Article Figures & Data
Figures
- Figure 1.
Radial and spiral hallucinatory patterns are preferentially elicited by flicker at distinct frequencies. A, Probability of occurrence of each hallucinatory pattern in relation to flicker frequency. Error bars represent SEM across observers (N = 8). Thick background lines represent the best-fitting Weibull function to the grand-average data, with vertical arrows pointing to the corresponding peak frequency on the x-axis. Each colored vertical line in the background denotes the peak frequency for reporting a radial (blue line) or a spiral pattern (red line) of an individual subject (line thickness indicates the number of subjects with the same peak frequency). The difference in peak frequency was statistically significant across observers (paired t test, t(7) = 9.5, p < 0.00003). B, Difference between report probabilities of the two shapes (black line; error bars represent SEM across observers). The shaded gray area indicates the mean difference (±SEM across observers) between Weibull-function fits of individual subjects. The minimum and maximum frequencies for this difference are 4 and 17 Hz, respectively. Each colored vertical line in the background denotes the minimum (blue line) and maximum (red line) frequencies of an individual subject (line thickness indicates the number of subjects with the same frequency).
- Figure 2.
Radial and spiral images preferentially enhance distinct brain oscillatory frequencies. A, Facsimile versions of the radial and spiral hallucinatory patterns. These two images, equalized for low-level properties, were presented statically for 12 s while EEG responses were recorded. B, ERPs to trial onset revealed that differential activity between radial and spiral images was restricted to occipitotemporal sites (scalp-topography time line on top) and at relatively long latencies (peaking at ∼170 ms). The background grayscale indicates significance of a paired t test across observers (N = 20; p < 0.05, FDR-corrected for multiple comparisons across electrodes and time points). The enlarged scalp map illustrates the topography at the time of maximal difference. The two highlighted points on this map mark the electrodes on which the ERP displayed underneath was computed, and which were selected for further analysis. C, Spectral power differences between EEG signals recorded during static viewing of radial versus spiral images. The background colors indicate significance of a paired t test across observers (p < 0.05, FDR-corrected; strongest color for p < 0.02, FDR-corrected), with blue denoting frequencies of higher power for radial images (peaking between 4 and 6 Hz) and red higher power for spiral images (peaking between 11 and 21 Hz).
