Talk, Prof. Dr. Niko Busch (University of Münster): "The role of lateralized alpha oscillations in visual perception and attention"

The alpha rhythm (~10 Hz) is the most prominent oscillatory activity in the human EEG and has been closely linked to fluctuations in cortical excitability. In many visual attention and memory tasks, alpha activity becomes lateralized across hemispheres -- a pattern widely interpreted as reflecting the allocation of spatial attention. Recent studies suggest, however, that the effects of ongoing alpha rhythms on perception are better captured by models of perceptual decision-making.

I will review evidence showing that participants are more likely to report a stimulus during moments of low pre-stimulus alpha power, regardless of whether a stimulus is physically present. This effect is typically interpreted as a shift in decision criterion. These findings raise a fundamental question about the role of alpha rhythms in perceptual decisions: do fluctuations in cortical excitability alter the subjective appearance of sensory input, or do they merely reflect post-perceptual, strategic shifts in decision-making or reporting?

To address this, we employed a comparative contrast judgment task to study the effects of spontaneous alpha lateralization in the absence of directional cues. We found that such lateralization biases subjective contrast perception: stimuli appear more intense in the hemifield corresponding to the hemisphere with lower alpha power—and thus higher excitability. Extending this finding, we showed that spontaneous alpha lateralization prior to stimulus onset in a partial-report iconic memory task predicted enhanced iconic memory performance for stimuli presented in the hemifield associated with the more excitable hemisphere.

Together, these results indicate that endogenous fluctuations in alpha activity, and the corresponding changes in cortical excitability, systematically shape both perceptual and mnemonic processes by modulating the initial availability and temporal persistence of sensory information. Thereby, alpha activity modulates not only strategic decisions but also the phenomenological appearance of the visual world.

Programm "Forschungskolloquium Experimentelle Psychologie - Sommersemester 2025"