Figure 5. Effects of spatially reducing the vigilance template.

(A) The template was successively reduced to retain the indicated fraction of highest-magnitude voxels drawn from the set of negative, positive, or both negative- and positive-signed voxels. These reduced voxel sets were used as templates for calculating the fMRI alertness index in each scan. The x-axis indicates the fraction of voxels relative to the whole-brain template; that is, at x = 0.2, we used the highest 20% of positive values (red) and the highest 20% of negative voxels (blue), then combined them to make a joint positive and negative template (magenta). To focus on relative effects, all three lines were normalized to their value at the fraction of 1.0. (B) Template map produced by retaining only the top 1% of positive and negative voxels of the original whole-brain template, respectively. (C) The pre-stimulus fMRI alertness index, generated from this reduced (‘1%”) template, for fast, slow, and missed trials (see Figure 4B for analogous results using the whole-brain template).