Perception of near-threshold visual stimuli is influenced by pre-stimulus alpha-band amplitude but not by alpha phase

Abstract

Ongoing brain activity preceding visual stimulation has been suggested to shape conscious perception. The underlying mechanisms are still under adebate,lthough alpha oscillations have been pointed out as the main explanatory candidate. According to the pulsed-inhibition framework, bouts of functional inhibition arise in each alpha cycle, allowing information to be processed in a pulsatile manner. Consequently, it has been hypothesized that perceptual outcome can be influenced by the specific phase of alpha oscillations prior to the stimulus onset, although empirical findings are controversial. In this study, we aimed to shed light on the role of pre-stimulus alpha oscillations in visual perception. To this end, we recorded electroencephalographic (EEG) activity while participants performed three near-threshold visual detection tasks with different attentional involvement: a no-cue task, a non-informative cue task (50% cue validity), and an informative cue task (100% cue validity). Cluster-based permutation statistics were complemented with Bayesian analyses to test the effect of pre-stimulus oscillatory amplitude and phase on visual awareness. We additionally examined whether these effects differed on trials with low and high oscillatory amplitude, as expected from the pulsed-inhibition theory. Our results show a clear effect of pre-stimulus alpha amplitude on conscious perception, but only when alpha fluctuated spontaneously and was not modulated by attention, supporting the notion that alpha-band power indexes neural excitability. In contrast, we did not find any evidence that pre-stimulus alpha phase influences the perceptual outcome, not even when differentiating between low and high amplitude trials. Furthermore, Bayesian analysis provided moderate evidence in favor of the absence of phase effects. Taken together, our results challenge the central theoretical predictions of the pulsed-inhibition framework, at least for the particular experimental conditions used here.

Prestimulus alpha phase modulates visual temporal integration

“…In addition, it should be noted that several studies report nullfindings with respect to phase effects on perception or neuronal activity (Ruzzoli et al, 2019;Michail et al, 2022;Zazio et al, 2022;Melcón et al, 2023). Here, we can only speculate about the discrepancies.…”

Effects of oscillation phase on discrimination performance in a visual tilt illusion

“…Critically, our purpose in examining phasic influences on the tilt illusion was to test the involvement of neural oscillations in perceptual discrimination. We asked this question in response to recent null results in studies of phasic influences on perception 24,26,70,71 that are difficult to explain given accounts of neural oscillations subserving canonical neural processes 6–8 . If phasic fluctuations in processing are fundamental to cortical computation, why are we not always able to observe their influence on behaviour?…”

An #EEGManyLabs study to test the role of the alpha phase on visual perception (a replication and new evidence)

“…Yet, despite almost a century of research, the role of low-frequency oscillations (5 -13 Hz) in perception remains a topic of debate with mixed evidence (Keitel et al, 2022;Melcón et al, 2023). Several methodological issues playing a part in this have been identified.…”