Figure 3.

Adapted from Snyder and Foxe (2010). (A) Task schematic. Participants were presented with a word cue (e.g., COLOR or MOTION) at the start of each trial that indicated the relevant feature of the upcoming S2. Following a 1.7 to 2.3-s cue-target interval, a random dot stimulus (S2) was presented for 200 ms. Dots comprising the S2 were all colored and moving. For color targets, two different colors of dots were present in the stimulus (on standard trials, all dots were uniformly colored). For motion trials, some dots moved in a different direction from the rest (on standard trials, all dots moved in the same direction). Participants were instructed to respond with a button press if they detected a target in the cued feature, and to withhold response otherwise. (B) Examples of “feature-sensitive, alpha-reactive” components for two representative subjects. Scalp-recorded data were first separated into independent components using ICA. TSE waveforms were derived for each component by Hilbert-transforming band-pass filtered (8–15 Hz) single-trials and averaging the instantaneous amplitudes across trials. For each participant, a few components were highly dynamic in the alpha range during the preparatory period (“alpha-reactive” components), and some of these alpha-reactive components moreover showed power differences based on which feature was cued (“feature-sensitive”). TSE waveforms illustrating this effect are depicted in violet for two representative subjects. The solid lines represent attention to motion and the dashed/dotted lines represent attention to color. Below the TSE waveforms, running p-values for the alpha power difference between the two attention conditions is plotted in orange. To the right of the TSE waveforms, point-equivalent dipole source estimates for the corresponding components are depicted in a standard MNI brain volume. (C) Localization of all feature-sensitive alpha-reactive components across participants. Components are color-coded according to the direction of feature-sensitivity: components with greater alpha power for attention to color than for attention to motion are plotted in red, and components with greater alpha power for attention to motion than for attention to color are plotted in blue. The distributions of the estimated sources for two types of components are significantly different. Components with higher alpha power for attention to color are generally localized to putative dorsal visual stream regions, whereas components with higher alpha power for attention to motion are generally localized to putative ventral visual stream regions. This pattern of results is consistent with a suppressive role of anticipatory alpha-band power increases.