[Eeglablist] .datersp file contents question

Mikołaj Magnuski imponderabilion at gmail.com
Wed Feb 26 04:42:45 PST 2014


Hi Steven,

by default spectra and ersps computed in EEGlab are transformed to dB (10 *
log10( power ) ).
erspbase should represent baseline (in dB too) that was subtracted from
each time step of your ersp. The baseline is mean spectrum in time range
that you defined when precomputing (by default it is everything before time
zero).
This means that ersp fields contain baseline-corrected time-freq
representation in dB.
(if I am not correct about ersp or erspbase fields, please correct me,
eeglablist).
25 lut 2014 22:18 "Steven Pillen" <stevendpillen at gmail.com> napisał(a):

> Hello, EEGLAB list.
>
> We were running an ERSP study, and we had some questions about the output
> files.
>
> When we load the contents of a .datersp file with the function, "m =
> importdata('filename.datersp'), the m struct contains two elements for each
> channel:
>
>  chan1_ersp: [100x200 single]
>  chan1_erspbase: [1x100 single]
>
> I figure that the two dimensions of the plain "ersp" correspond to
> frequency and time respectively, because they are the same size as the
> m.freqs and the m.times branches.  What I am unsure of is what exactly I am
> looking at in the contents of these files.  Can anyone tell me what the
> numbers in those branches represent?
>
> I was hoping, for instance, that the values in the "ersp" branch would
> contain a table of the spectrum values for each cross-section of frequency
> and time, but it looks like maybe they've had some kind of normalization
> applied to them, like maybe a logarithmic function or something.  I want to
> be sure what I'm looking at before I attempt any statistical analysis.
>
> Also, what is the relationship between the "ersp" and the "erspbase"?
>
> Thank you,
> Steven Pillen
>
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