Early neural responses to nonconscious fearful and neutral faces - an ERP study

Abstract

Prioritized processing of fearful compared to neutral faces is reflected in differential event-related potentials (ERPs). There is an ongoing debate about the extent to which faces in general and fearful faces in particular enhance specific ERPs if they are not consciously perceived. Specifically, the N170 has been suggested as the most likely candidate for enhanced processing of nonconscious fearful faces. In this pre-registered study, we tested in a large sample based on sequential Bayesian sampling (N = 64) whether early components of the ERP (P1, N170, and early posterior negativity; EPN) discriminate between fearful faces, neutral faces, and non-facial control stimuli. Consciousness was manipulated by presenting stimuli for 17 ms in a backward masking design, with the mask following immediately or after a delay of 200 ms. Participants rated their subjective perception on a perceptual awareness scale in each trial. Importantly, only trials in which nothing but the mask was perceived were considered for the analysis of nonconscious effects. The results showed strong evidence for an increased N170 in response to nonconscious fearful compared to neutral faces; however, this difference was significantly smaller than in the conscious condition. Furthermore, we obtained strong evidence for N170 differences between nonconscious faces and no-faces. For P1 and EPN amplitudes, no significant effects were observed in the nonconscious conditions, although exploratory analyses of the P1 peak interval suggest nonconscious face-no-face differentiation. These results support the notion that nonconscious emotion and face processing are detectable in early neural responses and show that these nonconscious effects are considerably weaker than the corresponding conscious effects.