[Eeglablist] Contralateral and Ipsilateral waveforms

[Makoto Miyakoshi]

Dear Dwight,

I don't know what CDA stands for but I do have a paper about EEG study
using visual hemifield presentation so hopefully I understand what you
mean. It seems you are saying you don't see ipsi/contralateral presentation
effect. My understanding is that this effect is super robust and you should
not miss it. If, for example, you mixed up the event markers and randomly
choosing ipsi/contralateral event you can miss it. Another possibility
would be that stimulus presentation was too close to the central area AND
too dim AND too blurry; otherwise how can you destroy such robust effect?
Why don't you check these things first.

Makoto

2013/3/7 Dwight Peterson <dwight.peterson23 at gmail.com>

> Hi all,
>
>
>         For those of you familiar with the CDA, please help if possible.
>  I'm working on a project exploring the CDA for visual working memory and
> my data thus far show shockingly similar waveforms for contralateral and
> ipsilateral activity (my understanding is contralateral should be much
> higher in amplitude and negative going).  I have 4 different conditions in
> my experiment and I'm am including in my analysis only activity associated
> with CORRECT trials.  I have 7 channels with 6 electrode sites (Channel 1
> corresponds to a photo-diode that I use to mark the onset of my
> stimulus/trial).  I have these few sites b/c I'm working with an 8 channel
> "home-brew" sort of EEG system.   Ch 2 = P7, Ch 3 = P8, Ch 4 = PO7, Ch 5 =
> PO8, Ch 6 = P1, Ch 7 = P2.
>
>          I've created an event list that creates 8 bins that correspond to
> Left Hemifield trials and Right Hemifield trials for each of my 4
> conditions that correspond to my event type (unique identifier values) as
> shown below:
>
>    70       "ss_two_r"     1   "two_objects_RVHF"
>
>    71       "ss_two_l"     2   "two_objects_LVHF"
>
>    80     "ss_three_r"     3 "three_objects_RVHF"
>
>    81     "ss_three_l"     4 "three_objects_LVHF"
>
>    90 "ss_three_apart_r"     5 "three_objects_apart_RVHF"
>
>    91 "ss_three_apart_l"     6 "three_objects_apart_LVHF"
>
>    94 "ss_three_prox_r"     7 "three_objects_prox_RVHF"
>
>    95 "ss_three_prox_l"     8 "three_objects_prox_LVHF"
>
> Then after epoching, running artifact detection, and computing averaged
> ERP waveforms for each of these bins, I created a new ERPset from Bin
> Operations using the Independent Transformations "mode" with the following
> formulas to extract the contralateral and ipsilateral waveforms:
>
> LH = [2 4 6]
>
> RH = [3 5 7]
>
> nb1 = 0.5*b1 at LH + 0.5*b2 at RH label average contra two objects
>
> nb2 = 0.5*b1 at RH + 0.5*b2 at LH label average ipsi two objects
>
> nb3 = 0.5*b3 at LH + 0.5*b4 at RH label average contra three objects
>
> nb4 = 0.5*b3 at RH + 0.5*b4 at LH label average ipsi three objects
>
> nb5 = 0.5*b5 at LH + 0.5*b6 at RH label average contra three apart
>
> nb6 = 0.5*b5 at RH + 0.5*b6 at LH label average ipsi three apart
>
> nb7 = 0.5*b7 at LH + 0.5*b8 at RH label average contra three prox
>
> nb8 = 0.5*b7 at RH + 0.5*b8 at LH label average ipsi three prox
>
>
> Then I get the CDA difference waveforms for each condition by recursively
> updating the new Contra Ipsi ERPset by using the following formula
>
> b9 = b1-b2 label CDA Two Objects
>
> b10 = b3-b4 label CDA Three Objects
>
> b11 = b5-b6 label CDA Three Apart
>
> b12 = b7-b8 label CDA Three Prox
>
>        Perhaps I am just seeing an extremely NULL result and lack of a
> difference between contra and ipsi waveforms for each condition, but I've
> tried a variety of things and double checked these formulas (which seem to
> be correct given my event types and bins, etc.).    Impedances are below 5 KΩ
>  and aside from the lack of a difference between contra and ipsi, the data
> looks pretty clean.
>
> For anybody who has done this type of research before, do you have any
> thoughts?
>
> Thanks so much!!!
>
>
> --Dwight--
>
> --
> Dwight J. Peterson, M.A.
> Graduate Assistant
> Cognitive and Brain Sciences
> Department of Psychology/296
> Memory and Brain Laboratory
> University of Nevada, Reno
> Reno, NV 89557
> Cellular: 319-231-8596
> Laboratory: 775-682-8667
>
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-- 
Makoto Miyakoshi
JSPS Postdoctral Fellow for Research Abroad
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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