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Preservation of alpha rhythm shortly after photic driving.

EEG responsiveness to intermittent photic stimulation (IPS) with repetitive flashes was examined just after the pause of IPS. By omitting 5, 10, 15 and 20 flashes in the course of IPS at 10 Hz, 2 s IPS responses at the midline occipital area were compared between flash trains before (train 1) and after the pause (train 2). Amplitude, peak frequency and bandwidth (reflecting the degree of rhythmicity) of an alpha peak in the power spectrum of averaged IPS responses were each obtained every 50 ms with the power spectrum based on a time-varying AR model. Bandwidth was more sensitive to IPS responses, because significant differences in bandwidth between trains 1 and 2 occurred earlier than differences in amplitude. There were greater differences in bandwidth for the omission of 5, 10 and 15 flashes, suggesting increased responsiveness to train 2, while there were no significant differences in bandwidth for the omission of 20 flashes. These findings show that rhythmicity in IPS responses can be preserved up to 1.6 s after the pause of IPS.