Measuring graded changes in consciousness through multi-target filling-in
bioRxiv Preprint Server August 7, 2019 Matthew J Davidson, Irene Graafsma, Naotsugu Tsuchiya et al. preprint
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.