Publication
Alpha oscillations represent the brain's electrical activity in the frequency range of 8 to 13 Hz. They are often considered to be the rhythm of conscious perception, rhythmically modulating the processing of sensory inputs. This interpretation has been driven by experimental findings indicating that ongoing alpha oscillations can account for perceptual fluctuations and, more crucially, that the speed of the alpha frequency predicts the temporal resolution of visual perception.
However, the theory that alpha oscillations, at each cycle, sample visual information into discrete conscious percepts raises some concerns. First, while studies on the temporal resolution of visual perception provide information about what is consciously perceived, they cannot conclusively demonstrate when a discrete conscious percept emerges. Second, the cycles of alpha oscillations, lasting about 100 milliseconds, cannot explain the existence of windows of integration extending over several hundred milliseconds. In this thesis, I therefore question whether alpha oscillations truly determine the temporal structure of consciousness per se. In particular, I investigate whether alpha oscillations demonstrate long-lasting effects in sensory processing, which would offer an alternative explanation to their role in visual perception.
Based on theoretical considerations, I begin by characterizing the missing links that relate oscillatory rhythmic effects to discrete perception. I then argue that alpha oscillations do not determine the temporal structure of consciousness but, instead, influence sensory processing, which in turn can modulate the content of consciousness. This proposition is supported by two studies demonstrating long-lasting contributions of alpha oscillations to visual processing, beyond the temporal resolution of a single alpha cycle. In the first study, I show that pre-stimulus alpha activity can modulate the unconscious integration of visual features presented over a few hundred milliseconds. In the second study, I provide evidence that the dominant alpha frequency predicts the ability to segregate two visual stimuli, even when they are presented in two successive alpha cycles. Finally, these results are complemented by a third study, in which I investigate the neural entrainment of alpha oscillations using rhythmic visual stimulation, providing additional evidence of long-lasting changes in oscillatory dynamics that extend well beyond the stimulation.
Taken together, these findings contribute to our understanding of the role that alpha oscillations play in visual processing, offering new evidence of their functional implications over longer durations than previously suggested.