Abstract
A fundamental problem in vision is to understand which visual information correlates with the perception of a stimulus and how the brain extracts and aggregates this information to arrive at a conscious perception. We examined this problem in a case study involving the perceptual reversal of an ambiguous image (here, Dali's painting the Slave Market with the Disappearing Bust of Voltaire). We applied Bubbles in 3D space (2D image space × 5 spatial scales) to five observers disambiguated the image. We determined the visual information correlated with each perception from the observers' responses (“nuns” vs. “Voltaire” vs. “don't know”). Simultaneously, we recorded the observers' EEG at 1024 Hz with a 64 electro-cap and determined the visual information correlated with modulations of amplitude in the theta, alpha, beta and gamma bandwidths of oscillatory EEG activity.
Brain correlates of conscious perceptions are likely to integrate the scale information that determines the “the nuns” vs. “Voltaire” behavioral responses. To find the time points of highest scale integration, we first derived the sensitivity of oscillatory brain activity to the scale information associated with behavioral responses, independently for each EEG band. We computed these sensitivity curves from −200 to +800 ms around stimulus onset, in 2 ms independent time steps. The sensitivity curves (one for each spatial scale considered) effectively project EEG activity into the space of the scale information associated with perception. To find the time points of highest information integration, we computed phase-locking factors between all possible pairs of sensitivity curves and averaged them.
With this new approach, we were able to isolate the time points at which brain signals are mostly correlated with an integration of the spatial scale information underlying the perception of each observer. This suggests a new approach to find the brain correlates of conscious subjective perceptions.