Perceptual moments of conscious visual experience inferred from oscillatory brain activity

doi:10.1073/pnas.0508972103

Perceptual moments of conscious visual experience inferred from oscillatory brain activity

*Department of Psychology and
^†Centre for Cognitive Neuroimaging, University of Glasgow, 58 Hillhead Street, Glasgow G12 8QB, United Kingdom; and
^‡Départment de Psychologie, Université de Montréal, CP 6128, Succursale Centre-ville, Montréal, QC, Canada H3C 3J7

Edited by James L. McClelland, Carnegie Mellon University, Pittsburgh, PA, and approved February 7, 2006 (received for review November 30, 2005)

Abstract

Transient periods of synchronized oscillating neuronal discharges in the brain have been proposed to support the discrete perceptual moments underlying conscious visual experience. However, the information content of these perceptual moments remains a critical challenge to the understanding of consciousness. We uncovered this information content in four observers who consciously perceived each interpretation of the ambiguous Dali painting Slave Market with the Disappearing Bust of Voltaire. For each individual observer, we isolated the stimulus spatial frequency (SF) features underlying their overt judgments of the input as “the nuns” and “Voltaire”. Every 2 ms between stimulus onset and overt response, we derived the sensitivity of the observer's oscillatory brain activity (in the theta, alpha, and beta bandwidths) to these SF features. Then, in each bandwidth, we estimated the moments (between stimulus onset and perceptual judgment) when perception-specific SF features were maximally integrated, corresponding to perceptual moments. We show that the centroparietal beta oscillations support perceptual moments underlying the conscious perception of the nuns, whereas theta oscillations support the perception of Voltaire. For both perceptions, we reveal the specific information content of these perceptual moments.

Footnotes

^§To whom correspondence should be addressed. E-mail: philippe{at}psy.gla.ac.uk
Author contributions: M.L.S., F.G., and P.G.S. designed research; M.L.S. and P.G.S. performed research; M.L.S., F.G., and P.G.S. analyzed data; and M.L.S., F.G., and P.G.S. wrote the paper.
↵ ¶ We chose to measure from the centroparietal electrode Pz because previous work revealed evidence of nonlinear integration of featural information over this electrode site (30). In contrast, we did not find evidence of such early feature integration on occipitotemporal electrodes (e.g. P9 and P10).
↵ ‖ We band-pass filtered the EEG with a smooth sixth-order Butterworth filter with cutoffs on 4 and 8 Hz for the theta band, 8 and 12 Hz for the alpha band, and 12 and 24 Hz for the beta band.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations:

Abbreviations:

SF,

spatial frequency;

HSF,

high-SF;

LSF,

low-SF;

EEG,

electroencephalogram