Neural Responses to Perceptual and Sexual Ambiguity in Facial Images: An ERP and Time-Frequency Analysis

This study investigated the neural effects of perceptual (caused by blur processing) and sexual ambiguity (induced by morphing manipulation) in facial images via event-related potentials (ERPs) and time-frequency analysis. Gaussian blur and morphing of male and female faces were used to create gradually ambiguous face images, and participants completed a sexual dimorphism judgment task. Results revealed that the N170 was strongly affected by blur, which suggested that it disrupted the structural encoding of faces. The EPN exhibited a different response compared with the N170, which indicated that it may reflect both bottom-up processing due to lack of visual cues and top-down processing driven by the sexual dimorphism judgment task. Additionally, LPP amplitude increased under conditions of explicit perceptual and sexual faces, which confirmed that ease of interpretation in sexual dimorphism judgments influenced neural responses. Furthermore, the time-frequency analysis revealed that high-frequency gamma activity at approximately 200 ms was associated with extracting and evaluating facial features, whereas activity after 600 ms reflected processes related to retaining facial information. These findings suggest that visual processing and semantic evaluation of faces rely on complex mechanisms influenced by both the clarity of physical cues and task context.