Hi Matt,
Thanks for helping me understand this. Resolution is 3x3x4 mm, TR is 1.5 seconds, and 920 time points. No concatenation. When I did ICA on a different, shorter, dataset (3x3x3mm, TR 2s, 196 timepoints), I similarly got a 150-300 components with smoothed data and much less with unsmoothed data.
Cheers, Kajsa
On Fri, 9 May 2014 10:56:18 -0500, Matt Glasser <[log in to unmask]> wrote:
>What is your resolution, TR, and number of time points per run? Did you
>use one long run or concatenate across runs?
>
>Smoothing would only decrease gaussian noise, which ICA is trying not to
>put into components to begin with.
>
>Peace,
>
>Matt.
>
>>Thanks Christian!
>>
>>Ok, that makes sense. Somehow I had imagined smoothing would have the
>>opposite effect by decreasing noise sources...
>>
>>On to my next worry: From what I've seen people generally get many fewer
>>components, also with spatially smoothed data. My dataset is pretty
>>standard, although the stimuli are very complex (movies). Does anyone
>>have any ideas about why I get so many more components than other people?
>>I'm worried I've made some mistake. Or doesn't this happen sometimes and
>>it's just that I haven't heard of it in the literature? I'm pretty new to
>>this method.
>>
>>Many thanks!
>>Kajsa
|