[Eeglablist] help with group-level interactions between variables in LIMO EEG

Jasna Martinovic J.Martinovic at liverpool.ac.uk
Wed Sep 3 04:31:39 PDT 2014


hi,

I've got a design in which participants categorise three types of 
images, which are displayed with three different types of contrast 
(luminance and two chromatic types of contrast). LIMO EEG seems to be 
ideal for analysing this data, as it allows for continuous variables to 
be included in the design.

On the single subject level, I have created a design matrix which suits 
my study, with 3 levels of my first factor as categorical and then the 
three continuous variables in addition to that. I get 1 categorical 
effect and 3 covariate effects for each subject.

At group level, I have obtained the effects of the 3 co-variates on the 
ERP and they look very sensible, as one would predict it.

What I would still like to do is this:
1) check for partial correlations between my three covariates, to see 
how independent they are of each other, preferrably at the group level.
2) check if the covariates interact with the categorical variable, again 
preferrably at the group level.

If it is not possible to do this at group-level, then I would be happy 
to conduct these analyses on single-subject level and generalise from it.

I have unfortunately failed to figure out how to do so in LIMO, even 
after looking at the tutorial and looking at some published manuscripts.

I look forward to receiving some advice here.

Thanks in advance,
Jasna


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