To identify the anatomical origin of the neural populations generating these sensor-level time–frequency responses, a beamforming approach was utilized. We used a pre-stimulus baseline period of equivalent duration and bandwidth to the target windows identified in the sensor level analysis to each window of interest (baselines: theta: − 300 to − 50 ms, alpha: − 300 to − 50 ms, gamma: −300 to 0 ms). The resulting functional maps were averaged across the entire sample in order to identify the specific location of visual-spatial neural oscillatory activity. Mapping of both the theta response and the gamma response revealed two (bilateral) clusters in medial occipital cortices near primary visual cortices. In contrast, alpha oscillatory activity showed two (bilateral) clusters in more lateral occipital cortices, near visual association areas (Fig. 1b).
