Hi
at p=0.5 (alternative) you'll see more activation. If you select
'Output full stats folder' in the GUI you'll get the probability maps
written out to a /stats subdirectory insde the melodic folder... you
can load this into fslview to see what p-level your clusters did
achieve...
hth
christian
On 15 Jan 2008, at 12:53, Angel Wong wrote:
> Dear FSL users
>
> Did anyone encounter the situation of generation of two thresholded IC
> maps for the same component? Could anyone give me more information
> related
> to the interpretation of second thresholded IC map under the null
> hypothesis? If I lower the threshold level to p=0.5 (as default mode),
> would it be a better practice than setting the threshold level to
> p=0.95
> for showing more activation areas in the first thresholded IC map
> under
> the alternative hypothesis?
>
> Your advice on the above questions would be much appreciated.
>
> Many thanks
> Angel
>
> On Sat, 5 Jan 2008 17:25:15 +0000, Angel Wong <[log in to unmask]>
> wrote:
>
>> Hi Christian
>>
>> Thanks for your information. I can see the activation in the first
>> thresholded IC map under the alternative hypothesis is weak (seems no
>> activation), however it can show reasonable activation pattern in the
>> second thresholded IC map under the null hypothesis. But when I
>> interpret
>> these thresholded IC maps, for instance, looking at the second
> thresholded
>> IC map, is there any cautions for the interpretation (is it the same
>> interpretation with the first thresholded IC map)? The weak
>> activation
>> shown in the first thresholded IC map, is it resulted by setting the
>> threshold level (p = 0.95) too high?
>>
>> Cheers
>> Angel
>>
>> On Fri, 4 Jan 2008 20:50:27 +0000, Christian F. Beckmann
>> <[log in to unmask]> wrote:
>>
>>> Hi,
>>>
>>> this happens in cases where the mixture-model based inference step
>>> detects that there is only a single Gaussian distribution present
>>> (i.e. the histogram of the IC does not have fat tails). In this case
>>> both thresholding under the alternative hyp and under the null hyp
>>> becomes valid and melodic generates the latter at a p<0.05 level in
>>> addition to the normal alternative hyp test. There are different
>>> possible ways why this might happen, e.g. SNR is very low or the
>>> mixture model simply failed to find a good estimate - you can check
>>> what's going on by having a look at the mixture-model fit (click on
>>> the thresholded map and you'll see the mm report page)
>>> hth
>>> Christian
>>>
>>>
>>>
>>>
>>>
>>> On 4 Jan 2008, at 15:00, Angel Wong wrote:
>>>
>>>> Dear FSL users I have performed a model-free group analysis using
>>>> multi-subject tensor ICA. The components can be generated properly.
>>>> But when I looked at the results, I found some components contain 2
>>>> thresholded IC maps. One is entitled as 'thresholded IC map
>>>> alternative hypothesis test at p>0.95', another is entitled as
>>>> 'thresholded IC map (2) 2-sided null hypothesis test at 0.05'. I
>>>> would like to ask: 1) Why there are two thresholded IC maps
>>>> generated for some of the components? 2) What is the difference
>>>> between the two thresholded IC maps and their significance? Many
>>>> thanks Angel
>>> =
>>> =
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