Something to sink your teeth into: The presence of teeth augments ERPs to mouth expressions

Beyond facial expressions: A systematic review on effects of emotional relevance of faces on the N170

The N170 is the most prominent electrophysiological signature of face processing. While facial expressions reliably modulate the N170, there is considerable variance in N170 modulations by other sources of emotional relevance. Therefore, we systematically review and discuss this research area using different methods to manipulate the emotional relevance of inherently neutral faces. These methods were categorized into (1) existing pre-experimental affective person knowledge (e.g., negative attitudes towards outgroup faces), (2) experimentally instructed affective person knowledge (e.g., negative person information), (3) contingency-based affective learning (e.g., fear-conditioning), or (4) the immediate affective context (e.g., emotional information directly preceding the face presentation). For all categories except the immediate affective context category, the majority of studies reported significantly increased N170 amplitudes depending on the emotional relevance of faces. Furthermore, the potentiated N170 was observed across different attention conditions, supporting the role of the emotional relevance of faces on the early prioritized processing of configural facial information, regardless of low-level differences. However, we identified several open research questions and suggest venues for further research.

The influence of selective attention to specific emotions on the processing of faces as revealed by event-related brain potentials

Event-related potential studies using affective words have indicated that selective attention to valence can increase affective discrimination at early perceptual stages. This effect most likely relies on neural associations between perceptual features of a stimulus and its affective value. Similar to words, emotional expressions in human faces are linked to specific visual elements. Therefore, selectively attending to a given emotion should allow for the preactivation of neural networks coding for the emotion and associated first-order visual elements, leading to enhanced early processing of faces expressing the attended emotion. To investigate this, we employed an expression detection task (N = 65). Fearful, happy, and neutral faces were randomly presented in three blocks while participants were instructed to respond only to one predefined target level of expression in each block. Reaction times were the fastest for happy target faces, which was accompanied by an increased occipital P1 for happy compared with fearful faces. The N170 yielded an arousal effect (emotional > neutral) while both components were not modulated by target status. In contrast, the early posterior negativity (EPN) arousal effect tended to be larger for target compared with nontarget faces. The late positive potential (LPP) revealed large effects of status and expression as well as an interaction driven by an increased LPP specifically for nontarget fearful faces. These findings tentatively indicate that selective attention to facial affect may enhance early emotional processing (EPN) even though further research is needed. Moreover, late controlled processing of facial emotions appears to involve a negativity bias.

The impact of emotional facial expressions on reflexive attention depends on the aim of dynamic gaze changes: An ERP study

The emotional expression and gaze direction of a face are important cues for human social interactions. However, the interplay of these factors and their neural correlates are only partially understood. In the current study, we investigated ERP correlates of gaze and emotion processing following the initial presentation of faces with different emotional expressions (happy, neutral, angry) and an averted or direct gaze direction as well as following a subsequent change in gaze direction that occurred in half of the trials. We focused on the time course and scalp topography of the N170 and EPN components. The N170 amplitude was larger to averted than direct gaze for the initial face presentation and larger to gaze changes from direct to averted than from averted to direct in response to the gaze change. For the EPN component in response to the initial face presentation, we replicate classic effects of emotion, which did not interact with gaze direction. As a major new finding, changes from direct to averted gaze elicited an EPN-like effect when the face showed a happy expression. No such effect was seen for angry expressions. We conclude that happy faces reflexively attract attention when they look at the observer rather than away from the observer. These results for happy expressions are in line with the shared signal hypothesis that posits a better processing of expressions if their approach or avoidance tendency is consistent with gaze direction. However, the shared signal hypothesis is not supported by the present results for angry faces.

Potentiated early neural responses to fearful faces are not driven by specific face parts

Prioritized processing of fearful compared to neutral faces is reflected in increased amplitudes of components of the event-related potential (ERP). It is unknown whether specific face parts drive these modulations. Here, we investigated the contributions of face parts on ERPs to task-irrelevant fearful and neutral faces using an ERP-dependent facial decoding technique and a large sample of participants (N = 83). Classical ERP analyses showed typical and robust increases of N170 and EPN amplitudes by fearful relative to neutral faces. Facial decoding further showed that the absolute amplitude of these components, as well as the P1, was driven by the low-frequency contrast of specific face parts. However, the difference between fearful and neutral faces was not driven by any specific face part, as supported by Bayesian statistics. Furthermore, there were no correlations between trait anxiety and main effects or interactions. These results suggest that increased N170 and EPN amplitudes to task-irrelevant fearful compared to neutral faces are not driven by specific facial regions but represent a holistic face processing effect.

