[pymvpa] Interpreting representation similarity results

[Vadim Axel]

Thanks for the answer.

Suppose, I can similarity between two tasks  a) only in specific region,
but not other regions and b) do not get similarity in this region when I
use some control task. Do you see a trivial, non-cognitive explanation to
this?

Thanks for refs. So, you show that vision and action have similar neural
representation. Representation is obviously the straightforward
interpretation, whereas cognitive processing is a next step.  In my case, I
have also baseline because I check similarity between A > baseline1 is
similar and  B > baseline2. But conceptually, I think  it is all the same.


On Thu, Aug 20, 2015 at 2:18 PM, Nick Oosterhof <
n.n.oosterhof at googlemail.com> wrote:

>
> > On 20 Aug 2015, at 10:59, Vadim Axel <axel.vadim at gmail.com> wrote:
> >
> > Very simple question: to what extent representation similarity can be
> interpreted as similarity of cognitive processing?
> >
> > Consider a toy sample, where I have two experiments. In Exp.1 there is
> task A and baseline1. In Exp.2 there there is task B  and baseline2. For
> each experiment, I generate t-contrasts:  A > baseline1 and  B > baseline2.
> To check for similarity between tasks A and B, I can run conjunction
> analysis (spatial overlap). For stronger evidence, I can for each
> experiment, extract t-values for some predefined ROIs. Then, I run Pearson
> correlation across voxels within a ROI. Using across subjects statistics I
> can show that in some ROIs the correlation between experiments is above 0.
> Can this result be interpreted, as having similarity of cognitive
> processing during two tasks?
>
> It would indicate that *something* is similar (at a pattern level) between
> the two tasks. You may possibly interpret this as cognitive processing, but
> cognitive processing is a rather broad concept. Pattern similarity can
> arise through a variety of different mechanisms, including trivial ones.
>
> > Also, does someone know about papers that examined similarity between
> experiments using a contrast (and not Haxby_2001_like_style of patterns of
> single faces vs cats). In my case, Exps 1 and 2 have very different
> designs, so A and B cannot be compared directly. In general, good
> references for citing are highly appreciated.
>
> This may be considered as shameless self-promotion, but I have done some
> work on executing versus observing different manual actions [1], and
> imagery and execution/observation of such actions [2].
>
> [1] Oosterhof, N. N., Wiggett, A. J., Diedrichsen, J., tipper, S. P. &
> Downing, P. E. Surface-based information mapping reveals crossmodal
> vision-action representations in human parietal and occipitotemporal
> cortex. J. Neurophysiol. 104, 1077–1089 (2010).
> [2] Oosterhof, N. N., Tipper, S. P. & Downing, P. E. Visuo-motor imagery
> of specific manual actions: A multi-variate pattern analysis fMRI study.
> Neuroimage 63, 262–271 (2012).
>
>
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