The degree to which each participant showed phase coherence over trials was calculated by computing an inter-trial phase coherence (ITPC) measure. ITPC is a frequency domain measure that indicates the degree to which EEG activity is phase-locked, across trials, to specific experimental events – in this case presentation of the 8 cycles/degree Gabor patch. The power spectrum of each trial was calculated using a hanning tapered fast Fourier transform with a window size of 128 ms. α-Band power was dominant in the signal following stimulus presentation, therefore inter-trial α phase coherence, specifically at 11.7 Hz, was calculated using the newtimef function in EEGLAB. The highest ITPC value within the 100–170 ms post stimulus onset time-window was extracted for each participant to give an indication of the maximum level of ITPC, a high level (up to 1) indicates strong phase coherence, i.e., low variability; a low level (down to 0) indicates weak phase coherence, i.e., high variability. In addition, ITPC was calculated across the time-series.