Emotion and attention in face processing: Complementary evidence from surface event-related potentials and intracranial amygdala recordings

Face processing is biased by emotional and voluntarily directed attention, both of which modulate processing in distributed cortical areas. The amygdala is assumed to contribute to an attentional bias for emotional faces, although its interaction with directed attention awaits further clarification. Here, we studied the interaction of emotion and attention during face processing via scalp EEG potentials of healthy participants and intracranial EEG (iEEG) recordings of the right amygdala in one patient. Three randomized blocks consisting of angry, neutral, and happy facial expressions were presented, and one expression was denoted as the target category in each block. Happy targets were detected fastest and most accurately both in the group study and by the iEEG patient. Occipital scalp potentials revealed emotion differentiation for happy faces in the early posterior negativity (EPN) around 300 ms after stimulus onset regardless of the target condition. A similar response to happy faces occurred in the amygdala only for happy targets. On the scalp, a late positive potential (LPP, around 600 ms) enhancement for targets occurred for all target conditions alike. A simultaneous late signal in the amygdala was largest for emotional targets. No late signal enhancements were found for neutral targets in the amygdala. Cortical modulations, by contrast, showed both attention-independent effects of emotion and emotion-independent effects of attention. These results demonstrate an attention-dependence of amygdala activity during the processing of facial expressions and partly independent cortical mechanisms.

Early Influence of Emotional Scenes on the Encoding of Fearful Expressions With Different Intensities: An Event-Related Potential Study

Contextual affective information influences the processing of facial expressions at the relatively early stages of face processing, but the effect of the context on the processing of facial expressions with varying intensities remains unclear. In this study, we investigated the influence of emotional scenes (fearful, happy, and neutral) on the processing of fear expressions at different levels of intensity (high, medium, and low) during the early stages of facial recognition using event-related potential (ERP) technology. EEG data were collected while participants performed a fearful facial expression recognition task. The results showed that (1) the recognition of high-intensity fear expression was higher than that of medium- and low-intensity fear expressions. Facial expression recognition was the highest when faces appeared in fearful scenes. (2) Emotional scenes modulated the amplitudes of N170 for fear expressions with different intensities. Specifically, the N170 amplitude, induced by high-intensity fear expressions, was significantly higher than that induced by low-intensity fear expressions when faces appeared in both neutral and fearful scenes. No significant differences were found between the N170 amplitudes induced by high-, medium-, and low-intensity fear expressions when faces appeared in happy scenes. These results suggest that individuals may tend to allocate their attention resources to the processing of face information when the valence between emotional context and expression conflicts i.e., when the conflict is absent (fear scene and fearful faces) or is low (neutral scene and fearful faces).

Monitoring the effect of oxytocin on the neural sensitivity to emotional faces via frequency-tagging EEG: A double-blind, cross-over study

The neuropeptide oxytocin (OXT) is suggested to exert an important role in human social behaviors by modulating the salience of social cues. To date, however, there is mixed evidence whether a single dose of OXT can improve the behavioral and neural sensitivity for emotional face processing. To overcome difficulties encountered with classic event-related potential studies assessing stimulus-saliency, we applied frequency-tagging EEG to implicitly assess the effect of a single dose of OXT (24 IU) on the neural sensitivity for positive and negative facial emotions. Neutral faces with different identities were presented at 6 Hz, periodically interleaved with an expressive face (angry, fearful, and happy, in separate sequences) every fifth image (i.e., 1.2 Hz oddball frequency). These distinctive frequency tags for neutral and expressive stimuli allowed direct and objective quantification of the neural expression-categorization responses. The study involved a double-blind, placebo-controlled, cross-over trial with 31 healthy adult men. Contrary to our expectations, we did not find an effect of OXT on facial emotion processing, neither at the neural, nor at the behavioral level. A single dose of OXT did not evoke social enhancement in general, nor did it affect social approach-avoidance tendencies. Possibly ceiling performances in facial emotion processing might have hampered further improvement.

