Double dissociation of configural and featural face processing on P1 and P2 components as a function of spatial attention

The Neural Mechanisms of Group Membership Effect on Emotional Mimicry: A Multimodal Study Combining Electromyography and Electroencephalography

Emotional mimicry plays a vital role in understanding others' emotions and has been found to be modulated by social contexts, especially group membership. However, the neural mechanisms underlying this modulation remain unclear. We explored whether and how group membership modulated emotional mimicry using a multimodal method combining facial electromyography (fEMG) and electroencephalography (EEG). We instructed participants to passively view dynamic emotional faces (happy vs. angry) of others (in-group vs. out-group) and simultaneously recorded their fEMG and EEG responses. Then, we conducted combined analyses of fEMG-EEG by splitting the EEG trials into two mimicry intensity categories (high-intensity mimicry vs. low-intensity mimicry) according to fEMG activity. The fEMG results confirmed the occurrence of emotional mimicry in the present study but failed to find a group membership effect. However, the EEG results showed that participants mimicked in-group happiness and anger more than out-group. Importantly, this in-group preference involved different neural mechanisms in happiness and anger mimicry. In-group preference for happiness mimicry occurred at multiple neural mechanisms such as N1 (at P7, Pz, and P8), P2 (at Pz and P8), N2 (at P8), and P3 (at P7, Pz, and P8); in-group preference for anger mimicry occurred at P1 (at P7) and P2 (at Pz). Our findings provide new neural evidence for the effect of group membership on emotional mimicry by uncovering the temporal dynamics of this effect.

Face motion form at learning influences the time course of face spatial frequency processing during test

Studies that use static faces suggest that facial processing follows a coarse-to-fine sequence; i.e., holistic precedes featural processing, due to low and high spatial frequencies (LSF, HSF) transmitting holistic/global and featural/local information respectively. Although recent studies have focused on the role of facial movement in holistic facial processing, it is unclear whether moving faces have the same processing mechanism as static ones, especially in the time course of processing. The current study uses the event-related potential technique to investigate this issue by manipulating the facial format at study and face spatial frequency during the test. ERP results showed that the P1 amplitude was increased by LSF faces relative to HSF ones, using both moving and static study faces, with the former larger than the latter. The N170 amplitude was more sensitive to HSF than LSF faces when only static study faces were used, while the P2 amplitude was more sensitive to LSF faces regardless of the facial study format. The above results were not modulated by the race of the faces. These results favor the view that regardless of face race, moving study faces promote holistic processing during the earliest stage of face recognition. Furthermore, holistic processing is observed to be the same for both static and moving study faces at a later stage associated with more in-depth processing. It is evident that facial motion should be factored into further studies of face recognition, given the distinctions between holistic and featural processing for moving and static study faces.

The Time Sequence of Face Spatial Frequency Differs During Working Memory Encoding and Retrieval Stages

Previous studies have found that P1 and P2 components were more sensitive to configural and featural face processing, respectively, when attentional resources were sufficient, suggesting that face processing follows a coarse-to-fine sequence. However, the role of working memory (WM) load in the time course of configural and featural face processing is poorly understood, especially whether it differs during encoding and retrieval stages. This study employed a delayed recognition task with varying WM load and face spatial frequency (SF). Our behavioral and ERP results showed that WM load modulated face SF processing. Specifically, for the encoding stage, P1 and P2 were more sensitive to broadband SF (BSF) faces, while N170 was more sensitive to low SF (LSF) and BSF faces. For the retrieval stage, P1 on the right hemisphere was more sensitive to BSF faces relative to HSF faces, N170 was more sensitive to LSF faces than HSF faces, especially under the load 1 condition, while P2 was more sensitive to high SF (HSF) faces than HSF faces, especially under load 3 condition. These results indicate that faces are perceived less finely during the encoding stage, whereas face perception follows a coarse-to-fine sequence during the retrieval stage, which is influenced by WM load. The coarse and fine information were processed especially under the low and high load conditions, respectively.

