[FieldTrip] Oscillatory power normalization

[smoratti at psi.ucm.es]

Hi Matt,

I think Fieltrip does not do these transformations. However you could do cfg.baselinetype = 'relative' (power post/power pre) and take the log10 and multiply by 10 (TF.powerspctrm). Then you should have dB.

best,

Stephan

________________________________________________________
Stephan Moratti, PhD

see also: http://web.me.com/smoratti/

Universidad Complutense de Madrid
Facultad de Psicología
Departamento de Psicología Básica I
Campus de Somosaguas
28223 Pozuelo de Alarcón (Madrid)
Spain

and

Center for Biomedical Technology
Laboratory for Cognitive and Computational Neuroscience
Parque Científico y Tecnológico de la Universidad Politecnica de Madrid
Campus Montegancedo
28223 Pozuelo de Alarcón (Madrid)
Spain


email: smoratti at psi.ucm.es
Tel.:    +34 679219982

El 23/04/2012, a las 05:54, Matt Mollison escribió:

> Hi FieldTrippers,
> 
> In almost all the papers I've read involving oscillatory power, some kind of transformation is done to the data due to the 1/f power spectrum effect (power decreases as frequency increases). I'm mostly looking at within-subjects experiments (every subject behaved in all conditions) comparing conditions across subjects, but it seems like normalizing the power spectrum should apply in any case (especially if any kind of parametric stats are done—right?).
> 
> Anyway, it's not apparent to me how to use FT functions like ft_freqanalysis to make these transformations (e.g., log10 normalization, dB normalization [EEGLab does this], vector length normalization, etc.; the only thing I see is in ft_sourcedescriptives, but I'm not doing source analyses), and it confuses me why this is the case. I can't find much discussion regarding the 1/f issue on the FT wiki or the mailing list. This seems like an important step that is missing from any frequency analysis workflow. Am I missing something (meaning I just don't see the option), am I misunderstanding something (meaning I'm incorrect in this assumption), or is this an issue that needs to be fixed?
> 
> Thanks,
> Matt
> 
> --
> Univ. of Colorado at Boulder
> Dept. of Psychology and Neuroscience
> matthew.mollison at colorado.edu
> http://psych.colorado.edu/~mollison/
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