Four contrasts (e.g., [UU versus baseline], [DD versus baseline], [DU versus baseline], [UD versus baseline]) were combined and tested against the conjunction null hypothesis where one or more effects are null61,62.
The conjunction results were then tested against the "conjunction null hypothesis", which entailed using the critical t-values for just one contrast, to determine whether there was significant neural activity in certain brain regions in all singing tasks [61].
Conjunctions were calculated based on the minimum t-statistic compared against the conjunction null (Nichols et al. 2005).
The statistical map resulting from the conjunction null was identical to the simple effect of (clear − rot)—that is, the activation generated by (NV − rotNV) encompassed the activation of (clear − rot), but not vice versa (Table 1).
Note that the conjunction null map is not shown in the figure, as it was identical to (clear − rot).
Conjunction of the 2 contrasts of interest (nl > nm) and (nm > ns) was calculated based on the minimum t-statistic compared against the conjunction null (Nichols et al. 2005).
We further investigated activations associated with both stopping and shifting, or with both complex and simple stopping, using second-level random effects conjunction analyses against the conjunction null hypothesis in whole-brain analyses.
Based on the conjunction null hypothesis, a threshold of P < 0.05 FDR corrected and k > 10 voxel was applied to all contrast images used [Nichols et al., 2005].
Conjunction analyses were performed testing the "conjunction null" hypothesis.
The Conjunction Null analysis is stricter than Conjunction Global, which tests "the null hypothesis" that "no subject/contrast activated this pixel" and therefore rejecting the null hypothesis leads to the conclusion that "at least one subject/contrast activated this pixel".
Subsequently a conjunction analysis with a conjunction null hypothesis was carried out to find areas common to the two connectivity group maps, i.e., pre-SMA bilateral).
