[pymvpa] Help needed untangling searchlight accuracy bias

[Mike E. Klein]

Ah! I think I see what it is then… I'm likely feeding something like
-1s and 1s (only!) into the searchlight!

I'll try out your suggestions and reply shortly (just stepped away
from the computer)… thanks again!

On Thu, Oct 20, 2011 at 3:27 PM, Yaroslav Halchenko
<debian at onerussian.com> wrote:
>
>
> On Thu, 20 Oct 2011, Mike E. Klein wrote:
>> Thanks for the quick response. I actually don't know how to crossplot…
>
> should be as easy as
>
>    import pylab as pl # not needed if you did import from mvpa.suite
>    pl.plot(np.ravel(s1_map), np.ravel(s2_map), '.')
>    pl.show() # your might not even need this one
>
> alternatively -- here is a helper I hacked up/use -- probably should
> place it under PyMVPA (see attached) -- just give it two nifti files ;-)
>
>> histrograms are output from MRICron.
>
>    pl.hist
>
> should become your friend
>
>> I've tried to follow the plotting
>> from the searchlight example from the manual, but haven't figured out
>> to get my searchlight data in there (from nifti) without running the
>> entire multi-hour script first.
>
> just load using fmri_dataset with the original mask ;)
>
>> As far as ds.summary, I've pasted below. It has been run averaged, but
>> not detrended or zscored.
>
> if I were you I would have detrended, zscored and only then averaged!
>
> if averaging was done across multiple conditions spread through the
> 'run' detrending might be detremental
>
> and I think I might know where other catch could be -- if you
> zscore such a dataset as you have (2 samples total per chunk) with
> zscoring per chunk -- do you know what values would you get? ;)
>
> so -- how was zscoring done?
>
> what about ds.summary() right before you fed it into searchlight?
>
> --
> =------------------------------------------------------------------=
> Keep in touch                                     www.onerussian.com
> Yaroslav Halchenko                 www.ohloh.net/accounts/yarikoptic
>
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