Hi
> First, what is your usual criteria when looking for task-related components? According to my understanding (please correct me if I am wrong), if the p value of the F-test on full model fit shows significant (e.g. p < 0.00000), this may reflect that the timecourse of that component follows the pattern of the given paradigm, but may have some phase shift from the original paradigm pattern.
Not sure where you're getting the 'phase shift' idea from. If the F test is significant then it mean that your design matrix overall fits into the time course and explains significant amount of variance. At this stage you don;t know which one (or set) of the regressors drive the overall fit - it could be that it's e.g. some confound head motion regressor and not the regressors describing the different experimental conditions...
> So if the p value of the contrast together shows significant (e.g. p < 0.00000), this means that the timecourse is in-phase with the paradigm, and can be considered as task-related response without phase shift. But if the p value of the contrast shows not significant (e.g. p < 1.00000), this may represent that the timecourse is totally out of phase with the paradigm. So what I interpret is that the p value of the F-test helps to determine whether the timecourse follows the given paradigm pattern, and the p value of the contrast helps to determine the degree of phase shift. Am I right?
>
Nope - most basic interpretation is this:
- F determines if the component overall seems to be related to the experiment (is task-related)
- t-contrast ask a specific question (conditionA > condition B maybe)
> Second, what is the meaning of color spectrum shown in thresholded IC maps? Is the red spectrum corresponding to positive response to the decomposed timecourse of that component and the blue spectrum for the negative response?
Yes, though there is room for ambiguity, eg by flipping the spatial map and the time course you'd achieve the same overall decomposition.
>
> Third, how can I observe/interpret the group/task differences in spatial pattern of thresholded IC map if I add contrast matrix for the sessions/subjects mode? If the p value of a contrast (e.g. Group A > Group B) shows significant, does the spatial pattern of thresholded IC map represent the contrast differences between the two groups?
Yes, if a comparison is significant then it means that under the model the entire spatial maps differs in strength in group A relative to B
> If I add more contrasts for comparison, will it affect the number of IC decomposition from the input datasets?
>
No - all the GLM fitting is done post-hoc (after the ICA decomposition has finishes)
hth
Christian
> Thank you for your attention and help in advance.
>
> Best regards,
> Angel
>
> On Sun, Jan 23, 2011 at 4:55 AM, Angel Wong <[log in to unmask]> wrote:
> Hi Prof. Smith,
>
> Thanks for your reply. I have some follow-up questions for clarifying the statistical output. I know if I specify design matrix and contrast matrix for timecourse and subject mode, the Melodic will generate two GLM regression fit tables for the timecourse and subject mode respectively. But if I want to look for task-related components, should I look at the p values in the contrasts column? What does it represent if it is significant for the F-test on full model fit, but not significant for the contrasts and vice versa? As far as I know, if the p value of a contrast shows that it is significant should represent the timecourse of that component is significantly active/valid corresponding to that contrast. So if it shows that the p value of a contrast is significant, then the p value for the F-test on full model fit should also be significant, but it is not always true for the opposite direction. Am I right?
>
> For the sessions/subjects mode, if I define '1' as group1 and '2' as group2, C1 represents group1 > group2 and C2 represents group2 > group1. If p value for C1 is significant, can I say that the 'activated' regions (indicated by red color) shown in that component is significantly larger in group1 compared with group2, or 'deactivated' regions (indicated by blue color) is significantly smaller in group1 than group2?
>
> Maybe I am a bit confused with the basic concept of the TICA, and may not deliver my questions clearly. But I am glad if you can give me a clearer concept for the interpretation of the results (between spatial pattern, temporal pattern and subjects mode).
>
> Best regards,
> Angel
>
>
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