[FieldTrip] a few questions on separating fractal and oscillatory components in the data

[Schoffelen, J.M. (Jan Mathijs)]

Hi Ivaylo,

It seems that you have certain expectations about correlations that are not met by your data. I am not sure whether this warrants the conclusion that ’the separation fails with the default approach’.

It’s unclear what you correlate with each other, and why you expect these measures to be (linearly?) correlated or not. All in all this makes it hard to reply in a targeted fashion.

Regarding your statement of using medians for integration: this is what the irasa folks came up with, so it’s standard practice in the irasa universe.

Best wishes,
Jan-Mathijs


> On 23 Feb 2026, at 17:11, Ivaylo Iotchev via fieldtrip <fieldtrip at science.ru.nl> wrote:
>
> Dear community,
>
> this is a rather general question, because it is not limited to how IRASA is used within Fieldtrip, but whoever feels like answering feel free to tie your answers to Fieldtrip functions so that it is useful for everyone here.
>
> I came across the slope phenomenon rather recently, and the first general question is whether component separation always works and makes sense for every type of data? I noticed that my frequency specific components each remain positively correlated with the aperiodic part (and each other), strongly so (r > .90) thus I suspect that the separation failed with the default approach.
>
> For this reason I need to ask the legitimacy of a few alternative approaches, that make sense to me, but might be entirely wrong and I just don't see it
>
> 1. Divide the mixed spectrum by the aperiodic one, point by point. For me this reduces the correlation between oscillatory and aperiodic parts, but I do not see anyone else doing this
>
> 2. (in combination with the above) it seems to me that using medians to integrate power across bins is a good idea, but again this does not seem to be standard practice
>
> Just let me know what you think or know about this, and again feel free to incorporate Fieldtrip usage in your answer to make this more valuable for the community.
>
> Best wishes,
>
> --
> Dr. Ivaylo Iotchev. Researcher. Active in the fields of ethology, psychology, and neuroscience
> Eötvös Loránd University, Budapest
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