Figure 9.

Distributed source estimates without functional magnetic resonance imaging (fMRI) constraints in the visual system. (Left) An indication of a percept is seen in early visual areas with help of frequency-tagged stimuli. Top plot shows a power spectrum with two clear peaks at each tagging frequency. Bottom plot depicts a time-frequency analysis with the white vertical line corresponding to the time at which there is a perceptual change. There is a clear shift in peak frequency of activity from one tagging frequency to the other (12 Hz–15 Hz) at this point in time. (Right) Change in the relative strength of activity in an occipital MEG sensor when the percept changes. Location and strength of activity is depicted on inflated lateral and medial brain surfaces in the left panel. White broken lines identify the calcarine sulcus, whereas white sold lines denote a region of interest. The right panel depicts amplitude ratios for stimuli at each tagging frequency. For details, see the text.