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.

Dynamic human and avatar facial expressions elicit differential brain responses.

Computer-generated characters, so-called avatars, are widely used in advertising, entertainment, human-computer interaction or as research tools to investigate human emotion perception. However, brain responses to avatar and human faces have scarcely been studied to date. As such, it remains unclear whether dynamic facial expressions of avatars evoke different brain responses than dynamic facial expressions of humans. In this study, we designed anthropomorphic avatars animated with motion tracking and tested whether the human brain processes fearful and neutral expressions in human and avatar faces differently. Our fMRI results showed that fearful human expressions evoked stronger responses than fearful avatar expressions in the ventral anterior and posterior cingulate gyrus, the anterior insula, the anterior and posterior superior temporal sulcus, and the inferior frontal gyrus. Fearful expressions in human and avatar faces evoked similar responses in the amygdala. We did not find different responses to neutral human and avatar expressions. Our results highlight differences, but also similarities in the processing of fearful human expressions and fearful avatar expressions even if they are designed to be highly anthropomorphic and animated with motion tracking. This has important consequences for research using dynamic avatars, especially when processes are investigated that involve cortical and subcortical regions.

Dynamics and diversity of heart rate responses to a disaster motion picture.

Emotions are dynamic neuropsychophysiological processes that guide behavior and serve as crucial signals during social interactions. Measuring their highly individual temporal dynamics is an unresolved challenge, but the coupling of autonomic and central nervous processes offers a promising approach. We present a feasible approach to study changes in heart rate during emotions and demonstrate a link to empathy. We investigated the interindividual similarity and temporal dynamics of heart rate responses to an emotive motion picture. Forty healthy participants watched "The Impossible" (109 min; Hermida Muñiz et al., 2012) while their heart rate was recorded. Interindividual concordance of heart rate responses was analysed using agglomerative hierarchical clustering analyses to distinguish response patterns throughout the movie and during six highly emotive scenes. This revealed multiple response patterns during emotive scenes. Second, we analysed how changes in heart rate are linked to self-reported empathy. We found that the extent of changes in heart rate is positively linked to trait and state empathy. During specific scenes, this relationship was only visible when individuals with homogeneous heart rate response patterns were observed, but not across discordant response patterns. In conclusion, our results demonstrate that heart rate responses to complex social stimuli are not uniform. Therefore, research should favour statistical procedures with the potential to detect interindividual differences. The approach presented in our study allows us to depict interindividual similarity and diversity in emotional autonomic responses and emphasizes the key role of empathy in emotional experiences.