[Eeglablist] Creating ERPs contralateral and ipsilateral to stimulus presentation

[Bradley Voytek]

Daniela:

I think I'm the one that wrote that message?

So let's say that you want to normalize your plots such that all
stimuli "appear" in the right visual hemifield and let's say channel
25 is over the left visual cortex and channel 62 is over the right.

When a stimulus appears in the right hemifield, you just look at
activity in channel in the contralateral visual cortex, so you look at
channel 25. But if the stimulus appears in the left visual hemifield
you want to look at channel 62.

So for all trials where stimuli appear in the left visual hemifield,
just swap channels from the left hemisphere to the right and vice
versa.

So, for example, you might say:

tempLeft = EEG.data(25, :);
tempRight = EEG.data(62, :);

EEG.data(25, :) = tempLeft;
EEG.data(62, :) = tempRight;

clear tempLeft tempRight


(note the above code was just typed from memory in this email without
checking it, but hopefully you get the idea).

::brad




On Sun, Jan 29, 2012 at 12:55, Daniela Gledhill
<d.gledhill at uni-bremen.de> wrote:
> Dear all,
>
> I am doing my PhD in Visual Neuroscience and quite recently started my EEG
> analysis with EEGLAB.
> In my experiment two stimuli are presented bilaterally with one of them
> changing it's color. I am trying to create ERPs contra- and ipsilateral to
> the color change, but not sure how to proceed in EEGLAB.
>
> There is only one message in the discussion list with the idea of "Swap the
> data, not the channels. Leave the channels alone."
> But how does it work?
> - contralateral:  data of left-hemispheric electrodes for changes on the
> right side and data of right-hemispheric electrodes for changes on the left
> side
> - ipsilateral:  data of left-hemispheric electrodes for changes on the left
> side and data of right hemispheric electrodes for changes on the right side
>
> It would be wonderful to get some help with that!
>
> Kind regards from Bremen,
> Dani
>
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