The role of phase and orientation for ERP modulations of spectrum-manipulated fearful and neutral faces

Prioritized processing of fearful compared to neutral faces has been proposed to result from evolutionary adaptation of the contrast sensitivity function (CSF) to the features of emotionally relevant faces and/or vice versa. However, it is unknown whether a stimulus merely has to feature the amplitude spectrum of a fearful face to be prioritized or whether the relevant spatial frequencies have to occur with specific phases and orientations. Prioritized processing is indexed by specific increases of Event-Related Potentials (ERPs) of the EEG and occurs throughout different early processing stages, indexed by emotion-related modulations of the P1, N170, and EPN. In this pre-registered study, we manipulated phase and amplitude properties of the Fourier spectra of neutral and fearful faces to test the effect of phase coherence (PC, face vs. scramble) and orientation coherence (OC, original vs. rotational average) and their interactions with differential emotion processing. We found that differential emotion processing was not present at the level of P1 but strongly affected N170 and EPN. In both cases, intact phase coherence was required for enhanced processing of fearful faces. OC did not interact with emotion. While faces produced the typical N170 effect, we observed a reversed effect for scrambles. Additional exploratory independent component analysis (ICA) suggests that this reversal could signal a mismatch between an early "perceptual hypothesis" and feedback of configural information. In line with our expectations, fearful-neutral differences for the N170 and EPN depend on configural information, i.e., recognizable faces.

A Preliminary Investigation of ERP Components of Attentional Bias in Anxious Adults using Temporospatial Principal Component Analysis

Threat-related attention bias is thought to contribute to the development and maintenance of anxiety disorders. Dot-probe studies using event-related potentials (ERPs) have indicated that several early ERP components are modulated by threatening and emotional stimuli in anxious populations, suggesting enhanced allocation of attention to threat and emotion at earlier stages of processing. However, ERP components selected for examination and analysis in these studies vary widely and remain inconsistent. The present study used temporospatial principal component analysis (PCA) to systematically identify ERP components elicited to face pair cues and probes in a dot-probe task in anxious adults. Cue-locked components sensitive to emotion included an early occipital C1 component enhanced for happy versus angry face pair cues and an early parieto-occipital P1 component enhanced for happy versus angry face pair cues. Probe-locked components sensitive to congruency included a parieto-occipital P2 component enhanced for incongruent probes (probes replacing neutral faces) versus congruent probes (probes replacing emotional faces). Split-half correlations indicated that the mean value around the PCA-derived peaks were reliably measured in the ERP waveforms. These results highlight promising neurophysiological markers for attentional bias research that can be extended to designs comparing anxious and healthy comparison groups. Results from a secondary exploratory PCA analysis investigating the effects of emotional face position and analyses on behavioral reaction time data are also presented.

Emotion, Gender and Gaze Discrimination Tasks do not Differentially Impact the Neural Processing of Angry or Happy Facial Expressions-a Mass Univariate ERP Analysis

Facial expression processing is a critical component of social cognition yet, whether it is influenced by task demands at the neural level remains controversial. Past ERP studies have found mixed results with classic statistical analyses, known to increase both Type I and Type II errors, which Mass Univariate statistics (MUS) control better. However, MUS open-access toolboxes can use different fundamental statistics, which may lead to inconsistent results. Here, we compared the output of two MUS toolboxes, LIMO and FMUT, on the same data recorded during the processing of angry and happy facial expressions investigated under three tasks in a within-subjects design. Both toolboxes revealed main effects of emotion during the N170 timing and main effects of task during later time points typically associated with the LPP component. Neither toolbox yielded an interaction between the two factors at the group level, nor at the individual level in LIMO, confirming that the neural processing of these two face expressions is largely independent from task demands. Behavioural data revealed main effects of task on reaction time and accuracy, but no influence of expression or an interaction between the two. Expression processing and task demands are discussed in the context of the consistencies and discrepancies between the two toolboxes and existing literature.

