averaging Hilbert amplitudes

[Adrian Bartlett]

Hi Karl,

In short, the former method gives you a mixture of time-locked power changes
and and the inter-trial phase coherence, since departures from perfect phase
locking will attenuate the amplitude of the average of your trials in the
time domain. Taking the hilbert amplitude envelope of single trials and then
averaging will yield the closest we can get the 'induced' response, or
time-locked power changes.
To reiterate, averaging in the time domain confounds power changes and phase
differences between trials. A good paper that touches on these topics is
Makeig et al. (2004) "Mining event-related brain dynamics".
I'm sure my comments on single-trial power as the 'induced' response will
cause a stir here, and if you look in the archives there are extensive past
discussions on the topic of isolating the 'induced' response from the
'evoked' (phase-locked)

Hope that helps some,

- Adrian M. Bartlett
Department of Psychology (MA Candidate)
Neuroscience Graduate Diploma Program
Perception & Plasticity Laboratory
Centre for Vision Research
York University
http://www.yorku.ca/~khoffman/

On Thu, May 20, 2010 at 2:41 PM, Karl Doron <karl.doron at gmail.com> wrote:

> Hello,
>
> I wonder if anyone can help me understand (or point me to a reference) the
> practical
> consequences of getting the analytic amplitudes of individual trials and
> then averaging those
> vs. averaging band pass filtered data, and then getting the analytic
> amplitude.
>
> Many thanks,
> karl doron
>
> ----------------------------------
> The aim of this list is to facilitate the discussion between users of the
> FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG
> and EEG analysis. See also
> http://listserv.surfnet.nl/archives/fieldtrip.html and
> http://www.ru.nl/neuroimaging/fieldtrip.
>

----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/neuroimaging/fieldtrip.
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