First, I was struck again by the strength and consistency of the activations and deactivations associated with the n-back task; they seem as reliable as those from some motor and somatosensory tasks. The authors used a mass-univariate analysis to identify a set of ROIs to use for the MVPA, shown in this part of Figure 2 (warm colors for regions that increased with n-back level, and cool colors for regions that decreased). As the authors properly point out, doing MVPA on the task blocks with these ROIs would be somewhat circular (since a mass-univariate analysis of the task blocks was used to create the ROIs), but their main MVPA avoids circularity, since it was done on a different part of the task.
Next, I appreciated the discussions of possible confounds in the results section: the authors report pairwise accuracies, not just the three-way, explaining that they want to make sure one very accurate pair is not driving the results, and they performed a nice control analysis using randomly-selected rest volumes.
Finally, they found a correlation between classification accuracy (MVPA during task preparation periods) and behavioral performance (participant speed on the n-back task); there are still relatively few reports tying fMRI analyses to behavior, and it's nice to see another one.
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