Modulation of Individual Alpha Frequency with tACS shifts Time Perception

Abstract

Previous studies have linked brain oscillation and timing, with evidence suggesting that alpha oscillations (10Hz) may serve as a “sample rate” for the visual system. However, direct manipulation of alpha oscillations and time perception has not yet been demonstrated. Eighteen subjects performed a time generalization task with visual stimuli. Participants first learned the standard intervals (600 ms) and then were required to judge the new temporal intervals if they were equal or different compared to the standard. Additionally, we had previously recorded resting-state EEG from each subject and calculated their Individual Alpha Frequency (IAF), estimated as the peak frequency from the mean spectrum over posterior electrodes between 8 and 13 Hz. After learning the standard interval, participants performed the time generalization task while receiving occipital transcranial Alternating Current Stimulation (tACS). Crucially, for each subject, tACS was administered at their IAF or at off-peak alpha frequencies (IAF±2 Hz). Results demonstrated a linear shift in the psychometric function indicating a modification of perceived duration, such that progressively “faster” alpha stimulation led to longer perceived intervals. These results provide the first evidence that direct manipulations of alpha oscillations can shift perceived time in a manner consistent with a clock speed effect.

Common and distinct roles of frontal midline theta and occipital alpha oscillations in coding temporal intervals and spatial distances

“…This perceptual resolution account is also suggested by Samaha and Postle (2015) showing that occipital alpha frequency reflects the "refresh rate" of visual perception and occipital alpha represents the perceptual unit of temporal processing (Cecere et al, 2015). Consistent with this view, we predict that occipital alpha frequency should affect not only the encoding but also the retrieval and reproduction of temporal intervals, given that tACS-induced shifts in resting alpha frequency lead to shifts in subjective time experiences (Mioni et al, 2020), alpha-beta phase amplitude coupling correlates with time reproduction precision (Grabot et al, 2019), and that alpha frequency is central to the strengths of alpha-beta coupling. Future studies could investigate how interval reproduction performance is associated with alpha frequency modulation in healthy humans, as well as in the pre-clinical Alzheimer populations which show irregularities in parietal alpha oscillations (Montez et al, 2009).…”

Individual differences in alpha frequency are associated with the time window of multisensory integration, but not time perception

“…When measured over posterior electrodes, during an awake state, this peak is known as the occipital alpha peak. The precise frequency of this peak varies from one person to the next, normally within the range of 8Hz to 12Hz, but can be as low as 7Hz or as high as 14Hz (Mioni et al, 2020;Zhang et al, 2019).…”

Episodic timing: how spontaneous alpha clocks, retrospectively

“…We then identified and quantified individuals' α peak frequency (iAPF) 15 , which has been implicated in perceptual timing [16][17][18] . The α clock hypothesis predicts a positive and linear 5 correlation between iAPF and subjective duration 8 but we found no such evidence (Fig.…”