[pymvpa] Update on: Suspicious results

[Yaroslav Halchenko]

On Tue, 01 Mar 2011, Nynke van der Laan wrote:
> The design of the fMRI task is as follows: The task exists of 38
> trials = 38 chunks
> One trial consists of the following sequence of events:
> - 4 sec category 1
> - 2 sec fixationcross
> - 4 sec category 2

so both trials are separated only by 2 sec of fixation

> So, in each trial/chunk both category events are presented once. The
> order of category 1/2 in the trial is randomized. So in some trials
> first 1, then 2 or viceversa. Onsets of events category 1 and 2 are
> thus 6 seconds apart, but order is randomized so I would not expect
> problems. Between chunks is also enough time I would expect...

still -- what does SequenceStats report?  and since categories groupped
into trials, it would matter to include also a label for a beginning or
the end of the trial or just fixation or "other event" so it is clear
either there is any order effect.

Also, although you have mentioned "no zscorring" and randomization
showed again right-bias (which is the most intriguing effect for me):
just to make sure -- you have not done any kind "per sample
normalization", e.g. subtracting the sample mean from each sample etc ?

The simplest way to troubleshoot what is going on would be -- why don't
you just share a sample dataset -- I doubt anyone would manage to still
scientific finding but we could be able to actually look at the data.

In PyMVPA 0.4, although somewhat inefficiently, you could do that with
pickling:

Hamster(dataset=dataset).dump('/tmp/example_data.dat.gz')

and then share that example_data.dat.gz -- hopefully we would be able to
load it ;)

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