Hi - no I'm afraid that doesn't make sense - Featquery is most
commonly used to summarise/investigate the results of the univariate
GLM analysis that was actually run, not to give you stats on what you
would have gotten if you had prespecified an ROI and averaged the
timeseries data over that ROI. Hence Featquery's application of a
mask to the various images output by the FEAT timeseries stats is
what people generally need.
Cheers, Steve.
On 27 Jul 2007, at 12:17, Daniel Irlam wrote:
> Hello
>
> I have a theoretical question about the logic of the Featquery ROI
> analysis.
>
> As I understand it, the way Featquery currently runs, when used
> with a mask, is the following:
>
> (1) Take the output stats from the univariate 1st level FEAT GLM
> analysis
> (2) For each voxel in the mask extract the desired user statistic
> (e.g. COPE, % signal change, z-score etc)
> (3) Apply some user specifed measure for aggregation of the spatial
> statistics (e.g. mean, median, max, 90th %tile
> of the above)
>
> Would it not make more sense to do:
>
> (1) Apply the ROI mask to the 4d timeseries of the voxels in the ROI
> (2) Apply user specified measure for aggregation across space to
> generate a single timeseries
> (3) Run FEAT on this single timeseries to produce desired user
> statistic (e.g. COPE, % signal change, z-score etc)
>
> One advantage of this reorder would be that the choice of spatial
> aggregation statistics in the new step 2 would seem to be far
> more robust and less arbitrary than in the current way Featquery
> works. It probably only makes sense to use the mean,
> median or first principal component from a PCA (and these
> presumably would be rather similar) for spatial aggregation of the
> timeseries in step 2. Conversely, in the current Featquery a wider
> range of different choices for spatial stats can be argued as
> justifiable by the user (say, mean vs max), and these can produce
> markedly different results.
>
> many thanks
>
> Daniel
>
> --
> Daniel Irlam Ph.D
> [log in to unmask]
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Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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