>From your original mail: I agree with Dr. Kanwisher. When you ask if it is >appropriate to "(visually) compare" list of regions, I would answer that it is >absolutely not. A direct comparison is necessary. See e.g. Nieuwenhuis et al., >2011, Nature Neuroscience.
For your second, I would say that it is not correct. Again, you should directly compare them. Otherwise, what are you basing the conclusion on? What effect size difference would you use as a cut-off between a "real" and "not real" difference? I think reading the above-mentioned paper will help with this question as well. ________________________________ From: freesurfer-boun...@nmr.mgh.harvard.edu <freesurfer-boun...@nmr.mgh.harvard.edu> on behalf of Francesco Puccettone <francesco.puccett...@gmail.com> Sent: Thursday, August 27, 2015 1:20 PM To: Freesurfer@nmr.mgh.harvard.edu Subject: Re: [Freesurfer] Comparing lists of activated regions between task>ctrl contrasts Sorry, forgot to add one additional (related) question: is it ever correct to say "for region Y, the activations found for taskA were smaller than for taskB" just based on the two contrasts taskA>baseline and taskB>baseline? Or is it necessary that taskA and taskB be contrasted directly to be able to draw any conclusions (if any are sensible) about what smaller/larger activations of a certain region might mean? Thanks! On 27 August 2015 at 19:13, Francesco Puccettone <francesco.puccett...@gmail.com<mailto:francesco.puccett...@gmail.com>> wrote: Hello all, I have seen several (older) papers that draw conclusions about the implication of a brain region in a given task by using the following logic: region X was activated in the contrast taskA>baseline, but not in the contrast taskB>baseline; therefore, region X is implicated in/essential for the cognitive processes underlying taskA, but not also for that underlying taskB; in other words, it dissociates between the two tasks. I believe Nancy Kanwisher addresses this point in a video lecture where she was pointing out that the above logic is flawed, and that said conclusion can only be drawn if the two tasks are contrasted directly (A>B). Have I understood this correctly, and does it ever make any sense to draw inferrences about implicated brain regions based on (visually) comparing the list of regions produced by contrasts comparing each task to the same baseline (in other words, by noticing which brain regions appear in one list, but not in the other)? Or, on the contrary, do all statistics and corrections need to be done voxel-wise, which is something that is only done when contrasting the two tasks directly? Many thanks for any opinions. --Francesco
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