Conflicts between priming and episodic retrieval: a question of fluency?

Human memory consists of different underlying processes whose interaction can result in counterintuitive findings. One phenomenon that relies on various types of mnemonic processes is the repetition priming effect for unfamiliar target faces in familiarity decisions, which is highly variable and may even reverse. Here, we tested the hypothesis that this reversed priming effect may be due to a conflict between target fluency signals and episodic retrieval processes. After replicating the reverse priming effect, three different manipulations were effective in diminishing it. We suggest that each of these manipulations diminished the ambiguity regarding the source of priming-induced fluency of target processing. Our findings argue against a strictly independent view of different types of memory.

Control over emotional facial expressions: Evidence from facial EMG and ERPs in a Stroop-like task

Facial expressions carry important social signals that must be precisely regulated despite potentially conflicting demands on veridicality, communicative intent, and the social situation. In a sample of 19 participants we investigated the challenges of deliberately controlling two facial expressions (smiles and frowns) by the emotional congruency with the expressions of adult and infant counterparts. In a Stroop-like task requiring participants' deliberate expressions of anger or happiness, we investigated the impact of task-irrelevant background pictures of adults and infants showing negative, neutral, or positive facial expressions. Participants' deliberate expressions were measured with electromyogram (EMG) of the M. zygomaticus major and M. corrugator supercilii. The latencies of EMG onsets revealed similar congruency effects for smiles and frowns with significant facilitation and inhibition components relative to the neutral condition. Interestingly, the facilitation effect for frown responses by negative facial expressions was significantly smaller vis a vis infant as compared to adult background faces. This diminished facilitation of frowns by infant's expressions of distress may relate to the activation of caregiver behavior or empathy. We investigated the neural correlates of the observed performance effects by recording event-related-potentials (ERPs). Increased amplitudes in ERP components were observed in incongruent relative to neutral conditions, revealing interference effects on both types of deliberate facial expressions, at different processing stages, namely, structural facial encoding (N170), conflict monitoring (N2), to semantic analysis (N400).

The other-race effect in facial expression processing: Behavioral and ERP evidence from a balanced cross-cultural study in women

Although evidence for cultural variants in facial expression decoding is accumulating, the other-race effect in facial expression processing and its neural correlates are still unclear. We investigated this question with a fully balanced design, in which a group of East Asian and a group of European Caucasian women categorized pictures of sad, happy, angry, and neutral facial expressions posed by individuals of their own-race and the other-race. Results revealed a disadvantage in categorizing expressions of anger in other-race faces in both samples, and for sad expressions in the European sample only. Partially consistent, East Asian participants showed longer latency of the N170 component in the event-related potential (ERP) and European Caucasian participants showed larger N170 amplitudes to other-race faces. The late positive complex in the ERP was less distinguishable among other-race facial expressions. Therefore, the present study observed an other-race effect in early and late stages of face processing, reflecting less efficient structural encoding and less elaborate processing for other-race than own-race faces.

Deliberate control over facial expressions in motherhood. Evidence from a Stroop-like task

The deliberate control of facial expressions is an important ability in human interactions, in particular for mothers with prelinguistic infants. Because research on this topic is still scarce, we investigated the control over facial expressions in a Stroop-like paradigm. Mothers of 2-6 months old infants and nullipara women produced smiles and frowns in response to verbal commands written on distractor faces of adults or infants showing expressions of happiness or anger/distress. Analyses of video recordings with a machine classifier for facial expression revealed pronounced effects of congruency between the expressions required by the participants and those displayed by the face stimuli on the onset latencies of the deliberate facial expressions. With adult distractor faces this Stroop effect was similar whether participants smiled or frowned. With infant distractor faces mothers and non-mothers showed indistinguishable Stroop effects on smile responses; however, for frown responses, the Stroop effect in mothers was smaller than in non-mothers. We suggest that for frown responses in mothers when facing infants, the effect of mimicry or stimulus response compatibility, leading to the Stroop effect, is offset by a caregiving response or empathy.

Effects of Social Context on Deliberate Facial Expressions: Evidence from a Stroop-like Task

Facial expressions contribute to nonverbal communication, social coordination, and interaction. Facial expressions may reflect the emotional state of the expressor, but they may be modulated by the presence of others, for example, by facial mimicry or through social display rules. We examined how deliberate facial expressions of happiness and anger (smiles and frowns), prompted by written commands, are modulated by the congruency with the facial expression of background faces and how this effect depends on the age of the background face (infants vs. adults). Our main interest was whether the quality of the required expression could be influenced by a task-irrelevant background face and its emotional display. Background faces from adults and infants displayed happy, angry, or neutral expressions. To assess the activation pattern of different action units, we used a machine classifier software; the same classifier was used to assess the chronometry of the expression responses. Results indicated slower and less correct performance when an incongruent facial expression was in the background, especially when distractor stimuli showed adult faces. Interestingly, smile responses were more intense in congruent than incongruent conditions. Depending on stimulus age, frown responses were affected in their quality by incongruent (smile) expressions in terms of the additional activation or deactivation of the outer brow raiser (AU2), resulting in a blended expression, somewhat different from the prototypical expression for anger. Together, the present results show qualitative effects on deliberate facial expressions, beyond typical chronometric effects, confirming machine classification of facial expressions as a promising tool for emotion research.

