Effects of low-level visual information and perceptual load on P1 and N170 responses to emotional faces

Emotional facial expressions lead to modulations of early event-related potentials (ERPs). However, it has so far remained unclear in how far these modulations represent face-specific effects rather than differences in low-level visual features, and to which extent they depend on available processing resources. To examine these questions, we conducted two preregistered independent experiments (N = 40 in each experiment) using different variants of a novel task which manipulates peripheral perceptual load across levels but keeps overall visual stimulation constant. Centrally, task-irrelevant angry, neutral and happy faces and their Fourier phase-scrambled versions, which preserved low-level visual features, were presented. The results of both studies showed load-independent P1 and N170 emotion effects. Importantly, we could confirm by using Bayesian analyses that these emotion effects were face-independent for the P1 but not for the N170 component. We conclude that firstly, ERP modulations during the P1 interval strongly depend on low-level visual information, while the emotional N170 modulation requires the processing of figural facial features. Secondly, both P1 and N170 modulations appear to be immune to a large range of variations in perceptual load.