Neural responses during natural vision are action-timed rather than locked to the onset of stable foveal input

Visual processing is traditionally studied using static viewing paradigms in which researchers analyse brain responses to the onsets of a sequence of randomly selected stimuli. Translating this "stimulus onset" approach to active vision paradigms that allow for free eye-movements, researchers often consider fixation onsets as the events that trigger visual activity across the visual system. Here, we test this assumption by analysing a large-scale magnetoencephalography (MEG) dataset with simultaneously recorded eye movements of 5 participants who freely explored thousands of natural images, yielding approximately 200,000 gaze events. We show that saccade-related events, particularly peak saccade curvature, rather than fixation onsets, explain most variance in latency of the early sensory component M100. Further, comparing the classic M100 elicited by stimulus onsets with the M100s elicited during active vision revealed stark differences, both in response to saccade-related and fixation-onset events. This indicates that phenomena discovered using gold standard stimulus onset paradigms do not necessarily translate to natural vision. Our findings challenge the prevailing approach to studying vision in static paradigms and highlight the importance of internally generated and action-driven signals in the dynamics of natural sensory processing.