Human Observers and Automated Assessment of Dynamic Emotional Facial Expressions: KDEF-dyn Database Validation

Most experimental studies of facial expression processing have used static stimuli (photographs), yet facial expressions in daily life are generally dynamic. In its original photographic format, the Karolinska Directed Emotional Faces (KDEF) has been frequently utilized. In the current study, we validate a dynamic version of this database, the KDEF-dyn. To this end, we applied animation between neutral and emotional expressions (happy, sad, angry, fearful, disgusted, and surprised; 1,033-ms unfolding) to 40 KDEF models, with morphing software. Ninety-six human observers categorized the expressions of the resulting 240 video-clip stimuli, and automated face analysis assessed the evidence for 6 expressions and 20 facial action units (AUs) at 31 intensities. Low-level image properties (luminance, signal-to-noise ratio, etc.) and other purely perceptual factors (e.g., size, unfolding speed) were controlled. Human recognition performance (accuracy, efficiency, and confusions) patterns were consistent with prior research using static and other dynamic expressions. Automated assessment of expressions and AUs was sensitive to intensity manipulations. Significant correlations emerged between human observers' categorization and automated classification. The KDEF-dyn database aims to provide a balance between experimental control and ecological validity for research on emotional facial expression processing. The stimuli and the validation data are available to the scientific community.

Copycat of dynamic facial expressions: Superior volitional motor control for expressions of disgust

In social situations facial expressions are often strategically employed. Despite the many research on motor control of limb movements, little is known about the control over facial expressions. Using a response-priming task, we investigated motor control over three facial expressions, smiles, disgust and emotionally neutral jaw drops. Prime stimuli consisted of videos of a facial expression to be prepared or - as a neutral prime - an abstract symbol superimposed to a scrambled face. In valid trials an equal symbol (=) indicated to produce the primed expression. In invalid trials, an unequal symbol (‡) prompted participants to produce an alternative, unprimed expression. We examined the impact of emotion in preparing and revoking a prepared expression, and possible facilitation for dynamic facial expressions relative to symbolic primes. Participants' facial responses were scored using automated analyses of facial expressions with computer software. The underlying neurocognitive processes were tracked with event-related-potentials. Reprogramming costs, in the form of longer reaction times (RTs) in trials where participants had prepared an invalidly primed expression and had to quickly switch to the correct one, were more pronounced for smiles and jaw drops than for disgust, possibly indicating the need for being fast when showing disgust. Data from the P3 component related the behavioral effect to a more efficient updating of the correct response in brain systems responsible for motor control. Priming participants with dynamic facial expressions as examples for imitation, improved performance accuracy as compared to the symbolic abstract stimuli, but it not did affect RTs. Priming with dynamic videos also resulted in larger validity effects of the P3 component when disgust was the target response, indicating that the perceptual system might trigger automatic emotional responses, at least for negative affect.

Individual Differences in the Speed of Facial Emotion Recognition Show Little Specificity but Are Strongly Related with General Mental Speed: Psychometric, Neural and Genetic Evidence

Facial identity and facial expression processing are crucial socio-emotional abilities but seem to show only limited psychometric uniqueness when the processing speed is considered in easy tasks. We applied a comprehensive measurement of processing speed and contrasted performance specificity in socio-emotional, social and non-social stimuli from an individual differences perspective. Performance in a multivariate task battery could be best modeled by a general speed factor and a first-order factor capturing some specific variance due to processing emotional facial expressions. We further tested equivalence of the relationships between speed factors and polymorphisms of dopamine and serotonin transporter genes. Results show that the speed factors are not only psychometrically equivalent but invariant in their relation with the Catechol-O-Methyl-Transferase (COMT) Val158Met polymorphism. However, the 5-HTTLPR/rs25531 serotonin polymorphism was related with the first-order factor of emotion perception speed, suggesting a specific genetic correlate of processing emotions. We further investigated the relationship between several components of event-related brain potentials with psychometric abilities, and tested emotion specific individual differences at the neurophysiological level. Results revealed swifter emotion perception abilities to go along with larger amplitudes of the P100 and the Early Posterior Negativity (EPN), when emotion processing was modeled on its own. However, after partialling out the shared variance of emotion perception speed with general processing speed-related abilities, brain-behavior relationships did not remain specific for emotion. Together, the present results suggest that speed abilities are strongly interrelated but show some specificity for emotion processing speed at the psychometric level. At both genetic and neurophysiological levels, emotion specificity depended on whether general cognition is taken into account or not. These findings keenly suggest that general speed abilities should be taken into account when the study of emotion recognition abilities is targeted in its specificity.

