V1 time-courses were examined for changes in alpha-gamma phase amplitude coupling (PAC). The general procedure is outlined in Figure 2. The first step was to obtain estimates of low frequency phase (fp) and high frequency amplitude (fa) for each trial using a fourth order, two-pass Butterworth filter, and then applying the Hilbert transform (Le Van Quyen et al., 2001). To avoid sharp edge artifacts, which can result in spurious PAC (Kramer et al., 2008), the first 500 ms and last 500 ms of each trial was discarded.