From Gaze Perception to Social Cognition: The Shared-Attention System

When two people look at the same object in the environment and are aware of each other's attentional state, they find themselves in a shared-attention episode. This can occur through intentional or incidental signaling and, in either case, causes an exchange of information between the two parties about the environment and each other's mental states. In this article, we give an overview of what is known about the building blocks of shared attention (gaze perception and joint attention) and focus on bringing to bear new findings on the initiation of shared attention that complement knowledge about gaze following and incorporate new insights from research into the sense of agency. We also present a neurocognitive model, incorporating first-, second-, and third-order social cognitive processes (the shared-attention system, or SAS), building on previous models and approaches. The SAS model aims to encompass perceptual, cognitive, and affective processes that contribute to and follow on from the establishment of shared attention. These processes include fundamental components of social cognition such as reward, affective evaluation, agency, empathy, and theory of mind.

The early processing of fearful and happy facial expressions is independent of task demands - Support from mass univariate analyses

Most ERP studies on facial expressions of emotion have yielded inconsistent results regarding the time course of emotion effects and their possible modulation by task demands. Most studies have used classical statistical methods with a high likelihood of type I and type II errors, which can be limited with Mass Univariate statistics. FMUT and LIMO are currently the only two available toolboxes for Mass Univariate analysis of ERP data and use different fundamental statistics. Yet, no direct comparison of their output has been performed on the same dataset. Given the current push to transition to robust statistics to increase results replicability, here we compared the output of these toolboxes on data previously analyzed using classic approaches (Itier & Neath-Tavares, 2017). The early (0-352 ms) processing of fearful, happy, and neutral faces was investigated under three tasks in a within-subject design that also controlled gaze fixation location. Both toolboxes revealed main effects of emotion and task but neither yielded an interaction between the two, confirming the early processing of fear and happy expressions is largely independent of task demands. Both toolboxes found virtually no difference between neutral and happy expressions, while fearful (compared to neutral and happy) expressions modulated the N170 and EPN but elicited maximum effects after the N170 peak, around 190 ms. Similarities and differences in the spatial and temporal extent of these effects are discussed in comparison to the published classical analysis and the rest of the ERP literature.

The Effects of Dynamic and Static Emotional Facial Expressions of Humans and Their Avatars on the EEG: An ERP and ERD/ERS Study

This study aimed to examine whether the cortical processing of emotional faces is modulated by the computerization of face stimuli ("avatars") in a group of 25 healthy participants. Subjects were passively viewing 128 static and dynamic facial expressions of female and male actors and their respective avatars in neutral or fearful conditions. Event-related potentials (ERPs), as well as alpha and theta event-related synchronization and desynchronization (ERD/ERS), were derived from the EEG that was recorded during the task. All ERP features, except for the very early N100, differed in their response to avatar and actor faces. Whereas the N170 showed differences only for the neutral avatar condition, later potentials (N300 and LPP) differed in both emotional conditions (neutral and fear) and the presented agents (actor and avatar). In addition, we found that the avatar faces elicited significantly stronger reactions than the actor face for theta and alpha oscillations. Especially theta EEG frequencies responded specifically to visual emotional stimulation and were revealed to be sensitive to the emotional content of the face, whereas alpha frequency was modulated by all the stimulus types. We can conclude that the computerized avatar faces affect both, ERP components and ERD/ERS and evoke neural effects that are different from the ones elicited by real faces. This was true, although the avatars were replicas of the human faces and contained similar characteristics in their expression.

Reduced early fearful face processing during perceptual distraction in high trait anxious participants

Fearful facial expressions are prioritized across different stages of information processing as reflected by early, mid-latency, and late components of event-related brain potentials (ERP). Trait anxiety has been proposed to modulate these responses, but it is yet unclear how such modulations depend on feature-based attention. In this preregistered study (N = 80), we investigated the effects of trait anxiety on ERP differences between fearful and neutral faces across three different tasks. Participants had to discriminate either the orientation of lines overlaid onto the faces, the gender of the face, or the emotional expression, thus increasing attention to emotionally relevant facial features across the tasks. Fearful versus neutral faces elicited increased P1 and N170 amplitudes across tasks and potentiated amplitudes when attention was directed to faces (early posterior negativity [EPN]) or the expression (EPN and late positive potential). Higher trait anxiety was related to smaller EPN differences between fearful and neutral faces during the perceptual discrimination task. This early relationship suggests reduced instead of amplified processing of fearful faces for high trait anxious participants under perceptual distraction.

