[Eeglablist] triangular / sawtooth / zig-zag pattern in spectral data
bachman at psych.ucla.edu
Mon May 12 10:53:24 PDT 2014
When I plot spectral data from continuous EEG, the resulting Power-by-Frequency graph looks very strange. Specifically, starting at about 5 Hz and continuing on to higher frequencies, the plots for each channel have a repeating triangular, or sawtooth-like, or zig-zag shape.
Here is a Dropbox link to an image of representative data: https://www.dropbox.com/s/lddxgzlti9m20vj/FFT_triangle_pattern.JPG
It looks like some kind of wacky filter has been applied, but the only filter in the processing pipeline is a very conventional 0.16-100 Hz bandpass.
The problem isn't a feature of the raw data itself, because opening the same continuous data in different EEG analysis programs and applying a FFT produces very normal looking spectra. This happens across different versions of EEGLAB, Matlab, and Windows.
The continuous data were recorded using a Biosemi system and saved in .bdf format.
Has anyone run into this before? I’d be very grateful for any suggestions.
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the eeglablist