[FieldTrip] need example code - activity of condition 1 contrasted with condition 2.

[Johanna Zumer]

Dear Frank,

You're on the right way of thinking.   I think the answer partially depends
on your hypothesis.  In the tutorial situation of a Post and Pre, there is
the hypothesis that nothing of interest is going on in Pre, and that the
experimental manipulation is causing something to occur in Post, and the
researcher is asking how Post differs from Pre.

In your case of Left and Right, if you are assuming that these are equally
interesting experimental manipulations (i.e. neither is the 'baseline'
condition), then often the denominator is formed by the average of the two
conditions:

sourceDiff = sourceLeft_con;  % or sourceRight_con, does not matter
sourceDiff.avg.pow = (sourceLeft_con.avg.pow -
sourceRight_con.avg.pow) ./ (0.5*
sourceLeft_con.avg.pow +0.5* sourceRight_con.avg.pow);

Cheers,
Johanna





2013/2/7 Frank Mei <frank.ye.mei at gmail.com>

> Hi All,
>
> The tutorial here (http://fieldtrip.fcdonders.nl/tutorial/beamformer)
> provides example of activity contrasted with baseline, but not activity of
> condition 1 contrasted with condition 2.
>
> Could someone kindly give some example code that contrasts two activities,
> for example left vs right button pressing?
>
> I am thinking about modifying the example code in the tutorial, by turn
> the code
> -------
> sourceDiff = sourcePost_con;
> sourceDiff.avg.pow = (sourcePost_con.avg.pow - sourcePre_con.avg.pow) ./
> sourcePre_con.avg.pow;
> --------
> into A:
> --------
> sourceDiff = sourceLeft_con;
>  sourceDiff.avg.pow = (sourceLeft_con.avg.pow - sourceRight_con.avg.pow)
> ./ sourceRight_con.avg.pow;
> --------
>
> or into B:
> --------
> sourceDiff = sourceRight_con;
>  sourceDiff.avg.pow = (sourceRight_con.avg.pow - sourceLeft_con.avg.pow)
> ./ sourceLeft_con.avg.pow;
> --------
>
> Not sure if I should use "A" or "B", or something else.
>
> thanks,
> Frank
>
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