The influence of mouth opening and closing degrees on processing in NimStim facial expressions: An ERP study from Chinese college students

The degree of mouth opening and closing is one of the most important attributes of expression, reflecting the intensity of facial expression and can assist people to recognize the expression more accurately. The NimStim set of facial expressions contains the open and closed expression pictures of the same actor. Although this expression set has been widely used, there is little research on the intensity effect of this set. In this study, 32 Chinese college students were recruited in to view the pictures passively in an ERP experiment, aiming to investigate the intensity effect in the NimStim set (mouth open, mouth closed) of anger, disgust, sad, happy and neutral expression in electrical physiological aspects of the reaction. Our results reported that intensity of expression early affected in VPP and mainly affected in LPP with the open mouth having a larger activity. And there was no intensity effect found in P1, N170 and EPN. Notably, culture and social environment may influence the intensity effect of different emotions. In future, researchers should use methods that ensure subjects pay more attention to the intensity effect of the NimStim facial set.

Effects of low-level visual information and perceptual load on P1 and N170 responses to emotional expressions

Emotional facial expressions lead to modulations of early event-related potentials (ERPs). However, it has so far remained unclear how far these modulations represent face-specific effects rather than differences in low-level visual features, and to which extent they depend on available processing resources. To examine these questions, we conducted two preregistered independent experiments (N = 40 in each experiment) using different variants of a novel task that manipulates peripheral perceptual load across levels but keeps overall visual stimulation constant. At the display center, we presented task-irrelevant angry, neutral, and happy faces and their Fourier phase-scrambled versions, which preserved low-level visual features. The results of both studies showed load-independent P1 and N170 emotional expression effects. Importantly, by using Bayesian analyses we could confirm that these facial expression effects were face-independent for the P1 but not for the N170 component. We conclude that firstly, ERP modulations during the P1 interval strongly depend on low-level visual information, while the N170 modulation requires the processing of figural facial expression features. Secondly, both P1 and N170 modulations appear to be immune to a large range of variations in perceptual load.

Attentional conditions differentially affect early, intermediate and late neural responses to fearful and neutral faces

The processing of fearful facial expressions is prioritized by the human brain. This priority is maintained across various information processing stages as evident in early, intermediate and late components of event-related potentials (ERPs). However, emotional modulations are inconsistently reported for these different processing stages. In this pre-registered study, we investigated how feature-based attention differentially affects ERPs to fearful and neutral faces in 40 participants. The tasks required the participants to discriminate either the orientation of lines overlaid onto the face, the sex of the face or the face's emotional expression, increasing attention to emotion-related features. We found main effects of emotion for the N170, early posterior negativity (EPN) and late positive potential (LPP). While N170 emotional modulations were task-independent, interactions of emotion and task were observed for the EPN and LPP. While EPN emotion effects were found in the sex and emotion tasks, the LPP emotion effect was mainly driven by the emotion task. This study shows that early responses to fearful faces are task-independent (N170) and likely based on low-level and configural information while during later processing stages, attention to the face (EPN) or-more specifically-to the face's emotional expression (LPP) is crucial for reliable amplified processing of emotional faces.

Updating facial emotional expressions in working memory: Differentiating trait anxiety and depressiveness

Individual differences in updating emotional facial expressions in working memory are not fully understood. Here we focused on the effects of high trait anxiety and high depressiveness in men and women on updating schematic emotional facial expressions (sad, angry, scheming, happy, neutral). A population representative sample of young adults was divided into four emotional disposition groups based on STAI-T and MADRS cut-offs: high anxiety (HA, n = 41), high depressiveness (HD, n = 31), high depressiveness & high anxiety (HAHD, n = 65) and control (CT, n = 155). Participants completed a 2-back task with schematic emotional faces, and valence/arousal ratings and verbal recognition tasks. A novel approach was used to separate encoding from retrieval. We found an interaction of emotional dispositions and emotional faces in updating accuracy. HD group made more errors than HA when encoding happy schematic faces. Other differences between emotional dispositions on updating measures were found but they were not specific to any emotional facial expression. Our findings suggest that there is a minor happy disadvantage in HD in contrast to HA which can be seen in lower accuracy for visual encoding of happy faces, but not in retrieval accuracy, the speed of updating, nor perception of emotional content in happy faces. These findings help to explain differences and similarities between high trait anxiety and high depressiveness in working memory and processing of facial expressions. The results are discussed in relation to prevalent theories of information processing in anxiety and depression.

