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Dear Paul: exactly! I would imagine however, that you would attempt to find that behavioral indicator, even if it is post hoc and try to test it in a second experiment. Cheers, nader Paul Fletcher wrote: > Hello, > Just a though on a fascinating discussion. > I agree that, ultimately, one needs to express task-specific functional > neuroimaging differences in terms of some other measure. However, the > absence of a behavioural measure in the presence of a functional imaging > activation does nothing, in itself, to abnegate the validity of the imaging > observation. Rather it feeds back to our behavioural measurements and > encourages us to explore the behavioural outcomes of our tasks more > thoroughly. > Consider the developing literature (itself rooted in ERP work) showing > that, if a subject learns a list of words under apparently identical > behavioural conditions, and then if subsequent behavioural memory retrieval > measures are used to categorise these words according to whether or not > they were subsequently recalled, then we can separate those words that were > successfully encoded from those that were not and identify a regional BOLD > response that characterises this difference. Here we have a behavioural > difference that is only obtained after scanning has occurred and the > challenge is to find a behavioural measure that is measurable during the > scanning and differentiates abetween successfully and unsuccessfully > encoded words as sensitively as does our imaging measure. > It seems to me that behavoiural measures may be no less subject to error > and insensitivity than imaging measures. Just as observing that an imaging > study fails to distinguish between two conditions that are clearly > separable at the behavioural level cast doubt upon our imaging findings, so > is the reverse true. > We must keep the faith and believe our imaging data. > > Very best wishes > Paul Fletcher > > At 08:51 31/05/01 -0400, you wrote: > >Dear Russ: > > > >I am sure I am being naive, but is it not the case that this obviates the > whole > >idea of functional, in fMRI. In the absence of any reliable behavioral > >indicators, as well as a control condition, how can we be sure that any > >activation > >is the results of that particular function. I see many papers in the > field that > >do this > >so I would really appreciate it if someone explained the logic of looking at > >activation > >across conditions when there are no behavioral differences across > conditions. It > >seems > >to me that in the absence of some reliable external behavioral indicator > we have > >circular > >argument for the role of that particular function in activation of a region. > > > >thank you in advance, > > > >Nader > > > >Russ Poldrack wrote: > > > >> I would think that it is quite reasonable to analyze the imaging data > across > >> conditions that don't show any differences in RT or accuracy, > particularly if > >> there are hypotheses about differential activation across the conditions in > >> question. For one, it could be the case that there is some cognitive > process > >> that varies across the conditions but the behavioral measure is not > sensitive > >> enough to find this difference whereas the imaging measure might be more > >> sensitive. > >> > >> cheers, > >> russ > >> > >> Greig de Zubicaray wrote: > >> > >> > Dear all, > >> > > >> > I have a thorny question motivated by a reviewer's comments on one of our > >> > fMRI papers. > >> > > >> > Briefly, we used a memory task with variable delay periods. However, > we did > >> > not find significant differences in terms of either accuracy or RT across > >> > the delays. Therefore, we did not look for an effect of delay in the fMRI > >> > data. The reviewer is requesting that we revise the paper to include this > >> > analysis. > >> > > >> > Does anyone know of any references addressing whether it's "good form" to > >> > perform analyses of neuroimaging data in the absence of a significant > >> > behavioural effect? Any views on this issue? > >> > > >> > Any help would be appreciated. > >> > > >> > Regards, > >> > > >> > Greig > >> > > >> > -- > >> > Dr Greig de Zubicaray > >> > Centre for Magnetic Resonance > >> > The University of Queensland > >> > Brisbane, QLD 4072 > >> > AUSTRALIA > >> > > >> > Tel: +61 (0) 7 3365 4250 [direct] > >> > +61 (0) 7 3365 4100 [CMR] > >> > Fax: +61 (0) 7 3365 3833 > >> > >> -- > >> Russell A. Poldrack, Ph. D. > >> MGH-NMR Center > >> Building 149, 13th St. > >> Charlestown, MA 02129 > >> > >> Phone: 617-726-4060 > >> FAX: 617-726-7422 > >> Email: [log in to unmask] > >> Web Page: http://www.nmr.mgh.harvard.edu/~poldrack > > > ----------------------------------------------------------------- > Paul Fletcher, > Box 189, > Research Department of Psychiatry, > University of Cambridge, > Addenbrooke's Hospital, > Hills Road, > Cambridge, > UK > CB2 2QQ > > Tel 01223 336 988 > Fax 01223 336 581