Artifacted EEG epochs for each subject were transformed into reference-free current source density (CSD) estimates (μV/cm2 units; 10 cm head radius; 50 iterations; m = 4; λ = 10−5; 29) using a spherical spline surface Laplacian (26; 45; Matlab-based CSD toolbox and tutorial 47). The mean offset of each epoch was eliminated, a 50% Hanning taper window applied, and zeros padded to the beginning and end of each epoch to yield power spectra with a resolution of .25 Hz (i.e., 4 s at 1024 points/epoch). Averaged power spectra were then computed (48) for each condition (closed/open), and converted to amplitude spectra by square root transformation (i.e., RMS). After eliminating the first (DC) point, the next 299 points were used in subsequent analyses (i.e., .25 – 74.75 Hz).
