(A) Visual sensations (phosphenes) in the 4 visual field quadrants (delimited by a cross-hair) induced by (B). TMS over the occipital pole, online to simultaneous EEG-recordings from 45 scalp electrodes. (C) Time course of oscillatory α-band (8–14 Hz) activity (TSE) prior to TMS as a function of visual cortex excitability. (D) Scalp distribution of differences in α-band activity across the 4 windows of analysis. The TSE-waveforms are shown over a 1000-ms time window for all 45 scalp sensors (C: upper panel), and for the parieto-occipital (PO) and occipital (O) electrodes contralateral to the induced visual experience (data collapsed over electrodes, C: lower panel), that is, ipsilateral to the site of magnetic stimulation (see also B). Black lines correspond to those trials in which the participants reported perception of a phosphene induced by TMS (P-yes, high visual cortex excitability), gray lines represent those trials without perception of a TMS-induced phosphene (P-no, low visual cortex excitability). The gray area illustrates the time window of significant differences between trials (post hoc tests, Bonferroni corrected). Note that the most effective site for inducing phosphenes was localized for most individuals over the right hemisphere (n = 7, both left and right occipital poles tested). In only 2 participants it was easier to elicit stable phosphenes over the left hemisphere. The data of these 2 participants were flipped left–right for analysis and representation in this and all other figure.

Observed probability of same-percept repeats over all sessions (P-yes vs. P-no; black vs. gray bars) as a function of number of repeats (n = 0–15) and what would be expected based on a random, binomial distribution of P-yes and P-no responses (dashed bars). There was a high amount of single percepts (P-yes followed by a P-no report, or vice versa; i.e., n = 0 repeats) and much fewer same-percept repeats (e.g., n = 1 repeat: P-yes/P-no followed by another P-yes/P-no report). This provides evidence for yes/no-percepts and therefore perceptive states to alternate randomly on a subtrial-by-trial time scale (≤5 s). Whiskers represent SEs.

Time course of oscillatory α-band (8–14 Hz) activity prior to TMS over posterior recording sites contralateral to induced phosphenes, that is, ipsilateral to stimulation (line plots, data collapsed over same parieto-occipital (PO) and occipital (O) derivations as in Figure 1C gray frame) and proportion of P-yes and P-no trials (bar plots), as a function of ISI (A–E). The α-band changes leading to P-yes versus P-no percepts (associated with low vs. high visual cortex excitability) were not influenced by ISI, nor was the proportion of P-yes versus P-no trials, indicating independence from stimulus expectancy.