A multiple-response frequency-tagging paradigm measures graded changes in consciousness during perceptual filling-in.
Neuroscience of consciousness January 1, 2020 Matthew J Davidson, Irene L Graafsma, Naotsugu Tsuchiya et al.
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.