[Eeglablist] Pipeline of processing to optimize ICA for artrifact removal

[Spencer, Kevin M.]

Hi Scott,

In your comment below, would you please clarify whether the number of timepoints in the formula you give is the total number across epochs (so timepoints * epochs), or within each epoch? If the latter, that would suggest that it is better to run ICA on continuous data.

Like several users on this list, I sometimes encounter the problem that most of the ICs in a decomposition reflect a particular artifact class (e.g. eye blink) that usually, and ideally, would be represented by a single IC.

Thanks,
Kevin
________________________________________
From: eeglablist-bounces at sccn.ucsd.edu [eeglablist-bounces at sccn.ucsd.edu] On Behalf Of Scott Makeig [smakeig at gmail.com]
Sent: Thursday, February 23, 2012 11:33 PM
To: Arnaud Delorme
Cc: eeglablist at sccn.ucsd.edu; Kelly,    Edward *HS; Ross Dunseath
Subject: Re: [Eeglablist] Pipeline of processing to optimize ICA for    artrifact removal

Some additional >> comments,   Scott Makeig

On Thu, Feb 23, 2012 at 9:04 AM, Arnaud Delorme <arno at ucsd.edu<mailto:arno at ucsd.edu>> wrote:
Dear Mosdestino,

1. Difficulties with ICA. When removing ICA components, one of the main concern is the quality of your decomposition. We are currently working on tools to assess this quality although this can be tricky because of the large inter-subject variability. In the meantime, if you have multiple components for each type of artifacts, this is usually a sign that the quality of your decomposition is poor. One of the main factor to increase quality is to increase the amount of data and also high pass filtering if you have large offset in your data channels.

>> Modestino, you do not mention the data length he is using. An important value is #timepoints/(#channels)^2 ... this should be much more than 1 (even as high as 30 for 256 channels, in our (limited) experience -- I hope we will run a numerical experiment on this soon...  Running ICA on insufficient length data is the most common problem in applying ICA successfully.