[Mne_analysis] ssp

[Kanal Eliezer]

You want to use as much data as you can, and the data should be as accurate a representation of the noise as possible. SSP, as described in the 1997 Uusitalo paper, works by defining a projection matrix consisting of all the noise in your data and then projecting that noise out. The more accurately your noise is represented in the projection matrix, the better a job SSP will do in de-noising your data. In almost all cases, I think, you're better off with more data. As to the minimum, I don't know of a definitive answer to that, but in our lab we've used data snippets as short as 30 seconds. Granted, at 1kHz, that's still 30,000 data points, but its not a lot of data relative to a 45-minute study.

Hope that helps -

Elli


--------------------
Eliezer Kanal, Ph.D.
Postdoctoral Fellow
Center for the Neural Basis of Cognition
Carnegie Mellon University
Pittsburgh, PA


On Jun 29, 2010, at 1:42 PM, Wiltrud Fassbinder wrote:

> I have a question about ssp. Participants in my study have a high rate 
> of artifacts (they are elderly), and we are exploring using ssp vectors 
> from a fun in which participants look at a dot of light for one minute 
> on the experimental condition data. Obviously there are tradeoffs here - 
> the more you apply vectors the more you probably also lose meaningful 
> data. My question is: When creating the ssp vectors, is it better to 
> create them from a longer segment or a shorter segment? Is there a 
> minimum amount of time that should be used?
> Thank you,
> Wiltrud Fassbinder
> 
> 
> Wiltrud Fassbinder, Ph.D.
> Adjunct Assistant Professor
> Communication Sciences and Disorders
> School of Health and Rehabilitation Science
> University of Pittsburgh
> 
> Research Associate
> Department of Audiology and Speech Pathology
> VA Pittsburgh Healthcare Center
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