[Eeglablist] ERP analyses across groups with different latencies
k.whitehead at ucl.ac.uk
Wed Mar 20 23:33:29 PDT 2019
A Scientific Reports paper from our lab used a similar study design to your own (a within-subject condition and then the between-subjects factor is child/adult), you could have a look for ideas: DOI: 10.1038/srep28642
We often use Woody filtering (DOI: 10.1007/BF02474247) to align traces and correct for intra- and inter-subject small differences in latency, but your latency differences might be too big for this.
But we’ve also recently started using Thomas Koenig’s Ragu software. This software encourages you to check topographic similarity before comparing magnitudes (GFP in the case of Ragu). Because if the children and adults don’t have the same cortical source configuration of the ‘frontocentral N2’, then that is the more relevant way to compare them, rather than comparing amplitudes which actually derive from different sources.
UCL Dept. of Neuroscience, Physiology and Pharmacology
Tel: 020 7679 3533 (internal 33533)
From: eeglablist <eeglablist-bounces at sccn.ucsd.edu> On Behalf Of Mate Gyurkovics
Sent: 20 March 2019 12:26
To: eeglablist at sccn.ucsd.edu
Subject: [Eeglablist] ERP analyses across groups with different latencies
I am looking for "best practice" suggestions on how to deal with analyzing group differences in component magnitude when the two groups have different latencies and probably different latency jitter.
I have EEG data from two age groups (kids and adults), and I would like to look at the magnitude of the frontocentral N2 component across the two groups. I have a within-subject condition (conflict vs. no conflict trial) too, so what I'm mostly interested in is a Trial Type by Age Group interaction. I was originally planning on using mean amplitude but I ran into a problem, namely that the latency of the component is different between the two groups, so using the same time window to capture the N2 in mean amplitude in both groups seems difficult or impossible because if the window is broad enough to capture the wider peak of the younger group, it's too wide for the adults, and if it suits the adults, it's too narrow for the kids. I am reluctant to switch to peak amplitude because trial numbers are slightly different across conditions thus noise level differs too.
One option I considered is to create multiple shorter time windows and get the mean from each of those, and then add "Time" as a variable to my analyses, however the choice of time window lengths and number of time windows feels very arbitrary. I was also considering using an adaptive mean approach as that hopefully would be more robust to slight differences in noise level than a simple peak amplitude measure, but I'm not sure. What do you think? Any suggestions are welcome.
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