Due to prior interest in the gamma and alpha-bands (Hoogenboom et al., 2006; Muthukumaraswamy et al., 2010; Michalareas et al., 2016), the visual data were band-pass filtered (Butterworth filter) between 40–60 Hz (gamma) and 8–13 Hz (alpha), and source analysis was performed separately for each frequency band. To capture induced rather than evoked visual activity, a period of 300–1,500 ms following stimulus onset was compared with a 1,200 ms baseline period (1,500–300 ms before grating onset). The change in oscillatory power for each vertex was averaged across participants, interpolated onto a 3D mesh provided by the Human Connectome Project (Van Essen, 2012), and thresholded at a value which allowed the prominent patterns of power changes to be determined (see Figure 3, script: 2_get_source_power.m).
