Dear Sahil,
The error may occur during the wavelet-minimum description length (MDL) process. The wavelet-MDL method uses the explanatory variable to decompose the near-infrared spectroscopy (NIRS) signal into low-frequency drift and hemodynamic signal. Here, the explanatory variable represents the predicted NIRS response induced by stimulus or task. Therefore, to remove the low-frequency drift from your resting-state NIRS data, you may want to use a high-pass filter.
A high-pass filter based on a discrete cosine transform (DCT) is currently implemented in SPM, and is available in the SPM for NIRS toolbox. To resolve the problem, in the step of 'specify 1st level', please select the DCT-based high-pass filtering.
Yours sincerely,
Sungho
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Wellcome Trust Centre for Neuroimaging
University College London
12 Queen Square
London WC1N 3BG
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