[FieldTrip] gamma oscillations, how to prove they are (not) there

[Rojas, Don]

Ben,

Gamma oscillations are tiny and the 1/f characteristic normally obscures them in fft plots. I don't think that gamma is a particularly convincing oscillation that you would expect to see in a raw waveform because 1) it is so small and 2) it is a rather broad band that doesn't look like a sinusoid. Since you have two conditions to compare, one of which you expect to see greater gamma for, use ft_math to create a difference spectrum, which will remove much of the 1/f characteristic and emphasize the condition differences. Also, if you don't see condition differences, you can try computing the same thing for post-stimulus vs. pre-stimulus fft. The same logic would apply to your spectrograms.

Best,

Don

On Oct 17, 2013, at 10:20 AM, "van Lier  Ben" <ben.vanlier at bsse.ethz.ch> wrote:

> Hi all,
> 
> I am trying to show an increase in gamma oscillations. According to literature they should be there without a doubt. But, I am not too sure about the actual recording - i have the feeling i was just recording noise.
> 
> When i eyeball raw traces, i do not see a difference between condition 1 and 2. Same for the PSD and spectrograms, just the 1/f noise.
> 
> My question is, could there still be (eg low amplitude) oscillation in the data that you just wont see by eye? what is your experience in this?
> 
> Using freqstatistics, some channels do show significance but im a bit skeptical. I have been playing around with freqstatistics and simulated data from freqsimulation and the stats only made sense when i could clearly see it by eye in the spectrogram as well...
> 
> Cheers,
> Ben
> 
> 
> 
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