Hi, Sam-
Using ZERO in 3dTproject would not be good enough. The issue is that the typical way of estimating spectral power (or amplitude) distributions is via the Fourier Transform (FT, or Discrete Fourier Series (DFT)). To use the FT, the time series data must be regularly sampled. Inserting zeros means that the length of time series doesn't change, but those would be interpreted as values of the time series and used in the FT-- that would change the spectrum a lot, for residual time series like resting state likely increasing the relative power of low frequencies artificially.
Using NTRP might be a bit better in some sense, but it would still likely lead to a bias toward low frequencies (if the interpolation is low order) or potentially some artificial high frequencies. It might be hard to predict the effect here, but the main thing is that one is still "tampering" with the final power spectrum, changing its values solely by the censoring processing.
What one would prefer would be to ignore those censored time points (which is different than using them with a value of 0 or of an interpolated value), and estimate the power spectrum of just the time series points that were not censored. The issue *there* is that once censoring has occured, the remaining time series is no longer regularly/uniformly sampled (because there gaps chopped out of it). Fortunately, astrophysicists were having to struggle with this a while back because their time series of astronomical observations would get interrupted by moving planets, moons, clouds, etc. A number of people worked on this, but the ones who get hte most credit are Lomb and Scargle in the late 1970s/early 1980s, who worked out an approach that was equivalent to classical FT results if the data were uniformly sampled, and then a reasonable extension with similar statistical properties when the data were *not* uniformly sampled. There has been further work on this still, using further adaptations of their work and other ones (here is an excellent one, if you are interested: [
arxiv.org]).
--pt
