Abstract
Human faces look more similar to each other when they are presented upside-down, leading to an increase of error rate and response time during individual face discrimination tasks. This inversion effect is one of the most robust finding in the face processing literature. Recent neuroimaging studies using adaptation to face identity have shown that the ‘fusiform face area’ was the primary neural source of the behavioral face inversion effect (FIE). However, the time course of the FIE - i.e. when inversion affects the coding of facial identity in the human brain - remains unclear. Here we addressed this question by recording event-related potentials (ERPs) on the scalp during an adaptation paradigm with upright and inverted faces. Subjects were presented with a first (adapting) face stimulus for about 3000 ms, followed by a second face of either the same identity or a different identity. The ERP response to the second face stimulus was markedly reduced over occipito-temporal electrode sites when it was identical to the adapting face, starting at about 160 ms. When the exact same stimuli were presented upside-down, the reduction of signal was smaller, and took place about 30 ms later, in line with the behavioral effect of inversion. This result shows that the effect of face inversion on individual face discrimination takes place during early face perceptual processes in the occipito-temporal cortex. It also strongly suggests that individual face configuration is extracted as early as 160 ms following stimulus onset.
Authors are supported by the Belgian National Foundation for Scientific Research (FNRS)