Configural but Not Featural Face Information Is Associated With Automatic Processing

Configural face processing precedes featural face processing under the face-attended condition, but their temporal sequence in the absence of attention is unclear. The present study investigated this issue by recording visual mismatch negativity (vMMN), which indicates the automatic processing of visual information under unattended conditions. Participants performed a central cross size change detection task, in which random sequences of faces were presented peripherally, in an oddball paradigm. In Experiment 1, configural and featural faces (deviant stimuli) were presented infrequently among original faces (standard stimuli). In Experiment 2, configural faces were presented infrequently among featural faces, or vice versa. The occipital-temporal vMMN emerged in the 200–360 ms latency range for configural, but not featural, face information. More specifically, configural face information elicited a substantial vMMN component in the 200–360 ms range in Experiment 1. This result was replicated in the 320–360 ms range in Experiment 2, especially in the right hemisphere. These results suggest that configural, but not featural, face information is associated with automatic processing and provides new electrophysiological evidence for the different mechanisms underlying configural and featural face processing under unattended conditions.

The spatiotemporal characteristics of N170s for faces and words: A meta-analysis study

N170 is a negative event-related potential (ERP) component in response to visual stimuli, such as faces. It remains controversial whether N170 reflects the specific processing of faces or can also be elicited by objects of expertise (e.g., words). In this research, we conducted a meta-analysis for the spatiotemporal characteristics of N170 of face and word stimuli from 24 studies in which both stimuli were presented for each subject. We observed that (1) both face and word stimuli can elicit conspicuous N170s and that there was no difference between the amplitude of face-N170 and word-N170; (2) there is no difference in the latencies between the two N170s; and (3) both N170s are distributed in the occipitotemporal regions but with a reversed hemispheric distribution pattern-face-N170 is more negative in the right than left occipitotemporal regions, while word-N170 is the opposite. These results showed that the face- and word-N170s are qualitatively the same but have different hemispheric lateralization advantages-N170 might be a general neural index of the expertise-dependent object-recognition process in occipitotemporal regions.

Cultural Differences in the Time Course of Configural and Featural Processing for Own-race Faces

Previous research suggests that East Asians pay more attention than Caucasian Westerners to configural information in faces, while the latter group pays more attention to featural information. However, it is unclear whether this cultural variation in attention produces a different time course of the processing bias for configural and featural information. This was examined using event-related potentials in a spatial attention paradigm. Chinese and Westerners were instructed to attend to the locations of two face images or houses. Although the race-related difference was absent in behavioral performance and N170 component, Chinese participants exhibited a configural processing bias on P1 component in the case of both own- and other-race faces and a featural processing bias on P2 component for own-race faces. In contrast, Westerners exhibited a featural processing bias for own-race faces and a configural processing bias for other-race faces on P1 component, whereas a configural processing bias was observed on P2 component for both own- and other-race faces. These results demonstrate that there are important differences between East Asians and Westerners in their relative preferences for configural versus featural processing of own-race faces, but not other-race faces. The relative roles of configural and featural information processing for faces are thus dependent on both who is looking (the culture or race of the observer) and what they are looking at (the race of the face): Easterners enjoy an early global/configural processing bias and a late local/featural processing bias for own-race faces, while Westerners benefit from an early local/featural processing bias and a late global/configural processing bias for own-race faces; both of the groups have an early and late global/configural processing bias for other-race faces.

Early and late cortical responses to directly gazing faces are task dependent

Gender categorisation of human faces is facilitated when gaze is directed toward the observer (i.e., a direct gaze), compared with situations where gaze is averted or the eyes are closed (Macrae, Hood, Milne, Rowe, & Mason, Psychological Science, 13(5), 460-464, 2002). However, the temporal dynamics underlying this phenomenon remain to some extent unknown. Here, we used electroencephalography (EEG) to assess the neural correlates of this effect, focusing on the event-related potential (ERP) components known to be sensitive to gaze perception (i.e., P1, N170, and P3b). We first replicated the seminal findings of Macrae et al. (2002, Experiment 1) regarding facilitated gender discrimination, and subsequently measured the underlying neural responses. Our data revealed an early preferential processing of direct gaze as compared with averted gaze and closed eyes at the P1, which reverberated at the P3b (Experiment 2). Critically, using the same material, we failed to reproduce these effects when gender categorisation was not required (Experiment 3). Taken together, our data confirm that direct gaze enhances the early P1, as well as later cortical responses to face processing, although the effect appears to be task dependent.

