Figure 1.
Prepulse phase predicts phosphene perception. A, Statistical comparison between phase-locking values for trials grouped according to perception (phosphene/no-phosphene, averaged over 64 electrodes and 9 subjects) and surrogate phase-locking values computed over random subsets of trials. A significant effect indicates that ongoing phase differs statistically for phosphene and no-phosphene trials. The color map represents uncorrected p values (similar in B and C) and the white outline indicates significant effects corrected for multiple comparisons using the FDR method. There is a strongly significant phase effect (FDR = 10−5; corresponding to a p value threshold of 6.4 × 10−7) in the last 400 ms preceding the pulse, ranging in frequency from 7 to 17 Hz. The topography shows the scalp distribution of phase-locking values in the time–frequency range of 7 to 17 Hz and −400 to −50 ms. Further analyses are performed on two regions of interest: a frontal and an occipital one. B, Statistical significance of the phase difference between phosphene and no-phosphene trials, in the frontal region of interest at each time–frequency point. There is a strongly significant phase effect (FDR = 10−3; corresponding to a p value threshold of 6.2 × 10−5) in the 400 ms preceding the pulse and in the alpha frequency range (∼10 Hz). C, Same as B, but for the occipital region of interest.