Combining voxel intensity and cluster extent with a permutation test framework

Voxel intensity-based tests provide good sensitivity for high intensity signals, whereas cluster extent-based tests are sensitive to spatially extended signals. To benefit from the strength of both, we consider combining intensity and extent information. We generalize previous work by proposing the use of weighted combining functions. Using a combining framework with permutation tests, we consider a variety of ways of combining voxel intensity and cluster extent information without knowing their distribution. Further, we propose meta-combining, a combining function of combining functions, which integrates strengths of multiple combining functions into one single statistic. Using real data, we demonstrate that combined tests can be more sensitive than voxel or cluster size test alone. Though not necessarily sensitive than individual combining functions, the meta-combining function is sensitive to all types of signals, thus can be uses as a single test summarizing all the combining functions.