RESUMO
The present electroencephalography (EEG) study observed how the brain processes visual stimuli (words and shapes) displayed with four different duration times (17 ms, 33 ms, 67 ms, and 100 ms). All stimuli had to be classified into "I saw nothing", "I saw a blur", "I saw a word," or "I saw a shape" via distinct button presses while brain potentials were being measured. The neurophysiological correlates of word and shape processing were subsequently analysed and compared for two distinct time points at the occipito-parietal area in both hemispheres (P7 and P8). In a further step, word and shape identification rates were also analysed. Identification rates revealed that participants recognized words and shapes when presented for 17 ms at a rate of only 6% and 7%, which is poor enough to assume an overall lack of conscious recognition. Analysis of EEG data revealed two time points of interest, one at 210 ms and the other at 280 ms post stimulus onset. Brain potentials at the earlier time point reflect modulations in presentation duration with increased amplitudes elicited by longer presentations. At this time point, no differences were seen between words and shapes in both hemispheres. The later time point, though, clearly distinguished between word and shape processing with totally missing amplitudes (i.e., brain activity) in the case of shapes in general in both hemispheres. Crucially, words presented for only 17 ms still elicited an average brain potential amplitude significantly different from the corresponding 17 ms presentations of shapes at this time point at electrode location P7, even though both stimuli categories were basically not seen (i.e., not consciously recognized). This later word-specific brain potential for the shortest presentation duration is interpreted as neurophysiological evidence of subliminal word processing. Strikingly, this difference was not found in the right hemisphere at P8.
RESUMO
The aim of this study was to investigate how a female face is perceived in terms of its attractiveness, dominance, health, femininity-masculinity, and maturity in direct relation to the body fat percentage (BFP) conveyed by the face. To compare how young adults (ages 18 to 35) respond to different levels of body fat percentage both subjectively and objectively we collected survey ratings and electroencephalography (EEG) data across five different levels of BFP from 40 participants. We adapted the experimental design from a prior behavioral study and used calibrated and morphed female face images of five different BFP levels. The results of the survey are in consensus with the previous study and assessed to be a successful replication. From the EEG data, event-related potentials (ERPs) were extracted from one electrode location (right occipitotemporal brain region) known to be particularly sensitive to face-stimuli. We found statistically significant differences in the amplitudes of the P200 component (194 ms post stimulus onset) between the thickest face and all four other BFP conditions, and in the amplitudes of the N300 component (274 ms post stimulus onset) between the average face and three other BFP conditions. As expected, there were no significant differences among the N170 amplitudes of all five BFP conditions since this ERP component simply reflects the processing of faces in general. From these results, we can infer that holistic face encoding characterized by the N170 component in the right occipitotemporal area is followed by serial evaluative processes, whose categorical and qualitative matrix and spatiotemporal dynamics should be further explored in future studies, especially in relation to the social constructs that were focused on in this study.
