Perceptual filling-in (PFI) happens when a visible target disappears from conscious awareness and its location is filled in by the surrounding background. This study tracked brain activity using steady-state visually evoked potentials (SSVEPs) while participants reported when four peripheral targets disappeared or reappeared against a dynamically updating background. Background SSVEPs closely matched subjective reports and increased with more filled-in targets. Unexpectedly, as more targets filled in, the duration of disappearances grew, suggesting facilitatory interactions across visual quadrants. Distinct spatiotemporal correlates appeared: before genuine PFI, the second harmonic (40 Hz) increased before the first (20 Hz), possibly linked to attention, a pattern absent for physically removed stimuli. These findings show PFI can study multi-object perceptual suppression and reveal distinct neural correlates for endogenous versus exogenous changes in consciousness.
Perceptual filling-in (PFI) makes a visible target disappear from awareness while the background fills its location. In this experiment, participants viewed four peripheral targets on a background updating at 20 Hz. Brain activity tracked via steady-state visually evoked potentials (SSVEPs) showed that background signals closely matched participants' reports of target disappearances. More filled-in targets led to longer disappearances, suggesting interactions between targets in different visual quadrants. Distinct neural responses appeared at different harmonics: the second harmonic (40 Hz) increased before the first (20 Hz) prior to genuine PFI, possibly reflecting attention. No such difference occurred for physically removed stimuli. The results demonstrate PFI as a tool for studying multi-object perceptual suppression and the neural correlates of consciousness.