Invisible flashes bias spatial coding in the auditory system

Abstract

Information integration is widely considered fundamental for human consciousness. Combining spatial ventriloquism and dynamic continuous flash suppression, this psychophysics-EEG study investigated how invisible flashes influence spatial perception of sounds. We show that invisible flashes, even when mislocalized by observers, bias observers perceived sound location. EEG multivariate pattern analyses unravelled that the locations of invisible flashes are encoded in early (150-250ms) neural activity. Crucially, even though this visuospatial information rapidly dissipates for invisible mislocalized flashes, being no longer decodable from neural activity after 300ms, it progressively biases neural encoding of sound location (300-600ms), thereby ultimately inducing a perceptual ventriloquist illusion. Our results demonstrate that subjective awareness is not a prerequisite for integrating information across the senses. Spatial information that dissipates from the visual system and evades awareness biases neural encoding and perception of sound location. These results pose challenges for leading theories of consciousness as a unified all-or-none phenomenon.