Face inversion does not affect the information content coded during the N170

Abstract

Abstract Face inversion dramatically disrupts our ability to process faces, which is known as the face inversion effect. Previous electrophysiological studies have indicated that the N170 ERP component is delayed and sometimes larger in response to inverted compared to upright faces. However, the nature of these effects remains elusive because we do not yet understand the information coding function of the N170 in upright and inverted faces. Here, we assessed what facial information the N170 codes and when it does so for upright and inverted faces. To this aim, we used one of the simplest socially relevant tasks: face detection. In this task, 10 healthy adults (5 females, median age=23, 20-29) saw pictures of faces and noise textures revealed through ten small Gaussian apertures (bubbles). Participants performed two sessions of trials with upright faces, and two sessions with inverted faces, for a total of 4400 trials. We applied reverse-correlation methods coupled with information theory to reveal the image pixels statistically associated with behaviour and neural responses. In both upright and inverted faces, we found that presence of the left eye modulated the reaction times (RTs) of all participants. In upright faces, the eye contralateral to the left and right posterior lateral electrodes strongly modulated early face ERPs. In particular, the N170 latency and amplitude coded the presence of the contralateral eye (Rousselet et al. Journal of Vision 2014, 14(13): 7, 1-24). This association was about 35% weaker in inverted faces, and delayed by about 30 ms, compared to upright face. In conclusion, our results suggest that, in a face detection task, the N170 mostly code the presence of a single feature: the contralateral eye. Inversion leads to an inefficient coding of the same feature, which is reflected in weaker and delayed feature sensitivity. Meeting abstract presented at VSS 2015.