"Rhythms of visual perception and attention"
Neuronal communication between cortical areas heavily relies on oscillatory, periodic mechanisms whose precise timing critically determines the flow of information. Yet little is known about the perceptual and psychological consequences of such periodic neuronal dynamics. I will show several examples of these perceptual consequences. In the "wagon wheel illusion", a continuously moving object seems to reverse sporadically: this can be explained by assuming that motion perception relies on a series of perceptual episodes or "snapshots" taken at a rate of ~13Hz. This periodic sampling of motion information depends on attention, as it vanishes when attention is distracted. In another EEG study, we showed that the probability of detecting a dim peripheral flash of light directly depends on the phase of ongoing brain oscillations at ~8Hz, shortly before the flash onset. Again, this effect was strongly linked to attention. More recent experiments suggest that alpha rhythms implement a ~10Hz perceptual "echo" of the internal representation of visual stimuli. This 10Hz reverberation is rendered visible as a striking illusion of flicker on a purely static stimulus. To summarize, perception and attention seem to wax and wane intermittently, possibly as a reflection of underlying periodic processes.