PMC

Grand averaged spectral amplitude for electrode PO8 (top) and grand averaged ERPs for electrode PZ (bottom left) for each stimulus category in experiment 3. P3 (390–590ms) and gamma (360–440ms; 30–40Hz) difference amplitudes (shape minus random) are plotted for the same electrodes (bottom right; colors same as in ERPs).

Example stimuli from experiment 3. The shapes were always task-relevant while the target stimulus was manipulated across blocks of trials. Each of the four shapes served as a target in some conditions and the non-target stimuli were categorized according to target-similarity. Note that the actual stimuli consisted of 20×20 grids of line segments and were arranged less densely than shown here. A video example can be viewed online: http://youtu.be/lTZgY42s1YE.

Grand averaged ERPs and difference topographies (shape minus random) during conditions in which the shapes were irrelevant (top) or relevant (bottom) to the task. Grand averaged spectral amplitude for electrode PO8 along with difference topographies are plotted to the right of the ERP data for each condition. ERPs and gamma band activity elicited by the color stimuli are provided in .

Example stimulus sequence from experiment 2. Task relevance of the shape and color patch stimuli was manipulated across blocks of trials. Subjects attended to either the color stimuli or the shape stimuli to detect designated targets (3 or 4 patches of color; vertical or horizontal rectangles). As in experiment 1, actual stimuli consisted of 20×20 grids of lines and are displayed here as 10×10 grids for demonstration purposes. A video example can be viewed online: http://youtu.be/RpcEWi7iB_4.

(Left) Grand averaged ERPs at a representative electrode site (CZ) and difference wave scalp topographies (square minus random; posterior view of scalp) during each phase of the experiment. (Right) Grand averaged time-frequency plot of spectral amplitude at electrode PO7 along with difference topographies for the same three phases of the experiment. Note that only data from the group of subjects (N=16) who were inattentionally blind to the square patterns during phase 1 of the experiment are shown here. Similar data for the group of subjects (N=16) who spontaneously noticed the square patterns in phase 1 are provided in .

Grand averaged ERPs (left) and difference wave maps (right) showing the earlier ERP effects (Nd1, Nd2) observed in experiment 1. The ERPs are plotted for a representative electrode (OZ), and the difference maps (square minus random) reflect mean amplitudes across successive time intervals. For more details, see and . Nd1 = first negative difference; Nd2 = second negative difference; SN = selection negativity; LOP = late occipital positivity; P3b = centro-parietal positivity. *Note all maps in phase 3 are scaled from −4 to +4μV except the first map (Nd1) which is scaled −1.2 to +1.2μV. Reproduced from .

Example stimulus sequence from experiment 1. Stimuli were identical across the three phases of the experiment. In phases 1 and 2 subjects attended to the outer red ring of discs to detect occasional dim disc targets. Half of the subjects in phase 1 did not notice (i.e., were inattentionally blind to) the shape patterns formed by the line segments. In phase 3 subjects attended to the line segments to detect occasional diamond shaped targets (not shown). ERPs and spectral analyses were time-locked to changes in line orientations. Note that actual stimuli consisted of 20×20 grids of lines and are displayed here as 10×10 grids for demonstration purposes. A video example can be viewed online: http://youtu.be/8-9NAFUn_CI.