[Eeglablist] topoplot methods

[Stephen Politzer-Ahles]

Hi Josh,

As for (1), setting the 'shading' parameter to 'interp' makes the plot
look less pixellated, if that's what you're looking for. Here's an
example I made: http://i.imgur.com/fMgeXTt.png .

As for (2), there might be a simpler way to do this... but as a
nonelegant way, you could just calculate a matrix representing the
interaction term (in channels*timepoints) and use that as input to
topoplot(). I haven't tried this by myself, but for instance if your
conditions at Ia, Ib, IIa, and Ib (and each of those is a
channels*timepoints matrix), then I guess something like this should
work:

---

% some simple effects
effect_of_a_vs_b = Ib - Ia;
effect_of_I_vs_II = IIa - Ia;

% expected value of IIb if there were no interaction
expected = Ia + effect_of_a_vs_b + effect_of_l_vs_ll

% Interaction
interaction = IIb - expected

% vector of values to plot
range = mean( interaction(:,
beginning_of_timewindow_of_interest:end_of_timewindow_of_interest),
2);

% plot it (assuming 'locations' has already been loaded)
topoplot(range,locations, ..... );

---

The matrix "interaction" represents how much bigger (or smaller) the
signal is in condition IIb than you would expect if the two effects
were purely additive. But like I said, there might be a more
straightforward (and/or statistically smarter) way to do this.

Best,
Steve



On Fri, Feb 1, 2013 at 9:15 PM, Joshua Hartshorne
<jkhartshorne at gmail.com> wrote:
>
> Two questions about topoplot():
>
> 1) Can I change the smoothness/granularity of the topoplot?
>
> 2) Can I plot the topographic distribution of a 2x2 interaction? I can get the pvalues plotted topographically, but not the voltages.
>
> Many thanks,
> Josh Hartshorne
>
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--
Stephen Politzer-Ahles
University of Kansas
Linguistics Department
http://people.ku.edu/~sjpa/