Transcranial magnetic stimulation demonstrates a role for the ventrolateral prefrontal cortex in emotion perception

The lateral prefrontal cortex, a region with both structural and functional connectivity to the amygdala, has been consistently implicated in the downregulation of subcortical-generated emotional responses. Although previous work has demonstrated that the ventral lateral prefrontal cortex (vlPFC) is important to emotion processing, no study has interrupted vlPFC function in order to test is role in emotion perception. In the current study, we acutely disrupted vlPFC function in twenty healthy adult participants by administering sham stimulation and transcranial magnetic stimulation (TMS), in randomized order, during performance of an emotional perception task. During sham stimulation, participants demonstrated increased perceptual sensitivity for happy faces compared to angry faces. Disruption of the vlPFC eliminated this difference: in this condition, perceptual sensitivity did not differ between happy and angry faces. Reaction times and response bias did not differ between emotions or TMS conditions. This pattern of perceptual bias is consistent with effects observed in a wide range of affective disorders, in which vlPFC dysfunction has also been reported. This study provides insight into a possible mechanism through which the vlPFC may contribute to emotion perception.

Fast Periodic Visual Stimulation EEG Reveals Reduced Neural Sensitivity to Fearful Faces in Children with Autism

We objectively quantified the neural sensitivity of school-aged boys with and without autism spectrum disorder (ASD) to detect briefly presented fearful expressions by combining fast periodic visual stimulation with frequency-tagging electroencephalography. Images of neutral faces were presented at 6 Hz, periodically interleaved with fearful expressions at 1.2 Hz oddball rate. While both groups equally display the face inversion effect and mainly rely on information from the mouth to detect fearful expressions, boys with ASD generally show reduced neural responses to rapid changes in expression. At an individual level, fear discrimination responses predict clinical status with an 83% accuracy. This implicit and straightforward approach identifies subtle deficits that remain concealed in behavioral tasks, thereby opening new perspectives for clinical diagnosis.

Task Demands Modulate Effects of Threatening Faces on Early Perceptual Encoding

The threat capture hypothesis states that threatening stimuli are automatically processed with higher priority than non-threatening stimuli, irrespective of observer intentions or focus of attention. We evaluated the threat capture hypothesis with respect to the early perceptual stages of face processing. We focused on an electrophysiological marker of face processing (the lateralized N170) in response to neutral, happy, and angry facial expressions displayed in competition with a non-face stimulus (a house). We evaluated how effects of facial expression on the lateralized N170 were modulated by task demands. In the pixel task, participants were required to identify the gender of the face, which made the face task-relevant and entailed structural encoding of the face stimulus. In the pixel task, participants identified the location of a missing pixel in the fixation cross, which made the face task-irrelevant and placed it outside the focus of attention. When faces were relevant, the lateralized N170 to angry faces was enhanced compared to happy and neutral faces. When faces were irrelevant, facial expression had no effect. These results reveal the critical role of task demands on the preference for threatening faces, indicating that top-down, voluntary processing modulates the prioritization of threat.

Length of Hair Affects P1 and N170 Latencies for Perception of Women's Faces

This study investigated the relationship between length of hair in facial stimuli and latency and amplitude of the P1 and N170 components of event-related potentials during facial perception. Electroencephalography was recorded from 21 Japanese participants (four men, 17 women) who were shown pictures of faces with one of three lengths of hair: long, medium length, or short. In addition, we used both fixed-size and variable-size blocks. In fixed-size blocks, the three types of stimuli were matched to have the same overall size; in variable-size blocks, long hair stimuli were the biggest, medium length hair stimuli were medium sized, and short hair stimuli were the smallest. We analyzed P1 latency and amplitude using two-way (6 × 2) repeated-measures analysis of variance over length of hair and electrode; N170 latency and amplitude were analyzed using three-way (6 × 2 × 2) repeated-measures analysis of variance over length of hair, hemisphere, and electrode. The latency of P1 to faces with short hair in variable-size blocks was significantly longer than that to the other five stimulus types ( p < .01 for four of the other types; p = .083 for medium length hair in variable-size blocks). The latency of N170 to faces with long hair in variable-size blocks was significantly shorter than that to faces with medium length hair and short hair in variable-size blocks ( p = .026 and p = .086, respectively). These results indicate that length of hair influenced P1 and N170 latency, supporting the notion that length of hair is a significant external facial feature. Because long hair attracted participants' attention, there was early perceptual processing of this feature. In contrast, because short hair did not attract attention, perceptual processing of this feature was late.

