[pymvpa] ERNiftiDataset with different event durations

Yaroslav Halchenko debian at onerussian.com
Thu Jul 16 15:11:35 UTC 2009

in your case -- do you have a balance in how many delays of different
length (1,2,3) you use across conditions A and B? if not (ie if you have
preference for 2 delays for A and 3 delays for B), then if you take more
than 1 volume after, classifier might classify purely on the effect of
having longer delays for B, ie you would not catch actual neural
phenomena of difference between A and B, but rather just a fact
that it is more probably to see TGT_ for A sooner.

If you have the balanced (ie the same number of trials with 1, 2, 3
delays for both A and B), then, I think, classifier would actually try to
classify on the differences among conditions A and B, since it would not
be able to give preference to any of the conditions based on the delay.
And you should be safe to take those 4-8 seconds after onset to
accomodate for sluggish HRF response.

But if you don't have them balanced, then you would have to go with
minimal size of delay, like in your case 1, but then you would probably
be out of luck, since the only response you would use, if there is such,
is the early raise or some pre-dip ;) might be not enough.

But why variable delay was chosen? ;)

just my few cents ;)

On Thu, 16 Jul 2009, Matthias Ekman wrote:
> Lets assume an experimental design looking like this:

> # Block I

> --REST

> # Block II

> --REST

> # Block III
> --REST
> ...

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