On pleasure and thrill: the interplay between arousal and valence during visual word recognition

We investigated the interplay between arousal and valence in the early processing of affective words. Event-related potentials (ERPs) were recorded while participants read words organized in an orthogonal design with the factors valence (positive, negative, neutral) and arousal (low, medium, high) in a lexical decision task. We observed faster reaction times for words of positive valence and for those of high arousal. Data from ERPs showed increased early posterior negativity (EPN) suggesting improved visual processing of these conditions. Valence effects appeared for medium and low arousal and were absent for high arousal. Arousal effects were obtained for neutral and negative words but were absent for positive words. These results suggest independent contributions of arousal and valence at early attentional stages of processing. Arousal effects preceded valence effects in the ERP data suggesting that arousal serves as an early alert system preparing a subsequent evaluation in terms of valence.

Time pressure inhibits dynamic advantage in the classification of facial expressions of emotion

Recent studies suggest an advantage in the recognition of dynamic over static facial expressions of emotion. Here, we explored the differences in the processing of static and dynamic faces under condition of time pressure. A group of 18 participants classified static and dynamic facial expressions (angry, happy, and neutral). In order to increase the goal-directed attention, instructions emphasized speed and announced time pressure in the interval for the response (maximal 600 ms). Participants responded faster and more accurately in the static than in the dynamic condition. Event-related potentials (ERPs) showed larger amplitude of the P1 (90–130 ms) and LPC (300–600 ms) components for dynamic relative to static stimuli, indicating enhanced early visual processing and emotional attention. On the other hand, the N170 was more negative in static relative to dynamic faces, suggesting better structural encoding for static faces under time pressure. The present study shows some advantages in the processing of static over dynamic facial expressions of emotion when the top-down (goal-driven) attention is strengthened.

Facial EMG responses to emotional expressions are related to emotion perception ability

Although most people can identify facial expressions of emotions well, they still differ in this ability. According to embodied simulation theories understanding emotions of others is fostered by involuntarily mimicking the perceived expressions, causing a "reactivation" of the corresponding mental state. Some studies suggest automatic facial mimicry during expression viewing; however, findings on the relationship between mimicry and emotion perception abilities are equivocal. The present study investigated individual differences in emotion perception and its relationship to facial muscle responses - recorded with electromyogram (EMG)--in response to emotional facial expressions. N° = °269 participants completed multiple tasks measuring face and emotion perception. EMG recordings were taken from a subsample (N° = °110) in an independent emotion classification task of short videos displaying six emotions. Confirmatory factor analyses of the m. corrugator supercilii in response to angry, happy, sad, and neutral expressions showed that individual differences in corrugator activity can be separated into a general response to all faces and an emotion-related response. Structural equation modeling revealed a substantial relationship between the emotion-related response and emotion perception ability, providing evidence for the role of facial muscle activation in emotion perception from an individual differences perspective.

The Time Course of Emotion Effects in First and Second Language Processing: A Cross Cultural ERP Study with German-Spanish Bilinguals

To investigate whether second language processing is characterized by the same sensitivity to the emotional content of language - as compared to native language processing - we conducted an EEG study manipulating word emotional valence in a visual lexical decision task. Two groups of late bilinguals - native speakers of German and Spanish with sufficient proficiency in their respective second language - performed each a German and a Spanish version of the task containing identical semantic material: translations of words in the two languages. In contrast to theoretical proposals assuming attenuated emotionality of second language processing, a highly similar pattern of results was obtained across L1 and L2 processing: event related potential waves generally reflected an early posterior negativity plus a late positive complex for words with positive or negative valence compared to neutral words regardless of the respective test language and its L1 or L2 status. These results suggest that the coupling between cognition and emotion does not qualitatively differ between L1 and L2 although latencies of respective effects differed about 50-100 ms. Only Spanish native speakers currently living in the L2 country showed no effects for negative as compared to neutral words presented in L2 - potentially reflecting a predominant positivity bias in second language processing when currently being exposed to a new culture.

Effects of inter-stimulus interval on skin conductance responses and event-related potentials in a Go/NoGo task

Skin conductance responses (SCRs) to NoGo stimuli have been found to be smaller than to Go stimuli, possibly due to their diminished task relevance. These findings have been obtained at inter-stimulus intervals (ISI) that were unusually short for SCR recordings. Therefore, we tested whether the same findings would also hold at longer ISIs. Simultaneously, effects of ISI duration on the NoGo-N2 and-P3 components of event-related brain potentials (ERPs) were assessed. Go and NoGo stimuli were equiprobable while ISI varied between 2, 5, and 8s. Although increasing the ISI-enhanced SCR amplitudes in general, it did not modulate the attenuation of the response to NoGo relative to Go stimuli. When considered as difference between NoGo and Go conditions, neither the NoGo-N2 nor the NoGo-P3 was affected by ISI variation. Together, these data confirm the feasibility of co-registering ERPs and SCRs.