The effect of mouth opening in emotional faces on subjective experience and the early posterior negativity amplitude

Previous studies have examined the role of the eye region in emotional expressions, but the mouth region is understudied. The main goal of this study was to examine how mouth opening in emotional faces affects subjective experience and early automatic attentional capture, as measured by the early posterior negativity (EPN) amplitude. Participants in two studies viewed angry, happy, and neutral faces with mouths open and closed while their electroencephalogram was recorded. Afterwards, participants indicated how unpleasant-pleasant (i.e., valence) and calming-arousing (i.e., arousal) each face made them feel. Angry and happy faces (and neutral faces to a lesser extent) with an open vs. closed mouth made observers feel more extreme valence and arousal. In addition, there generally was an EPN for angry and happy faces (and neutral faces to a lesser extent) with open vs. closed mouths, which suggests that emotional expressions with an open mouth capture early automatic attention more than expressions with a closed mouth. Finally, the effects of mouth opening were somewhat modulated by face gender, but not by observer gender. The current findings contribute to our knowledge of facial expressions and social interaction, but also have relevance for the growing fields of social robotics and digital animation.

The effects of social anxiety on emotional face discrimination and its modulation by mouth salience

People high in social anxiety experience fear of social situations due to the likelihood of social evaluation. Whereas happy faces are generally processed very quickly, this effect is impaired by high social anxiety. Mouth regions are implicated during emotional face processing, therefore differences in mouth salience might affect how social anxiety relates to emotional face discrimination. We designed an emotional facial expression recognition task to reveal how varying levels of sub-clinical social anxiety (measured by questionnaire) related to the discrimination of happy and fearful faces, and of happy and angry faces. We also categorised the facial expressions by the salience of the mouth region (i.e. high [open mouth] vs. low [closed mouth]). In a sample of 90 participants higher social anxiety (relative to lower social anxiety) was associated with a reduced happy face reaction time advantage. However, this effect was mainly driven by the faces with less salient closed mouths. Our results are consistent with theories of anxiety that incorporate an oversensitive valence evaluation system.

Face-to-face: Perceived personal relevance amplifies face processing

The human face conveys emotional and social information, but it is not well understood how these two aspects influence face perception. In order to model a group situation, two faces displaying happy, neutral or angry expressions were presented. Importantly, faces were either facing the observer, or they were presented in profile view directed towards, or looking away from each other. In Experiment 1 (n = 64), face pairs were rated regarding perceived relevance, wish-to-interact, and displayed interactivity, as well as valence and arousal. All variables revealed main effects of facial expression (emotional > neutral), face orientation (facing observer > towards > away) and interactions showed that evaluation of emotional faces strongly varies with their orientation. Experiment 2 (n = 33) examined the temporal dynamics of perceptual-attentional processing of these face constellations with event-related potentials. Processing of emotional and neutral faces differed significantly in N170 amplitudes, early posterior negativity (EPN), and sustained positive potentials. Importantly, selective emotional face processing varied as a function of face orientation, indicating early emotion-specific (N170, EPN) and late threat-specific effects (LPP, sustained positivity). Taken together, perceived personal relevance to the observer-conveyed by facial expression and face direction-amplifies emotional face processing within triadic group situations.

Early visual processing of snakes and angry faces: An ERP study

Snakes and angry faces are common fear stimuli and both elicit an Early Posterior Negativity (EPN) in the event-related potential, which indicates that they capture early automatic visual attention. But because snakes have been a predatory threat for primates since long before communication through facial expressions evolved, we tested the hypothesis that the EPN for snakes would be more pronounced than the EPN for angry faces. We carefully controlled for differences between reptiles and faces by using lizards and neutral faces as control stimuli. Participants viewed a rapid serial visual presentation of snakes (i.e., threatening reptiles), lizards (i.e., non-threatening reptiles), angry faces (i.e., threatening humans), and neutral faces (i.e., non-threatening humans). EPNs for snakes (vs. lizards) and angry (vs. neutral) faces started to develop around 120 ms after stimulus onset. The EPN was of the same size for snakes and angry faces between 150-225 ms, but was larger for snakes than for angry faces between 225-300 ms, which suggests that snakes capture more extensive early automatic attention than angry faces. These findings correspond with the notion that the visual system is specifically tuned to detect snakes because of the prolonged pressure of snakes on primate evolution.

