2° eccentricity. The orientation of the background bars was randomly chosen from 0° to 180°. There were five possible orientation contrasts between the foreground bars and the background bars: 0°, 7.5°, 15°, 30°, and 90°. The mask stimulus (Figure 1B) had the same grid as the texture stimuli. Each mask element contained 12 intersecting high-luminance bars (120 cd/m2) oriented from 0° to 165° at every 15° interval. The bars in the mask had the same size and shape as those in the texture stimuli. Visual stimuli were displayed on an IIYAMA color graphic monitor (model: HM204DT; refresh rate: 60 Hz; resolution: 1024 × 768; size: 22 inches) at a viewing distance of 57 cm. Subjects’

head position was stabilized using a chin rest. A mTOR inhibitor white fixation cross was always present at the center of the monitor. Each trial began with the fixation. A texture stimulus was presented for 50 ms, followed by a 100 ms mask and another 50 ms fixation interval. The foreground region in the

texture stimulus could serve as a cue to attract spatial attention. Then a two-dot probe was presented for 50 ms at randomly either the foreground region (valid cue condition) or its contralateral Selleck Torin 1 counterpart (invalid cue condition) (Figure 1C) with equal probability. Subjects were asked to press one of two buttons to indicate whether the upper dot was to the left or right of the lower dot. The experiment consisted of ten blocks. Each block had 96 trials, from randomly interleaving 24 trials from each of the four orientation contrasts (7.5°, 15°, 30°, and 90°) between the

foreground and background bars. The attentional effect for each orientation contrast was quantified as the difference between the accuracy of the probe task performance in the valid cue and the invalid cue conditions. All subjects also underwent a two-alternative forced choice (2AFC) experiment to determine whether crotamiton the masked foreground region was indeed invisible in a criterion-free way. The stimuli and procedure in this 2AFC experiment were the same as those in the attention experiment, except that no probe was presented. After the presentation of a masked texture stimulus, subjects were asked to make a forced choice response regarding which side (lower left or lower right) from the fixation they thought the foreground region appeared. They performed at chance level in this 2AFC experiment for all four orientation contrasts, providing an objective confirmation that the masked foreground region was indeed invisible. The experimental setup and procedure were similar to those in the 2AFC experiment. There were four possible orientation contrasts (0°, 7.5°, 15°, and 90°) in the texture stimuli. The experiment consisted of 20 blocks of 80 trials, 400 trials for each orientation contrast. Scalp EEG was recorded from 64 Ag/AgCl electrodes positioned according to the extended international 10–20 EEG system. Vertical electro-oculogram (VEOG) was recorded from electrodes placed above and below the right eye.