nf_prepdata

This function 1) mean centers each sensor/epoch of data, 2) removes quadratic trends, 3) applies a cosine-square taper to the beginning and final 5% of datapoints, and 4) makes the signal analytic (no power at negative frequencies) using the Hilbert transform, for each channel and trial of data. This preparation reduces spectral misspecification due to edge effects and quadratic trends. The function is called as follows:

EEG = nf_prepdata( EEG, center, detrend, taper, analytic );

Where EEG can be either 1) an EEGLAB-formatted (.set) data structure or 2) a data matrix of dimensions channels X time points X trials. The prepared data is returned in the .data field of the EEGLAB .set if an EEGLAB .set is the input, and the prepared data is returned in a matrix if a matrix is the input.