Who wins the race for consciousness? Ask the phase of ongoing ~7Hz oscillations.
35.18, Sunday, 17-May, 5:15 pm - 7:15 pm, Talk Room 1
Marina Inyutina1,2, Hsin-Mei Sun3, Chien-Te Wu3, Rufin VanRullen1,2; 1Université de Toulouse, CerCo, Université Paul Sabatier, Toulouse, France, 2CNRS, UMR 5549, Faculté de Médecine de Purpan, Toulouse, France, 3School of Occupational Therapy, College of Medicine, National Taiwan University
Most visual stimuli enter perceptual consciousness when they enter the visual field. However, in some cases, such as during Motion-Induced Blindness (MIB), a stimulus spontaneously disappears and re-enters consciousness without any external cause. We have previously shown that the latter type of conscious access is faster by ~100ms than the former, even after sensory latencies are accounted for (Wu et al., Current Biology, 2009). This leads to a surprising temporal reversal in which a sudden transient, such as a color change in a MIB-suppressed target, can cause the target to return to consciousness, yet will often be perceived to occur later: the target reappears with its old color and then changes to the new one. In the race for consciousness, old unconscious information leads against new information. Where does this lead come from, and what factors affect it? We hypothesized that brain oscillations, which have been suggested to play a role in establishing, maintaining and suppressing conscious representations, could affect the magnitude of the lead. To assess this, we recorded EEG while observers (N=16) viewed an MIB display. At a fixed delay after the reported perceptual disappearance of the green target, we abruptly changed its color to purple, resulting in the near-instantaneous return of the target to consciousness. After each trial, observers reported the target color at the time of reappearance. As found previously, an illusory reversal (old-color first) happened on a significant proportion of trials (45%). Crucially, the phase of ongoing 6-7Hz EEG oscillations significantly affected this proportion: at some phases the old information was more likely to win, while the new information was favored at the opposite phase. Over centro-parietal electrodes, where this effect was maximal, the modulation strength reached 14.5%. We conclude that the race for consciousness is decided on a rhythmic basis, with ~150ms-long cycles.