Detecting brief changes of facial expression is vital for social communication. Yet, how reliably, how fast these changes are detected and how long they are processed in the human brain remain unknown. High-density electroencephalogram (EEG) was recorded in 18 participants presented with a neutral-expression face at a rate of 5.88 Hz (F) for 80 s. Every five faces, the face changed expression to fear, disgust or happiness (different stimulation sequences). The resulting 1.18 Hz (F/5) EEG response and its harmonics objectively indexed detection of a brief change of facial expression. This response was recorded in every participant in a few minutes but was largely reduced for inverted faces, indicating that it reflects high-level processes. Although this response focused on occipito-temporal sites, different expression changes evoked reliably distinct topographical maps, pointing to partly distinct neural generators. These effects were also observed at a faster 12 Hz frequency rate and a lower ratio of expression change (1/9). Time-domain analysis showed that a brief change of expression inserted in a dynamic stimulation sequence elicits specific occipito-temporal responses between 100 and 310 ms, indicating a rapid change detection process followed by a long integration period of facial expression information in the human brain.

Sexual dimorphism in physical appearance may be an important cue in both intra-and inter-sex competition. Recently, the facial width-to-height ratio (fWHR) has been proposed as a novel sexually dimorphic morphologic measure, with men suggested to have a higher fWHR than women. Currently, however, the status of fWHR as a sexually dimorphic trait is unclear. Here we tested for sexual dimorphism in fWHR, as well as in three additional, previously reported, facial measures, in four (three Caucasian and one African) independent samples. In three of the four samples, no significant sex differences in fWHR were observed. In one sample males showed a significantly lower (rather than higher) fWHR than females (this effect was no longer significant after controlling for Body Mass Index). By contrast, significant and large sex differences were observed in all four samples for each of the three previously validated facial metrics; namely: (i) lower face/face height, (ii) cheekbone prominence, and (iii) face width/lower face height. These results provide strong evidence against the claim that fWHR, at least as measured from the surface of the face, is sexually dimorphic.

BackgroundThe human brain is frequently exposed to individual faces across a wide range of different apparent sizes, often seen simultaneously (e.g., when facing a crowd). Here we used a sensitive and objective fast periodic visual stimulation approach while recording scalp electroencephalogram (EEG) to test the effect of size variation on neural responses reflecting individual face discrimination.MethodsEEG was recorded in ten observers presented with the same face identity at a fixed rate (5.88 Hz, frequency F) and different oddball face identities appearing every five faces (F/5, i.e., 1.18 Hz). Stimulus size was either constant (6.5 × 4 degrees of visual angle) or changed randomly at each stimulation cycle, by 2:1 ratio increasing values from 10% to 80% size variation in four conditions. Absolute stimulus size remained constant across conditions.ResultsThe base rate 5.88 Hz EEG response increased with image size variation, particularly over the right occipito-temporal cortex. In contrast, size variation decreased the oddball response marking individual face discrimination over the right occipito-temporal cortex. At constant stimulus size, the F/5 change of identity generated an early (about 100 ms) oddball response reflecting individual face discrimination based on image-based cues. This early component disappeared with a relatively small size variation (i.e., 20%), leaving a robust high-level index of individual face discrimination.ConclusionsStimulus size variation is an important manipulation to isolate the contribution of high-level visual processes to individual face discrimination. Nevertheless, even for relatively small stimuli, high-level individual face discrimination processes in the right occipito-temporal cortex remain sensitive to stimulus size variation.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2202-15-87) contains supplementary material, which is available to authorized users.

This study explored the extent to which there are the neural correlates of the affective personality influence on face processing using event-related potentials (ERPs). In the learning phase, participants viewed a target individual’s face (expression neutral or faint smile) paired with either negative, neutral or positive sentences describing previous typical behavior of the target. In the following EEG testing phase, participants completed gender judgments of the learned faces. Statistical analyses were conducted on measures of neural activity during the gender judgment task. Repeated measures ANOVA of ERP data showed that faces described as having a negative personality elicited larger N170 than did those with a neutral or positive description. The early posterior negativity (EPN) showed the same result pattern, with larger amplitudes for faces paired with negative personality than for others. The size of the late positive potential was larger for faces paired with positive personality than for those with neutral and negative personality. The current study indicates that affective personality information is associated with an automatic, top–down modulation on face processing.

BackgroundIndividuals with autism spectrum disorder (ASD) are characterized by impairments in social communication and interaction. Although difficulties at processing social signals from the face in ASD have been observed and emphasized for many years, there is a lot of inconsistency across both behavioral and neural studies.MethodsWe recorded scalp electroencephalography (EEG) in 23 8-to-12 year old boys with ASD and 23 matched typically developing boys using a fast periodic visual stimulation (FPVS) paradigm, providing objective (i.e., frequency-tagged), fast (i.e., few minutes) and highly sensitive measures of rapid face categorization, without requiring any explicit face processing task. We tested both the sensitivity to rapidly (i.e., at a glance) categorize faces among other objects and to individuate unfamiliar faces.OutcomesWhile general neural synchronization to the visual stimulation and neural responses indexing generic face categorization were undistinguishable between children with ASD and typically developing controls, neural responses indexing individual face discrimination over the occipito-temporal cortex were substantially reduced in the individuals with ASD. This difference vanished when faces were presented upside-down, due to the lack of significant face inversion effect in ASD.InterpretationThese data provide original evidence for a selective high-level impairment in individual face discrimination in ASD in an implicit task. The objective and rapid assessment of this function opens new perspectives for ASD diagnosis in clinical settings.