Early correlates of visual awareness in the human brain: Time and place from event-related brain potentials

Abstract

When something appears, how soon is the first neural correlate of awareness of it, and where is that activity in the brain? To answer these questions, we measured the electroencephalogram under conditions in which visual stimuli changed identically but in which awareness differed. We manipulated awareness by using binocular rivalry between orthogonal gratings viewed one to each eye. Then we changed the orientation of the grating to one eye to be the same as that to the other eye. Because of the rivalry, sometimes this happened to the visible grating, producing a clear change in perceived orientation, and other times it happened to the invisible grating, producing no change in perceived orientation. This procedure allowed us to analyze time-locked topographic scalp and tomographic primary current densities of the event-related potentials to physically identical events differing in their perceptual consequences. When the change in orientation reached awareness, neural responses began at about 100 ms, spreading mainly from dorsal occipital areas. When the change in orientation did not reach awareness, neural responses also began at about 100 ms, but they were attenuated, particularly in the right fusiform gyrus. We place the earliest correlate of visual awareness following binocular rivalry in the ventrolateral occipitotemporal cortex.

Event-related brain potential correlates of visual awareness

“…Thus, the change in awareness was associated with early negativity, similar to VAN, followed by later positivity (LP). Further studies have revealed the same pattern with the addition that changes have elicited also an early positive enhancement in P1 range (Roeber and Schrö ger, 2004;Roeber et al, 2008;Veser et al, 2008).…”

“…The early awareness-related enhancement of P1 emerges in response to reduced contrast stimuli (Pins and ffytche, 2003;Wilenius and Revonsuo, 2007), change detection (Busch et al, in press;Pourtois et al, 2006) or during perception of bistable stimuli, that is, during binocular rivalry (Roeber and Schrö ger, 2004;Roeber et al, 2008;Veser et al, 2008) or the perception of a Necker lattice Bach, 2005, 2006). Also a MEG study (Boehler et al, 2008) found a difference between effectively vs. ineffectively masked stimuli in the P1 time window around 100 ms.…”

Event-related potential correlates of sound organization: Early sensory and late cognitive effects

“…For example, Valle-Inclan et al (1999) found that stimuli presented to the dominant eye elicited higher ERP responses compared to stimuli presented to the suppressed eye under rivalrous conditions. Their percept-dependent ERP effects started at 70 ms from stimulus onset (see also Roeber et al, 2008;Veser, O'Shea, Schroger, Trujillo-Barreto, & Roeber, 2008).…”

Expectations Change the Signatures and Timing of Electrophysiological Correlates of Perceptual Awareness

“…Previous studies have suggested either early (ϳ100 ms) (Pins and Ffytche, 2003;Roeber et al, 2008) or late (ϳ300 ms) (Sergent et al, 2005;Del Cul et al, 2007) activity correlated with visibility. Our results, however, suggest that the signatures of visibility are not bound to processes with a strict latency but depend on the presence of expectations (Banquet and Grossberg, 1987).…”