UC Santa Cruz

Despite a large body of research indicating that alpha oscillations are involved in visual processing, and particularly that alpha frequency relates to temporal resolution and discriminability of stimuli, the mechanisms underlying exactly how alpha shapes our conscious perception is still unclear. According to one account, perception could be discretely windowed by each alpha cycle into a series of “snapshots” (discrete sampling theory), while another account posits that just the strength of perception continuously waxes and wanes across each alpha cycle (rhythmic sampling theory). This dissertation examines features of alpha oscillations in the context of these theories of perceptual sampling. We demonstrate that perception is unlikely to occur in discrete snapshots, given that an individual’s alpha frequency (IAF) does not relate to the magnitude of their percepts across similar visual illusions that are thought to depend on discrete sampling, nor does it relate to the timing of sensory responses associated with visual percepts. Finally, we find that alpha does not relate to a bias in duration estimation, which should occur if individuals accumulate varying amounts of visual information via discrete perceptual snapshots due to their varying IAFs. However, we found support for the role of alpha oscillations in modulating the strength of our sensory percepts by demonstrating that alpha phase – and its interaction with alpha power – relates to the strength of sensory responses associated with visual perception, and that IAF relates to individual differences in sensitivity when estimating and discriminating the durations of visual events. These studies provide novel insights into how alpha oscillations play a role in visual processing, not just around the timing of a single alpha cycle, but also at longer durations of stimulus processing in a way that facilitates our perception of time.