Asymmetries in event-related potentials part 1: A systematic review of face processing studies

The human brain shows distinct lateralized activation patterns for a range of cognitive processes. One such function, which is thought to be lateralized to the right hemisphere (RH), is human face processing. Its importance for social communication and interaction has led to a plethora of studies investigating face processing in health and disease. Temporally highly resolved methods, like event-related potentials (ERPs), allow for a detailed characterization of different processing stages and their specific lateralization patterns. This systematic review aimed at disentangling some of the contradictory findings regarding the RH specialization in face processing focusing on ERP research in healthy participants. Two databases were searched for studies that investigated left and right electrodes while participants viewed (mostly neutral) facial stimuli. The included studies used a variety of different tasks, which ranged from passive viewing to memorizing faces. The final data selection highlights, that strongest lateralization to the RH was found for the N170, especially for right-handed young male participants. Left-handed, female, and older participants showed less consistent lateralization patterns. Other ERP components like the P1, P2, N2, P3, and the N400 were overall less clearly lateralized. The current review highlights that many of the assumed lateralization patterns are less clear than previously thought and that the variety of stimuli, tasks, and EEG setups used, might contribute to the ambiguous findings.

Impaired inhibitory control when processing real but not cartoon emotional faces in autistic children: Evidence from an event-related potential study

Impaired socioemotional functioning characterizes autistic children, but does weak inhibition control underlie their socioemotional difficulty? This study addressed this question by examining whether and, if so, how inhibition control is affected by face realism and emotional valence in school-age autistic and neurotypical children. Fifty-two autistic and 52 age-matched neurotypical controls aged 10-12 years completed real and cartoon emotional face Go/Nogo tasks while event-related potentials (ERPs) were recorded. The analyses of inhibition-emotion components (i.e., N2, P3, and LPP) and a face-specific N170 revealed that autistic children elicited greater N2 while inhibiting Nogo trials and greater P3/LPP and late LPP for real but not cartoon emotional faces. Moreover, autistic children exhibited a reduced N170 to real face emotions only. Furthermore, correlation results showed that better behavioral inhibition and emotion recognition in autistic children were associated with a reduced N170. These findings suggest that neural mechanisms of inhibitory control in autistic children are less efficient and more disrupted during real face processing, which may affect their age-appropriate socio-emotional development.

Do perceptual expertise and implicit racial bias predict early face-sensitive ERP responses?

Studies examining the visual perception of face race have revealed mixed findings regarding the presence or direction of effects on early face-sensitive event-related potential (ERP) components. Few studies have examined how early ERP components are influenced by individual differences in bottom-up and top-down processes involved in face perception, and how such factors might interact to influence early face-sensitive ERP components has yet to be investigated. Thus, the current study examined whether P100, N170, and P200 responses can be predicted by individual differences in own- and other-race face recognition, implicit racial bias, and their interaction. Race effects were observed in the P100, N170, and P200 responses. Other-race face recognition, implicit racial biases, and their interaction explained a significant amount of unique variability in N170 responses when viewing other-race faces. Responses to own-race faces were minimally influenced with only implicit racial bias predicting a significant amount of unique variability in N170 latency when viewing own-race faces. Face recognition, implicit racial bias, or their interaction did not predict P100 responses. The current findings suggest that face recognition abilities and its interaction with implicit racial bias modulate the early stages of other-race face processing.

Differential effects of face-realism and emotion on event-related brain potentials and their implications for the uncanny valley theory

Cartoon characters are omnipresent in popular media. While few studies have scientifically investigated their processing, in computer graphics, efforts are made to increase realism. Yet, close approximations of reality have been suggested to evoke sometimes a feeling of eeriness, the “uncanny valley” effect. Here, we used high-density electroencephalography to investigate brain responses to professionally stylized happy, angry, and neutral character faces. We employed six face-stylization levels varying from abstract to realistic and investigated the N170, early posterior negativity (EPN), and late positive potential (LPP) event-related components. The face-specific N170 showed a u-shaped modulation, with stronger reactions towards both most abstract and most realistic compared to medium-stylized faces. For abstract faces, N170 was generated more occipitally than for real faces, implying stronger reliance on structural processing. Although emotional faces elicited highest amplitudes on both N170 and EPN, on the N170 realism and expression interacted. Finally, LPP increased linearly with face realism, reflecting activity increase in visual and parietal cortex for more realistic faces. Results reveal differential effects of face stylization on distinct face processing stages and suggest a perceptual basis to the uncanny valley hypothesis. They are discussed in relation to face perception, media design, and computer graphics.

Human Empathy, Personality and Experience Affect the Emotion Ratings of Dog and Human Facial Expressions

Facial expressions are important for humans in communicating emotions to the conspecifics and enhancing interpersonal understanding. Many muscles producing facial expressions in humans are also found in domestic dogs, but little is known about how humans perceive dog facial expressions, and which psychological factors influence people’s perceptions. Here, we asked 34 observers to rate the valence, arousal, and the six basic emotions (happiness, sadness, surprise, disgust, fear, and anger/aggressiveness) from images of human and dog faces with Pleasant, Neutral and Threatening expressions. We investigated how the subjects’ personality (the Big Five Inventory), empathy (Interpersonal Reactivity Index) and experience of dog behavior affect the ratings of dog and human faces. Ratings of both species followed similar general patterns: human subjects classified dog facial expressions from pleasant to threatening very similarly to human facial expressions. Subjects with higher emotional empathy evaluated Threatening faces of both species as more negative in valence and higher in anger/aggressiveness. More empathetic subjects also rated the happiness of Pleasant humans but not dogs higher, and they were quicker in their valence judgments of Pleasant human, Threatening human and Threatening dog faces. Experience with dogs correlated positively with ratings of Pleasant and Neutral dog faces. Personality also had a minor effect on the ratings of Pleasant and Neutral faces in both species. The results imply that humans perceive human and dog facial expression in a similar manner, and the perception of both species is influenced by psychological factors of the evaluators. Especially empathy affects both the speed and intensity of rating dogs’ emotional facial expressions.

Attentional Modulation of the Emotional Expression Processing Studied with ERPs and sLORETA

Recent ERP studies demonstrate that the processing of facial emotional expression can be modulated by attention. The aim of the present study was to investigate the neural correlates of attentional influence on the emotional expression processing at early stages. We recorded ERP responses to facial stimuli containing neutral versus emotional expression in two different conditions. The first task was to discriminate facial expressions, while the second task was to categorize face gender. Enhanced positivity at occipital and occipito-temporal locations between 110 and 170 ms poststimulus was elicited by facial stimuli presented in the expression task when compared to the gender task. This effect temporally overlapped with the P1 and N170 components, which reflect the early stages of face processing. To localize the sources of the brain activity underlying observed attentional modulation, we used Standardized Low Resolution Electromagnetic Tomography. Enhanced activity within the extrastriate cortex for the expression task was obtained as the reflection of early ERP effect. Additionally, we found stronger activation within the superior temporal and the fusiform gyrus of the right hemisphere in the expression task when compared to the gender task. Our findings undoubtedly confirm that early stages of the emotional expression processing can be modified by top-down attention.