The N170 Is Linked to Configural Face Processing: Evidence From the N170 Adaptation Effect for Upright Faces

Although the N170 component is popularly regarded as a marker of configural face processing, contradictory evidence exists. Many neural adaptation studies employing upright and inverted faces as adaptor and test stimuli have reported N170 adaptation effects (i.e., amplitude reduction when preceded by the same versus different face orientation) for inverted but not upright faces, suggesting N170's sensitivity to featural rather than configural processing. Noting that most prior studies relied on non-face-related tasks, the present study systematically investigated N170 adaptation effects under different tasks. Consistent with previous findings, we did not observe a significant adaptation effect for upright faces during a non-face task (flower detection), but such effects emerged in tasks requiring active face discrimination (repeated or target face detection). By contrast, adaptation effects for inverted faces were present regardless of task. Notably, all adaptation effects persisted despite changes in face identity, image, or size, and consistently exhibited the typical right occipito-temporal distribution associated with face processing, indicating they are not attributable to low-level visual adaptation. Further analysis revealed that the N170 adaptation effect for upright faces was influenced by variation in face image but not size, with strongest effects observed when consecutive faces shared the same identity and photograph, an effect absent for inverted faces. Together, our findings suggest that distinct neuronal populations underlie the N170: those more sensitive to inverted faces may process salient facial features (e.g., eyes), while those tuned to upright faces are engaged in configural processing and high-level analysis of facial image patterns.