Investigating Saccade-Onset Locked EEG Signatures of Face Perception during Free-Viewing in a Naturalistic Virtual Environment.

Current research strives to investigate cognitive processes under natural conditions. Virtual reality and EEG are promising techniques combining naturalistic settings with close experimental control. However, many questions and technical challenges remain, e.g., are saccade onsets a suitable replacement of fixation onsets as key events in continuous gaze trajectories ( Amme et al., 2024), and consequently, can VR capture differences across different stimulus categories associated with varying saccade durations? To address both questions, we investigate the N170 face effect in humans (14 males, 19 females, zero diverse) using a free-viewing and free-movement immersive VR study that contained houses, various background stimuli, and, notably, static and moving pedestrians to study face perception under naturalistic conditions. Our results show that aligning trials to saccade onsets leads to more well-defined ERPs than fixation onsets, especially for the P100 component, demonstrating that saccade-onset ERPs are a better-suited analysis method for this type of experiment. Furthermore, we observe an evolution of category-based differences, i.e., face versus background saccade-onset ERPs, compatible with previous reports but extending in a large temporal window and including all electrode sites at different points in time. In summary, employing VR, EEG, and eye-tracking to investigate differences across fixation categories provides insights into the relevance of saccadic onsets as event triggers and enhances our understanding of cognitive processes in naturalistic settings.