Effects of task demands on the early neural processing of fearful and happy facial expressions

Task demands shape how we process environmental stimuli but their impact on the early neural processing of facial expressions remains unclear. In a within-subject design, ERPs were recorded to the same fearful, happy and neutral facial expressions presented during a gender discrimination, an explicit emotion discrimination and an oddball detection tasks, the most studied tasks in the field. Using an eye tracker, fixation on the face nose was enforced using a gaze-contingent presentation. Task demands modulated amplitudes from 200 to 350ms at occipito-temporal sites spanning the EPN component. Amplitudes were more negative for fearful than neutral expressions starting on N170 from 150 to 350ms, with a temporo-occipital distribution, whereas no clear effect of happy expressions was seen. Task and emotion effects never interacted in any time window or for the ERP components analyzed (P1, N170, EPN). Thus, whether emotion is explicitly discriminated or irrelevant for the task at hand, neural correlates of fearful and happy facial expressions seem immune to these task demands during the first 350ms of visual processing.

The perceptual saliency of fearful eyes and smiles: A signal detection study

Facial features differ in the amount of expressive information they convey. Specifically, eyes are argued to be essential for fear recognition, while smiles are crucial for recognising happy expressions. In three experiments, we tested whether expression modulates the perceptual saliency of diagnostic facial features and whether the feature's saliency depends on the face configuration. Participants were presented with masked facial features or noise at perceptual conscious threshold. The task was to indicate whether eyes (experiments 1-3A) or a mouth (experiment 3B) was present. The expression of the face and its configuration (i.e. spatial arrangement of the features) were manipulated. Experiment 1 compared fearful with neutral expressions, experiments 2 and 3 compared fearful versus happy expressions. The detection accuracy data was analysed using Signal Detection Theory (SDT), to examine the effects of expression and configuration on perceptual precision (d') and response bias (c), separately. Across all three experiments, fearful eyes were detected better (higher d') than neutral and happy eyes. Eyes were more precisely detected than mouths, whereas smiles were detected better than fearful mouths. The configuration of the features had no consistent effects across the experiments on the ability to detect expressive features. But facial configuration affected consistently the response bias. Participants used a more liberal criterion for detecting the eyes in canonical configuration and fearful expression. Finally, the power in low spatial frequency of a feature predicted its discriminability index. The results suggest that expressive features are perceptually more salient with a higher d' due to changes at the low-level visual properties, with emotions and configuration affecting perception through top-down processes, as reflected by the response bias.

Facial Cosmetics Exert a Greater Influence on Processing of the Mouth Relative to the Eyes: Evidence from the N170 Event-Related Potential Component

Cosmetic makeup significantly influences facial perception. Because faces consist of similar physical structures, cosmetic makeup is typically used to highlight individual features, particularly those of the eyes (i.e., eye shadow) and mouth (i.e., lipstick). Though event-related potentials have been utilized to study various aspects of facial processing, the influence of cosmetics on specific ERP components remains unclear. The present study aimed to investigate the relationship between the application of cosmetic makeup and the amplitudes of the P1 and N170 event-related potential components during facial perception tasks. Moreover, the influence of visual perception on N170 amplitude, was evaluated under three makeup conditions: Eye Shadow, Lipstick, and No Makeup. Electroencephalography was used to monitor 17 participants who were exposed to visual stimuli under each these three makeup conditions. The results of the present study subsequently demonstrated that the Lipstick condition elicited a significantly greater N170 amplitude than the No Makeup condition, while P1 amplitude was unaffected by any of the conditions. Such findings indicate that the application of cosmetic makeup alters general facial perception but exerts no influence on the perception of low-level visual features. Collectively, these results support the notion that the application of makeup induces subtle alterations in the processing of facial stimuli, with a particular effect on the processing of specific facial components (i.e., the mouth), as reflected by changes in N170 amplitude.