[Eeglablist] ERP grand average does not reflect actual latency

Shih-Chun Kao shihchunkao at gmail.com
Tue Mar 28 14:16:39 PDT 2017

Thank you for the references, Daniele! The latency was point based using a
local peak approach. I looked grand average for each subject individually
but it seemd that I did not really have spike points. Instead, I have some
subjects showing strong slow wave in one condition than others. Some
subjects also have larger area under the P3 curve in one condition than
others. I wonder if the inconsistency between grand average and actual
latency measures could happen when one condition has more vaiant peak
latency and differnet shape of P3 (e.g. area nuder the curve) than others?
Regardless, I will definitely read those papers and try to figure it out
what happends to my dataset.


On Tue, Mar 28, 2017 at 2:09 PM, Daniele Marinazzo <
daniele.marinazzo at gmail.com> wrote:

> Dear Alvin
> focusing only on a tiny part of the erp, and only on the average, is not a
> good way to analyze the data, since it makes too many assumptions on the
> underlying distribution of data, individual variability, and on the ERP
> time course as a whole.
> Guillaume Rousselet, Cyril Pernet and others have explained this in great
> detail, with code and examples, see for example these papers
> http://onlinelibrary.wiley.com/doi/10.1111/ejn.13400/full
> http://biorxiv.org/content/early/2017/03/27/121079
> and in these blog posts with code
> https://garstats.wordpress.com/2016/07/28/neuroscience-group-results/
> https://garstats.wordpress.com/2016/04/02/simple-steps-
> for-more-informative-erp-figures/
> https://garstats.wordpress.com/2016/07/28/neuroscience-group-results/
> hope this helps
> Daniele
> On Tue, Mar 28, 2017 at 3:30 AM, Shih-Chun Kao <shihchunkao at gmail.com>
> wrote:
>> Dear list,
>> If I found a statistically significant P3 latency effect (~50ms) between
>> two conditions in a within-subject design study but my grand average plot
>> does not show such difference, what would be the cause for inconsistent
>> results and what does such inconsistency suggest? I understand grand
>> average is not the best illustration but I thought 50ms is a pretty big
>> difference. Thank you!
>> Alvin
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Shih-Chun Kao (Alvin)
Neurocognitive Kinesiology Laboratory
Department of Kinesiology and Community Health
College of Applied Health Sciences
University of Illinois at Urbana-Champaign
skao5 at illinois.edu
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