Neurophysiological correlates for the perception of facial sexual dimorphism

An ecological measure of rapid and automatic face-sex categorization

Sex categorization is essential for mate choice and social interactions in many animal species. In humans, sex categorization is readily performed from the face. However, clear neural markers of face-sex categorization, i.e., common responses to widely variable individuals from one sex, have not been identified so far in humans. To isolate a direct signature of rapid and automatic face-sex categorization generalized across a wide range of variable exemplars, we recorded scalp electroencephalogram (EEG) from 32 participants (16 females) while they were exposed to variable natural face images from one sex alternating at a rapid rate of 6 Hz (i.e., 6 images per second). Images from the other sex were inserted every 6th stimulus (i.e., at a 1-Hz rate). A robust categorization response to both sex contrasts emerged at 1 Hz and harmonics in the EEG frequency spectrum over the occipito-temporal cortex of most participants. The response was larger for female faces presented among male faces than the reverse, suggesting that the two sex categories are not equally homogenous. This asymmetrical response pattern disappeared for upside-down faces, ruling out the contribution of low-level physical variability across images. Overall, these observations demonstrate that sex categorization occurs automatically after a single glance at natural face images and can be objectively isolated and quantified in the human brain within a few minutes.

Event-related potentials modulated by the perception of sexual dimorphism: The influence of attractiveness and sex of faces

Sexual dimorphism has been proposed as one of the facial traits to have evolved through sexual selection and to affect attractiveness perception. Even with numerous studies documenting its effect on attractiveness and mate choice, the neurophysiological correlates of the perception of sexual dimorphism are not yet fully understood. In the present study, event-related potentials (ERPs) were recorded during visualisation of faces that had been previously transformed in shape to appear more masculine or more feminine. The participants' task consisted of judging the attractiveness of half of the total number of faces, and performing a sex discrimination task on the other half. Both early and late potentials were modulated by the sex of faces, whereas the effect of the sexually dimorphic transform was mainly visible in the P2 (positive deflection around 200 ms after stimulus onset), EPN (early posterior negativity) and LPP (late positive potential) components. There was an effect of sexual dimorphism on P2 and EPN amplitudes when female participants visualised male faces, which may indicate that masculinity is particularly attended to when viewing opposite sex members. Also, ERP results seem to support the idea of sex differences in social categorisation decisions regarding faces, although differences were not evident on behavioural results. In general, these findings contribute to a better understanding of how humans perceive sexually dimorphic characteristics in other individuals' faces and how they affect attractiveness judgements.

In search of biomarkers in psychiatry: EEG-based measures of brain function

Current clinical parameters used for diagnosis and phenotypic definitions of psychopathology are both highly variable and subjective. Intensive research efforts for specific and sensitive biological markers, or biomarkers, for psychopathology as objective alternatives to the current paradigm are ongoing. While biomarker research in psychiatry has focused largely on functional neuroimaging methods for identifying the neural functions that associate with psychopathology, scalp electroencephalography (EEG) has been viewed, historically, as offering little specific brain source information, as scalp appearance is only loosely correlated to its brain source dynamics. However, ongoing advances in signal processing of EEG data can now deliver functional EEG brain-imaging with distinctly improved spatial, as well as fine temporal, resolution. One computational approach proving particularly useful for EEG cortical brain imaging is independent component analysis (ICA). ICA decomposition can be used to identify distinct cortical source activities that are sensitive and specific to the pathophysiology of psychiatric disorders. Given its practical research advantages, relatively low cost, and ease of use, EEG-imaging is now both feasible and attractive, in particular for studies involving the large samples required by genetically informative designs to characterize causal pathways to psychopathology. The completely non-invasive nature of EEG data acquisition, coupled with ongoing advances in dry, wireless, and wearable EEG technology, makes EEG-imaging increasingly attractive and appropriate for psychiatric research, including the study of developmentally young samples. Applied to large genetically and developmentally informative samples, EEG imaging can advance the search for robust diagnostic biomarkers and phenotypes in psychiatry.

Attention, response inhibition, and face-information processing in children: the role of task characteristics, age, and gender

The aim of the study was to assess: (a) developmental changes in attention, response inhibition, and face-information processing using the new Balloons task and (b) to evaluate the association between measures derived from the task with reported behavior problems. One hundred and thirty-four typically developing children (53 boys and 81 girls) were tested with the Balloons. Their parents and teachers completed the Child Behavior Checklist. Our results validate the Balloons as a reliable task with significant effects of manipulations in difficulty level (speed, processing load, and processing type). The results suggest that face-information processing undergoes significant changes during the age period between 7 and 13 years with significant gender differences. Modest but significant correlations were found between the Balloons' measures and behavior problems.