A multiple-response frequency-tagging paradigm measures graded changes in consciousness during perceptual filling-in.

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.

Study at a glance

Abstract

Perceptual filling-in (PFI) occurs when a physically present visual target disappears from conscious perception, with its location filled-in by the surrounding visual background. These perceptual changes are complete, near instantaneous, and can occur for multiple separate locations simultaneously. Here, we show that contrasting neural activity during the presence or absence of multi-target PFI can complement other findings from multistable phenomena to reveal the neural correlates of consciousness (NCC). We presented four peripheral targets over a background dynamically updating at 20 Hz. While participants reported on target disappearances/reappearances via button press/release, we tracked neural activity entrained by the background during PFI using steady-state visually evoked potentials (SSVEPs) recorded in the electroencephalogram. We found background SSVEPs closely correlated with subjective report, and increased with an increasing amount of PFI. Unexpectedly, we found that as the number of filled-in targets increased, the duration of target disappearances also increased, suggesting that facilitatory interactions exist between targets in separate visual quadrants. We also found distinct spatiotemporal correlates for the background SSVEP harmonics. Prior to genuine PFI, the response at the second harmonic (40 Hz) increased before the first (20 Hz), which we tentatively link to an attentional effect, while no such difference between harmonics was observed for physically removed stimuli. These results demonstrate that PFI can be used to study multi-object perceptual suppression when frequency-tagging the background of a visual display, and because there are distinct neural correlates for endogenously and exogenously induced changes in consciousness, that it is ideally suited to study the NCC.