Data preprocessing and feature extraction:
Data preprocessing steps are described at length in prior workNext, DToFs underwent dimension reduction by considering their zeroth, first and second moments (i.e. sum, mean, and variance)To convert the preprocessed DToF moments data to relative changes in oxy- and deoxy-hemoglobin concentrations (HbO and HbR, respectively), we used a sensitivity method described in detail previouslyLastly, only channels that were formed between sources and detectors both within the prefrontal regions were considered for subsequent analyses.