Figure 1.

Experimental design A, The task was to rate the visibility of target stimuli embedded on a field of random noise. After a fixation cross of variable length was presented, the target stimuli appeared for 500 ms, followed by a question mark indicating subject to give their visibility ratings. To assess visibility, we used the Perceptual Awareness Scale (Overgaard et al., 2006). B, Bottom-up information was manipulated by degrading the stimulus visibility. Six degradation levels were used. Degradation was achieved by decreasing the dot density of the target stimuli while keeping dot density of the background constant. The successive increases and decreases in stimulus degradation are referred to as “sequence.” For the main experiment, the same stimulus was used during a given sequence, whereas in the control EEG experiment, the stimulus was varied every trial.