, the present results suggest that mere membership in an arbitrary group polarized expectations which constrain the first steps of face processing.

An Exploratory TMS Study on Prefrontal Lateralization in Valence Categorization of Facial Expressions.

Converging neuroimaging and patient data suggest that the dorsolateral prefrontal cortex (DLPFC) is involved in emotional processing. However, it is still not clear whether the DLPFC in the left and right hemisphere is differentially involved in emotion recognition depending on the emotion considered. Here we used transcranial magnetic stimulation (TMS) to shed light on the possible causal role of the left and right DLPFC in encoding valence of positive and negative emotional facial expressions. Participants were required to indicate whether a series of faces displayed a positive or negative expression, while TMS was delivered over the right DLPFC, the left DLPFC, and a control site (vertex). Interfering with activity in both the left and right DLPFC delayed valence categorization (compared to control stimulation) to a similar extent irrespective of emotion type. Overall, we failed to demonstrate any valence-related lateralization in the DLPFC by using TMS. Possible methodological limitations are discussed.

Emotion processing in early blind and sighted individuals.

OBJECTIVE: Emotion processing is known to be mediated by a complex network of cortical and subcortical regions with evidence of specialized hemispheric lateralization within the brain. In light of prior evidence indicating that lateralization of cognitive functions (such as language) may depend on normal visual development, we investigated whether the lack of prior visual experience would have an impact on the development of specialized hemispheric lateralization in emotional processing. METHOD: We addressed this issue by comparing performance in early blind and sighted controls on a dichotic listening task requiring the detection of specific emotional vocalizations (i.e., suggestive of happiness or sadness) presented independently to either ear. RESULTS: Consistent with previous studies, we found that sighted individuals showed enhanced detection of positive vocalizations when presented in the right ear (i.e., processed within the left hemisphere) and negative vocalizations when presented in the left ear (i.e., right hemisphere). It is interesting to note that although blind individuals were as accurate as sighted controls in detecting the valance of the vocalization, performance was not consistent with any pattern of specialized hemispheric lateralization. CONCLUSIONS: Overall, these results suggest that although the lack of prior visual experience may not lead to impaired emotion processing performance, the underlying neurophysiological substrate (i.e., degree of special hemispheric lateralization) may depend on normal visual development. (PsycINFO Database Record

Dorsomedial prefrontal cortex and cerebellar contribution to in-group attitudes: a transcranial magnetic stimulation study.

We tend to express more positive judgments and behaviors toward individuals belonging to our own group compared to other (out-) groups. In this study, we assessed the role of the cerebellum and of the dorsomedial prefrontal cortex (dmPFC) - two regions critically implicated in social cognition processes - in mediating implicit valenced attitudes toward in-group and out-group individuals. To this aim, we used transcranial magnetic stimulation (TMS) in combination with a standard attitude priming task, in which Caucasian participants had to categorize the valence of a series of adjectives primed by either an in-group or an out-group face. In two behavioral experiments, we found an in-group bias (i.e. faster categorization of positive adjectives when preceded by in-group faces) but no evidence of an out-group bias. Interestingly, TMS over both the dmPFC and over the (right) cerebellum significantly interfered with the modulation exerted by group membership on adjective valence classification, abolishing the in-group bias observed at baseline. Overall, our data suggest that both the dmPFC and the cerebellum play a causal role in mediating implicit social attitudes.

Selective attention effects on early integration of social signals: same timing, modulated neural sources.

Humans combine co-emitted social signals to predict other's immediate intentions and prepare an adapted response. However, little is known about whether attending to only one of co-emitted social signals impacts on its combination with other signals. Here, using electroencephalography, we address selective attention effects on early combination of social signals. We manipulated three visual cues: gaze direction, emotional expression, and pointing gesture, while participants performed either emotion or gaze direction judgments. Results showed that a temporal marker of social cues integration emerges 170ms after the stimulus onset, even if the integration of the three visual cues was not required to perform the task, as only one feature at a time was task relevant. Yet in addition to common temporal regions, the relative contribution of specific neural sources of this integration changed as a function of the attended feature: integration during emotion judgments was mainly implemented in classic limbic areas but in the dorsal pathway during gaze direction judgments. Together, these findings demonstrate that co-emitted social cues are integrated as long as they are relevant to the observer, even when they are irrelevant to the ongoing task.

Behavioral evidence for differences in social and non-social category learning.

When meeting someone for the very first time one spontaneously categorizes the seen person on the basis of his/her appearance. Categorization is based on the association between some physical features and category labels that can be social (character trait…) or non-social (tall, thin). Surprisingly little is known about how such associations are formed, particularly in the social domain. Here, we aimed at testing whether social and non-social category learning may be dissociated. We presented subjects with a large number of faces that had to be rated according to social or non-social labels, and induced an association between a facial feature (inter-eye distance) and the category labels using two different procedures. In a first experiment, we used a feedback procedure to reinforce the association; behavioral measures revealed an association between the physical feature manipulated and abstract non-social categories, while no evidence for an association with social labels could be found. In a second experiment, we used passive exposure to the association between physical features and labels; we obtained behavioral evidence for learning of both social and non-social categories. These results support the view of the specificity of social category learning; they suggest that social categories are best acquired through unsupervised procedures that can be considered as a simplified proxy for group transmission.

Early influence of prior experience on face perception.

Inferring someone's personality from his or her photograph is a pervasive and automatic behavior that takes place even if no reliable information about one's character can be derived solely from facial features. This illustrates nicely the idea that perception is not a passive process, but rather an active combination of current sensory inputs with endogenous knowledge derived from prior experience. To understand how and when neural responses to faces can be modulated by prior experience, we recorded magneto-encephalographic (MEG) responses to new faces, before and after subjects were exposed for a short period of 15-20 min to an experimentally induced association between a facial feature (inter-eye distance) and a response (personality judgment). In spite of the absence of any observable response bias following such a short reinforcement phase, our experimental manipulation influenced neural responses to faces as early as 60-85 ms. Source localization of magneto-encephalographic signals, confirmed by intracranial recordings, suggests that prior experience modulates early neural processing along two initially independent neural routes, one initiated in an anterior system that includes the orbitofrontal cortex and the temporal poles, and the second one involving face-sensitive regions in the ventral visual pathway. The two routes are both active as early as 60 ms but engage in reciprocal interactions only later, between 135 and 160 ms. These experimental findings support recent models assuming the existence of a fast anterior pathway activated in parallel with the ventral visual system which would link prior experience with current sensory inputs.