I see, that makes sense. Thanks, this is very helpful.
Dasa
Steve Smith wrote:
> Hi, the most likely difference is in the estimation of the data
> spatial smoothness.
>
> When you run FEAT, it has access to the GLM residuals (res4d), which
> is the most accurate thing to estimate the spatial smoothness from.
> When you run easythresh, it doesn't have access to this (it could if
> you knew where your residuals are and amended the script), so it
> estimates the smoothness from the unthresholded input statistic image;
> this is slightly less accurate than the former approach and will give
> slightly different smoothness estimation, resulting in slightly
> different p-values.
>
> Cheers, Steve.
>
>
> On 26 Jan 2008, at 01:32, Dasa Zeithamova wrote:
>
>> Hi,
>>
>> I have noticed that cluster p-values provided by easythresh command
>> and those that come from feat GUI when using cluster threshold in
>> post-stats are different. This happens both when using BET-extracted
>> whole brain ("mask.nii.gz") and when using a small volume mask (such
>> as occipital cortex mask). The cluster locations and sizes are
>> identical, but the associated p-values differ (are smaller, "more
>> significant" from feat GUI). I was wondering what algorithms are used
>> to estimate the cluster-associated p-values and what may account for
>> this discrepancy.
>>
>> Thank you,
>> Dasa
>>
>
>
> ---------------------------------------------------------------------------
>
> 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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>
>