Spatial attention modulates the temporal sequence of hemispheric asymmetry in configural and featural face processing

Face recognition requires both configural and featural processing. Configural face processing is more dependent on the right hemisphere, whereas featural face processing is more dependent on the left hemisphere. The ERP components sensitive to configural and featural face processing were found on P1 and P2, respectively. However, whether lateralized processing is independent of or interacts with the temporal sequence of configural and featural face processing is unclear. To prevent potentially confounding physical stimuli differences between configural and featural face processing from affecting the ERP components, a spatial attention paradigm was employed in which the participants were instructed to attend to the face location (the attended face condition) or the house location (the unattended face condition). The interaction effect of attention, face processing type and hemisphere on the P1 and P2 components indicates that the different mechanisms of configural and featural face processing are a function of spatial attention. Specifically, under the attended face condition, the posterior P1 (approximately 100 ms) for configural face processing was larger than that for featural face processing in the right hemisphere, whereas the P2 (approximately 220 ms) for featural face processing was larger than that for configural face processing in the left hemisphere. In contrast, under the unattended face condition, the P1 for featural face processing was larger than that for configural face processing in the left hemisphere, whereas the P2 for configural face processing was larger than that for featural face processing in the right hemisphere. Therefore, configural and featural processing involve different neural mechanisms, and more importantly, the time course of hemispheric asymmetry in configural and featural face processing is differentially modulated by spatial attention.

N170 Reveals the Categorical Perception Effect of Emotional Valence

As an important attribute of facial expression, emotional valence has been well explored, but its processing mechanisms remain ambiguous. Investigating the categorical perception (CP) of emotional valence might help uncover the objective basis of the subjective dichotomy of emotional valence and identify the stage at which this processing of valence information might occur. A judgment task was used in the current study with stimuli from the within- or between-category condition, in which participants were required to decide whether two presented faces showed the same emotion. The results of the behavioral experiment revealed a significant CP effect of emotional valence, with faster RTs and greater accuracy for the between- than for the within-category stimuli. In the ERP experiment, the N170 (peaking at approximately 150-170 ms) was found to reflect the CP effect of emotional valence, with a larger amplitude for the within- than for the between-category condition. In contrast, the P1 component (peaking at approximately 100-130 ms) was insensitive to the CP effect of emotional valence. These results reveal the existence of the CP of emotional valence and indicate that the N170 is its earliest electrophysiological index. Therefore, the categorization of emotional valence not only has an objective neural basis but occurs at a relatively early stage of processing.

Relative expertise affects N170 during selective attention to superimposed face-character images

It remains unclear whether the N170 of ERPs reflects domain-specific or domain-general visual object processing. In this study, we used superimposed images of a face and a Chinese character such that participants' relative expertise for the two object types was either similar (Experiment 1 and 2) or different (Experiment 3). Experiment 1 showed that N170 amplitude was larger when participants attended to the character instead of the face of a face-character combination. This result was unchanged in Experiment 2, in which task difficulty was selectively increased for the face component of the combined stimuli. Experiment 3 showed that, although this N170 enhancement for attending to characters relative to faces persisted for false characters with recognizable parts, it disappeared for unrecognizable characters. Therefore, N170 amplitude was significantly greater for Chinese characters than for faces presented within a combined image, independent of the relative task difficulty. This result strongly calls N170 face selectivity into question, demonstrating that, contrary to the expectations established by a domain-specific account, N170 is modulated by expertise.