The influence of prestimulus 1/f-like vs. alpha-band activity on subjective awareness of auditory and visual stimuli.

Alpha rhythmic activity is often suggested to exert an inhibitory influence on information processing. However, relatively little is known about how reported alpha-related effects are influenced by a potential confounding element of the neural signal: power-law scaling. In the current study, we systematically examine the effect of accounting for 1/f activity on the relation between prestimulus alpha power and human behavior during both auditory and visual detection (N = 27, 19 female/6 male/2 nonbinary). The results suggest that, at least in the scalp-recorded EEG signal, the difference in alpha power often reported prior to visual hits vs. misses is probably best thought of as a combination of narrowband alpha and broadband shifts. That is, changes in broadband parameters (exponent and offset of 1/f-like activity) also appear to be strong predictors of the subsequent awareness of visual stimuli. Neither changes in posterior alpha power nor changes in 1/f-like activity reliably predicted detection of auditory stimuli. These results appear consistent with suggestions that broadband changes in the scalp-recorded EEG signal may account for a portion of prior results linking alpha-band dynamics to visuospatial attention and behavior, and suggest that systematic re-examination of existing data may be warranted. Significance Statement Fluctuations in alpha-band (∼8-12 Hz) activity systematically follow the allocation of attention across space and sensory modality. Increases in alpha amplitude, which often precede failures to report awareness of threshold visual stimuli, are suggested to exert inhibitory influence on information processing. However, fluctuations in alpha activity are often confounded with changes in the broadband, 1/f-like pattern of the neural signal. When both factors are considered, we find that changes in broadband activity are as effective as narrowband alpha activity as predictors of subsequent visual detection. These results are consistent with emerging understanding of the potential functional importance of broadband changes in the neural signal, and may have significant consequences for our understanding of alpha rhythmic activity.