State time courses data shown in S1 Fig.

Why do we sometimes perceive a faint stimulus but miss it at other times? One explanation is that fluctuations in the brain’s internal state result in variability in perception. Ongoing neural oscillations in the alpha band (8–13 Hz), crucial in setting the internal state of the brain, have been shown as a key contributor to such perceptual variability. However, findings on how alpha oscillations modulate perceptual variability have been mixed. Some studies suggested alpha modulates perceptual criterion (c), shifting the threshold for interpreting sensory information; while others suggested alpha modulates sensitivity (d′), changing the precision of sensory encoding. Moreover, most studies have focused solely on overall alpha activity—whether within a region of interest or across the whole brain—and overlooked the coexistence of multiple distinct alpha networks, leaving it unclear whether different alpha networks contribute differently to perception. Here, to characterize how different alpha networks influence perceptual decision-making, we analyzed magnetoencephalography (MEG) data recorded while human participants performed a visual detection task with threshold-level stimuli. We found that while the visual alpha network modulates sensitivity, the sensorimotor alpha network modulates criterion in perceptual decision-making. These findings reconcile previous conflicting results and highlight the functional diversity of alpha networks in shaping perception.