Hi Gang,

I agree that the breadth of activation we observe for a specific cluster reflects the statistical choices that we make for detecting clusters. The absolute breadth of a cluster, however, is not the issue of interest. The critical issue is the relative breadth of two clusters, which I assume is likely to remain at least quite similar across varying statistical thresholds. I assume that the same issue applies to obtaining clusters via differences between two conditions in contrast intensity, with thresholding choices determining the size and average intensity of the clusters obtained.

Perhaps one direction we’ll explore next is to establish confidence intervals for a cluster’s breadth using bootstrapping methods. If we did this for the control condition, we could then see what the probability is of observing a cluster having this breadth in the experimental condition. A similar approach would be to apply permutation methods to the control and experimental conditions, thereby establishing the probability of the difference in cluster breadth observed between them. If we explore these approaches, we’ll vary the statistical thresholds to see how robust the findings are across them.

Thanks again for all your helpful comments and suggestions. If we have any further questions, we’ll let you know.

Best regards, Larry