Top-down temporal attention influences visual perception through frequency-distinct modulations

Just as attention gates our conscious perception in space, the brain proactively prioritizes moments in time based on temporal regularities and allocates resources accordingly, resulting in performance benefits at attended moments. However, the neural mechanisms underlying temporal attention are not yet fully understood. One intriguing possibility relies on the now established link between fluctuations in visual perception and the neural state at the moment of stimulus presentation, such as the momentary phase of endogenous oscillations. Through this, temporal attention might affect visual perception if knowing the timing of an upcoming stimulus could be used to proactively align the optimal oscillatory phase to the moment of the predicted target onset. While this has been shown for periodic streams and attributed to oscillatory entrainment, it is unclear whether such mechanism is also involved in aperiodic, memory-based attention. In a series of experiments, we investigated whether temporal attention as guided through memorized time intervals operates through phase alignment in the occipital cortex. Participants conducted challenging visual discrimination tasks under delayed response protocols, to minimize involvement of anticipatory motor activity. Temporal predictions were provided through periodic streams or cue-interval memorized associations, and participants provided both objective discrimination performance and subjective perception. We found that memory-based temporal cueing increased phase alignment in the delta band (0.5-3 Hz) to an equal degree as rhythmic entrainment. However, alpha band (8-12 Hz), where the temporal window of optimal perception is much narrower, did not show clear phase modulation. Additionally, temporally guided anticipatory suppression of alpha-band amplitude was decoupled from the observed perceptual benefits of both subjective and objective perception. Taken together, these results show that low-frequency phase alignment can occur in the absence of oscillatory entrainment, and reveal that temporal attention changes interactions between alpha activity and behaviour compared to spontaneous fluctuations.