[pymvpa] Help needed untangling searchlight accuracy bias

[Mike E. Klein]

Hi,

Thanks for the quick response. I actually don't know how to crossplot…
I haven't been able to figure out plotting from python. The
histrograms are output from MRICron. 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.

As far as ds.summary, I've pasted below. It has been run averaged, but
not detrended or zscored.

Thanks again,
Mike

In [27]: print dataset.summary()
Dataset: 54x46174 at float64, <sa:
chunks,targets,time_coords,time_indices>, <fa: thr_glm,voxel_indices>,
<a: imghdr,imgtype,mapper,voxel_dim,voxel_eldim>
stats: mean=8388.38 std=4397.79 var=1.93406e+07 min=63.33 max=25721.7

Counts of targets in each chunk:
  chunks\targets condish1 condish2
                  ---    ---
       0.0         1      1
       1.0         1      1
       2.0         1      1
       3.0         1      1
       4.0         1      1
       5.0         1      1
       6.0         1      1
       7.0         1      1
       8.0         1      1
       9.0         1      1
      10.0         1      1
      11.0         1      1
      12.0         1      1
      13.0         1      1
      14.0         1      1
      15.0         1      1
      16.0         1      1
      17.0         1      1
      18.0         1      1
      19.0         1      1
      20.0         1      1
      21.0         1      1
      22.0         1      1
      23.0         1      1
      24.0         1      1
      25.0         1      1
      26.0         1      1

Summary for targets across chunks
  targets mean std min max #chunks
  condish1     1   0   1   1     27
 condish2    1   0   1   1     27

Summary for chunks across targets
  chunks mean std min max #targets
    0      1   0   1   1      2
    1      1   0   1   1      2
    2      1   0   1   1      2
    3      1   0   1   1      2
    4      1   0   1   1      2
    5      1   0   1   1      2
    6      1   0   1   1      2
    7      1   0   1   1      2
    8      1   0   1   1      2
    9      1   0   1   1      2
   10      1   0   1   1      2
   11      1   0   1   1      2
   12      1   0   1   1      2
   13      1   0   1   1      2
   14      1   0   1   1      2
   15      1   0   1   1      2
   16      1   0   1   1      2
   17      1   0   1   1      2
   18      1   0   1   1      2
   19      1   0   1   1      2
   20      1   0   1   1      2
   21      1   0   1   1      2
   22      1   0   1   1      2
   23      1   0   1   1      2
   24      1   0   1   1      2
   25      1   0   1   1      2
   26      1   0   1   1      2
Sequence statistics for 54 entries from set ['condish1', 'condish2']
Counter-balance table for orders up to 2:
Targets/Order O1     |  O2     |
    major:     0 27  |  26  0  |
   perfect:   26  0  |   0 26  |
Correlations: min=-1 max=1 mean=-0.019 sum(abs)=53


On Thu, Oct 20, 2011 at 2:55 PM, Yaroslav Halchenko
<debian at onerussian.com> wrote:
> just for completeness :
> what is the output of
>
> print ds.summary()
>
> ?
>
> also, if you crossplot A against A* -- how does it look?
>
> On Thu, 20 Oct 2011, Mike E. Klein wrote:
>
>> Hi everyone,
>
>> Thanks in advance for any help and sorry for the length of this:
>
>> I've been performing a searchlight analysis on fMRI data from an
>> auditory experiment I conducted. Running a whole-brain searchlight on
>> binary comparisons is showing a consistent right-bias in accuracies.
>> Typically I can see a smallish peak centered directly on 50% and then
>> a much larger peak in the 65% range. I'm pretty sure something fishy
>> is going on, as I scrambled the order of my runs in the attribute file
> --
> =------------------------------------------------------------------=
> Keep in touch                                     www.onerussian.com
> Yaroslav Halchenko                 www.ohloh.net/accounts/yarikoptic
>
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