## 4 Discussion and Conclusions  
Self-face recognition holds a unique status in human social cognition [50, 51], possibly serving as the basis of indispensable functions such as empathy [52, 53]. Many people see their faces every day. However, the representation of self-face is known to be vulnerable to cognitive bias such as self-serving bias [8, 53, 54], which is demonstrated in several studies showing that people tend to select aesthetically enhanced versions of their face as the actual self-face [8]. The present study sought to clarify the neural basis of such a bias in self-face recognition by measuring ERPs elicited by original, aesthetically enhanced, and degraded versions of self and other familiar faces. Conventional analysis of ERP mean amplitude revealed larger P100 in the right than in the left occipital region. Although P100 is generally considered to reflect processing of low-level visual attributes such as luminance, this component is also reported to be sensitive to face-specific information [55, 56]. Taking this together with the oft-reported right-lateralization of face processing [57], presentation of facial stimuli might have enlarged P100 in the right hemisphere in the present study. A previous study [20] examined the influence of facial familiarity on early ERP components in the occipito-temporal region and found that N170 amplitude increases and P250 amplitude decreases as facial familiarity is higher. Our observation of larger P250 amplitude in response to other familiar versus self-face replicates their findings, which probably reflects the process of matching structural information of viewed faces with stored facial representations [19, 20]. In the present study, N170 amplitude was larger for self than other familiar faces, partially replicating the facial familiarity effect in [19], but puzzlingly, this trend was not observed for the original version. One plausible explanation for this null result is cultural differences. Many existing studies recruited participants from Western countries, whereas the participants of the current study were Japanese, where people accept collectivistic view [58], and familiar people are deemed as an extension of the self. Such collectivistic tendency might have blurred any differences in neural activations elicited by self and other familiar faces [59]. Another potential explanation is that the adaptation to the aesthetically manipulated version of self-face influenced processing of the original and aesthetically enhanced self-face. Recent studies using a serial dependence paradigm indicate that high-level adaptation to visual stimuli takes place after viewing an image just for a short duration [60, 61]. Unfortunately, the experimental design of the present study does not afford examination of perceptual adaptation and habituation effects on ERP components because a relatively small number of trials were conducted for an ERP study. However, it is conceivable that structural encoding stages of self and other faces as reflected in N170 [19, 20, 62] might have been modified by the repeated exposure to aesthetically manipulated faces. Multivariate analysis and cluster-based permutation statistics of ERP time series failed to detect statistically significant effects of facial identity in the N170 component, which indicates that a theory-driven approach of conventional analysis still has an edge over a data-driven approach in the analysis of early components. The sampling rate of the dataset was only 50 Hz, and the data from all the 61 channels were used in the multivariateanalysis. In contrast to this, data from occipto-temporal clusters sampled at 250 Hz were submitted to ERP mean amplitude analysis. One may conceive that such differences in datasets explain the failure of multivariate analysis to find any effects in early component. However, it is not the case at least in the present study.