Prestimulus power and phase of α and β predict visual awareness under high and low expectation

The experimental material was sinusoidal Gabor patch, with a Michelson contrast of 0.03, tilted either 45° to the left or right vertically. The blank stimulus was the no-target. The experimental materials were made from the online-gabor-patch-generator. The background brightness of all these types of stimuli was 22 cd/m². The probability of stimulus presentation was manipulated to present high or low expectations, with a high expectation of 75% stimulus appearance and a low expectation of 25% stimulus appearance. The proportion of stimulus appearance in each block was informed to the participants before the experiment. The experiment was conducted in a quiet, dimly lit EEG laboratory. The experimental stimuli were presented using E-Prime 2.0 software on a screen with a resolution of 1024x768 pixels and a refresh rate of 60 Hz (1 refresh cycle was approximately 17 ms). The participants were approximately 80cm away from the screen. EEG data were recorded using Curry7 software produced by NeuroScan, and the participants wore a 64-electrode cap based on the international 10-20 system. The frontal central electrode was grounded (located at the midpoint of the FCZ and FX line) and the top electrode was the reference electrode. The sampling rate was 1000 Hz in DC mode. Electrodes were placed on either side of the eyes to record horizontal eye movement (HEOG), and electrodes were placed above and below the left eye to record vertical eye movement (VEOG), with a resistance of less than 10 kΩ.